Chemistry marked groups, both acid; but those of the second group are the more permanent.
1st Group.—Bleaching and explosive compounds.
These seem to be three in number, namely, 1. Hypochlorous acid, ClO; 2. Chlorous acid, ClO₂; and, 3. Hypochloric acid, ClO₃. They are all either gaseous, or extremely volatile liquids, all of a much deeper yellow colour than chlorine; all explode on very slight causes, separating into chlorine and oxygen; and all possess bleaching properties, due probably to the easy separation of the chlorine they contain. They are only to be obtained by indirect processes, such as the action of chlorine on peroxide of mercury, that of hydrochloric acid on chlorate of potash, and that of sulphuric acid on the same salt. They are very dangerous, exploding with violence on the approach of a flame, often from a very slight rise of temperature, or even from the pressure of an inch or two of mercury. They seem to form among themselves compounds of similar properties, some of which compounds have been described as chlorochlorous and chloroperchloric acids. But their composition is still rather doubtful, from the extraordinary similarity of properties in all. Only one of them is practically important, and that one, hypochlorous acid, only in the form of a somewhat complex substance, containing one of its salts, namely, the bleaching powder, or chloride of lime, as it is inaccurately called. As the formation of this compound is connected with that of chloric acid, we shall describe both processes together.
2nd Group.—Colourless, permanent, strongly acid compounds.
These are two in number, namely, 4. Chloric acid, ClO₃; and, 5. Perchloric acid, ClO₄.
Chloric acid, ClO₃ = 75.5, is chiefly important and useful in the form of chlorate of potash, which is prepared as follows:—A current of chlorine gas is passed through water, in which slaked lime is suspended until the lime is entirely dissolved. In this first stage of the process, there is formed the bleaching liquor, or solution of bleaching powder. The powder is made by placing dry slaked lime in contact with chlorine gas till it refuses to absorb any more. The bleaching powder of commerce, thus prepared, contains a good deal of unaltered lime, which is left undissolved when it is acted on by water. The solution of bleaching powder thus made is the same as the bleaching liquor prepared by passing chlorine through a mixture of lime and water.
The change, in the formation of the bleaching compound, is as follows:—
\[ \text{Hydrate of Lime. Chlorine. Hypochlorite Chloride of Lime. Water.} \]
\[ 2 \text{CaO} \cdot \text{H}_2\text{O} + \text{Cl}_2 = (\text{CaO} \cdot \text{ClO}) + \text{CaCl} + 2 \text{H}_2\text{O} \]
The bleaching compound is thus a sort of double salt, formed of hypochlorite of lime and chloride of calcium, and contains the elements of 2 eqs. lime and 2 eqs. chlorine; hence the common name of chloride of lime.
This substance only bleaches in contact with acids. When it seems to do so alone, which it does very slowly, it is from the action of the carbonic acid of the air on it. The stronger acids at once disengage the whole 2 eqs. of chlorine, hence the very powerful bleaching action. The change is as follows, with sulphuric acid:—
\[ \text{Bleaching Powder. Sulphuric Acid. Sulphate of Lime. Chlorine.} \]
\[ (\text{CaO} \cdot \text{ClO}) + \text{CaCl} + 2 \text{SO}_4 = (\text{CaO} \cdot \text{SO}_4) + \text{Cl}_2 \]
Now, from the bleaching solution we can prepare chlorate of lime, and from that chlorate of potash. For, when the bleaching liquor is boiled, it loses its bleaching powers, and the following change takes place:—
\[ \text{Bleaching Powder. Chlorate of Lime. Chloride of Calcium.} \]
\[ 3[(\text{CaO} \cdot \text{ClO}) + \text{CaCl}] = (\text{CaO} \cdot \text{ClO}_3) + 3 \text{CaCl} \]
If now we add to the solution 1 eq. of chloride of po-
tassium, and evaporate, chlorate of potash crystallizes, and only chloride of calcium remains dissolved.
In practice, the chloride of potassium is added to the bleaching solution before boiling it, when the object is to obtain chlorate of potash. This salt, being sparingly soluble in cold water, crystallizes readily when the solution is boiled down to a certain point, leaving in solution the very soluble chloride of calcium.
From chlorate of potash, chloric acid may be obtained by distillation with sulphuric acid, but when concentrated, a part is decomposed by the heat. The addition of a little water prevents this, and we obtain a solution of chloric acid nearly pure. When free from water, it forms crystals. Its solution is colourless and strongly acid, oxidizing organic matter, and forming with ammonia a dangerously explosive salt. It is only used in the form of chlorate of potash prepared as above. This salt, when heated, gives off all its oxygen quietly, as explained under oxygen. But when mixed with combustible matter, such as sulphur, phosphorus, charcoal, or sugar, the mixture deflagrates or explodes by the contact of a spark, by friction and percussion, and in the case of charcoal even spontaneously, so that it is too dangerous to be employed for gunpowder. But when duly mixed with sulphur or phosphorus, gum and water, with the addition of a little charcoal, the mixture is extensively used for lucifer matches, exploding and setting fire to the sulphur on the match, by friction on any hard body. A mixture of chlorate of potash with sugar takes fire on being touched with sulphuric acid, which, acting on the chlorate, produces hypochloric acid, and this at once sets fire to the sugar.
Perchloric acid, ClO₄ = 91.5, is easily obtained, in combination with potash, by heating the chlorate of potash till 3d only of its oxygen is expelled, which is known by the melted salt becoming quite thick and pasty, and requiring a stronger heat to expel the remaining 3ds of the oxygen. The cooled mass consists of perchlorate of potash and chloride of potassium; thus—
\[ \text{Chlorate of Potash. Perchlorate of Potash. Chloride of Potassium. Oxygen.} \]
\[ 2(\text{KClO}_4) = (\text{KClO}_3) + \text{KCl} + \text{O}_2 \]
It is dissolved in the smallest possible quantity of boiling water, and on cooling the very sparingly soluble perchlorate of potash crystallizes. This salt, distilled with sulphuric acid and a little water, yields a solution of perchloric acid; the acid when dry forms crystals. Perchloric acid is colourless and strongly acid. It produces in all solutions of potash a very sparingly soluble precipitate of perchlorate of potash, quite insoluble in weak alcohol. Hence the acid is used to distinguish and to separate potash from soda, the perchlorate of soda being very soluble even in alcohol.
Perchlorate of potash explodes feebly with combustible matter on heat being applied. It is not easy to see how an acid containing 7 eqs. of oxygen should be less disposed to yield oxygen to combustible matter than one with 5 eqs. only. But there is evidently something in the constitution of the molecule which renders it more permanent than that of chloric acid, which itself is far more permanent than those of hypochloric, chlorous, and hypochlorous acids.
Chlorine and Nitrogen.
When chlorine gas is placed in contact with a warm solution of chloride of ammonium (sal-ammoniac), it is absorbed, and oily drops are formed, which sink through the liquid. These are frightfully explosive, especially on simple contact with greasy, oily, or combustible substances. This explosive compound has been described as a compound of nitrogen with chlorine, NCl₅, or, according to some, NCl₆. But very recent researches have shown that this is not the case, and Chemistry. Bromine.
Symbol Br. Equivalent = 80.
Bromine stands unquestionably next to chlorine, and is so very analogous to it, that a very brief notice will suffice. It is found united to sodium, potassium, or magnesium, in very small proportion, in sea-water, and in saline springs. Those of Kreuznach are comparatively rich in bromides, as is also the water of the Dead Sea, which is simply a concentrated sea-water.
It is obtained from the mother liquor or bittern which remains after salt-water has been evaporated to yield crystals of salt, and refuses to yield any more. This liquid contains much of the chlorides of potassium, calcium, magnesium, and a small proportion of some bromide or bromides. If we pass through it a current of chlorine, or, what is the same thing, add to it a little sulphuric acid and peroxide of manganese, which, with the chlorides, produce free chlorine; the chlorine displaces the bromine, which, being set free, colours the liquid of a strong orange-yellow. Heat is applied, and the vapour of water, distilling over, carries with it the vapour of bromine, which collects in the receiver, partly as heavy drops of a deep red colour, which are pure bromine, partly as an aqueous solution of bromine of an orange colour, which floats above. Excess of chlorine must be avoided, as it combines with the bromine, forming a chloride of bromine. If the aqueous solution be shaken with a little ether, the ether dissolves the bromine and rises to the surface, of a deep red colour. This is added to the nearly pure bromine collected below, and the whole is then mixed with as much solution of caustic potash as entirely destroys the colour, by which the bromine is converted into two salts, bromate of potash and bromide of potassium. (Chlorine with potash undergoes a similar change, and chlorate of potash was formerly thus prepared.) The change is represented as follows:
\[ \text{Br}_2 + 6 \text{KO} = \text{KO}_3\text{Br}_2 + 5 \text{KBr} \]
The solution is dried up and ignited, which expels the oxygen of the bromate, converting it also into bromide; so that we have \((\text{KO}_3\text{Br}_2) + 5 \text{KBr} = 6 \text{KBr} + \text{O}_2\). Lastly, the bromide of potassium is heated with sulphuric acid, a little water, and peroxide of manganese, when pure bromine passes over, with some water. The greater part of the bromine collects below an aqueous solution of a small part of it, and may be withdrawn by a pipette.
Bromine is a heavy dark red volatile liquid, of a most pungent odour, strongly affecting the mucous membrane of the nose and eyes, and producing a profuse catarrhal discharge. Its vapour must be carefully avoided. It is named, indeed, from its strong smell. Its vapour or gas is of the same red colour as that of nitrous acid, and very dense, its specific gravity being about 5500, rather more than twice as heavy as chlorine gas. Bromine is very poisonous; a drop placed on the beak of a small bird soon proving fatal. It has feeble bleaching properties compared to chlorine.
Bromine is in all its relations so perfectly analogous to chlorine, that it is unnecessary to go into detail. What is true of chlorine is true of bromine, with regard to the other elements, in all cases where bromine combines with them. The chief difference is, that its equivalent is higher, and its affinities weaker, than those of chlorine, which displaces it from all its compounds.
With hydrogen it forms hydrobromic acid, \(HBr\); equivalent = 81; perfectly analogous to hydrochloric acid, but much more dense. It is absorbed by water with even greater energy.
With oxygen it forms bromic and perbromic acids, analogous in composition and properties to chloric and perchloric acids. Bleaching oxides or acids of bromine are not yet known.
To bromine and nitrogen the same remarks apply as to chlorine and nitrogen. The compounds of bromine with metals are so like those of chlorine, that they are hardly distinguishable from them.
Bromine will probably be found useful in medicine. At present its chief use is, with chlorine and iodine, in photography. It contributes to the formation of the most sensitive surfaces.
Iodine.
Symbol I. Equivalent = 127.
This element is the third of the remarkable group, of which the two other members have just been described. It is found in the ashes of marine plants, which form kelp, varce, and barilla. It is, no doubt, derived by the plants from the sea-water; but its proportion in that water is so small as hardly to admit of being detected directly. It is also found in the ashes of many land plants, especially such as grow near the sea; in some salt springs in small proportion, and in a few rare minerals.
It is obtained from kelp, after all the crystallizable salts have been separated by evaporation. The residual or mother liquid contains the iodide of sodium, potassium, or magnesium, mixed with chlorides, sulphurates, and sulphites, as well as various other impurities. It is extracted by adding first an excess of sulphuric acid, which disengages a vast amount of gases, hydrosulphuric and sulphurous acids, and causes a copious deposition of sulphur. On cooling, sulphates of soda, potash, and magnesia, are deposited, and the liquid, poured off from these, is heated with peroxide of manganese as long as purple vapours of iodine come off. In another method the iodine is precipitated as subiodide of copper, \(CuI\), which is afterwards decomposed by sulphuric acid and peroxide of manganese. The vapours of iodine condense into crystals in the receiver, along with some water.
Iodine is a black solid, crystalline, very brittle, of a quasi-metallic lustre, and volatile. When dry it is converted into vapour, without melting, at 320° nearly; but if water be present the iodine passes rapidly over at 212°. Its vapour is of a fine purple or violet colour, hence the name, and is very heavy, being nearly 9 times denser than air. Heated under pressure, iodine melts to a brown liquid. It is almost insoluble in water, 1 part requiring 7000 of cold water to dissolve it; but even this colours the water brown. It is very soluble in alcohol, ether, and similar liquids. Iodine hardly possesses bleaching properties. It stains organic matter deep yellow, and corrodes it (for example, paper) rapidly. Its distinguishing character is that of striking, with a cold infusion of starch or with starch paste, a deep blue. The blue substance seems not to be a definite compound, but to consist of starch, with minute particles of iodine mechanically diffused through and adhering to it. The violet-blue colour seems to be that of finely-divided iodine, as is seen in its vapour. Heat destroys the colour of the iodide. Chemistry of starch. This character distinguishes iodine from bromine, which colours starch brown.
Iodine is entirely analogous to chlorine and bromine; the three bodies forming a group in which bromine stands in every point, in form, density of vapour, strength of affinity, and atomic weight, precisely between chlorine and iodine. As bromine is perfectly analogous to chlorine in its compounds, so iodine is analogous to bromine.
With hydrogen it forms hydriodic acid, HI, which is so similar to hydrochloric and hydrobromic acids, that it cannot be distinguished from them, except by proving that it contains iodine. It is a colourless acid gas absorbed to a prodigious extent by water, forming grey fumes in moist air, and white fumes with ammonia. To obtain it, iodine is first placed in contact with phosphorus, in a tube filled with carbonic acid gas, to exclude oxygen. The two bodies combine with a flash of light, forming, according to the preparations used, either the teriodide of phosphorus, PI₃, or the periodide, PI. When cold, water is added, a conducting-tube adapted, and heat applied. The action is as follows, taking the periodide; but it is the same, mutatis mutandis, for the other:
Periodide of Water. Phosphoric Acid. Hydriodic Acid. PI₃ + 5 HO = PO₅ + 5 HI
The action of hydriodic acid on metals and on metallic oxides is exactly analogous to hydrochloric or hydrobromic acid. An iodide of the metal is formed; and in the one case hydrogen is liberated, in the other water is produced. The iodides of some metals have fine colours. Iodide of lead is bright yellow; periodide of mercury is of a bright scarlet.
With oxygen iodine is not known to form any bleaching compounds, but it forms iodic acid, IO₃, and periodic acid, IO₄, corresponding to chloric and perchloric acids. Iodate of potash is formed, along with iodide of potassium, when iodine is acted on by caustic potash, precisely as in the case of bromine and chlorine, I₂ + 6 KO = KIO₃ + 5 KI.
The mixed salts being dried, alcohol dissolves the iodide, leaving the iodate, from which iodic acid may be obtained if required. Iodine may also be oxidized into iodic acid by boiling with the strongest nitric acid. Iodic acid is a crystalline solid, very soluble and very acid. Periodic acid is formed by a circuitous, indirect process. It is not applied to any use.
The compound, an explosive black powder, hitherto called iodide of nitrogen, appears from recent researches to have a different composition.
Iodine combines both with chlorine and bromine. With chlorine it forms several compounds, one of which is so like bromine, that when bromine was accidentally obtained by Liebig from the water of Kreuznach, which contains both chlorine and iodine, he took it for chloride of iodine, and thus missed the discovery of bromine, which was soon after made by Balard. The supposed chloride was then found to be pure bromine.
The compounds of chlorine both with bromine and iodine, as well as those of bromine and iodine, have nearly intermediate characters, and are not very precisely known. They are all more or less used in photography.
The iodides of metals, as well as the bromides, are entirely analogous to the chlorides, but are, those of iodine more particularly, less soluble in water.
Iodine is much used in medicine, both as iodine in tincture and ointment, and in the form of iodides, such as those of potassium, iron, zinc, lead, and mercury.
The extraordinary analogy between the three elements just considered seems to indicate something common to all three. But if they contain a common element, they must be really compounds, for their differences must depend on something peculiar to each. It is worthy of notice that the relation between them as to physical properties, affinity, and Chemistry, atomic weight, is precisely that between three contiguous members of what is called in organic chemistry a series of homologous compounds. Thus methyl alcohol, ethyl alcohol, and propyl alcohol, form a precisely parallel group. Now, the first of these is converted into the second by the addition of C₆H₁₂ and the second into the third in the same way:
Methylic alcohol, .............. C₆H₁₂O + C₆H₁₂ Ethyl alcohol, .................. C₆H₁₂O + C₆H₁₂ Propyl alcohol, .................. C₆H₁₂O &c. &c.
It is therefore quite conceivable that there may be a similar relation between chlorine and bromine, bromine and iodine. But as to what is here the common difference, corresponding to C₆H₁₂ in the other case, we can say nothing. We can only point out the probability that such a relation exists, and leave the question to be decided by research, when our means of research shall have been improved; for hitherto all our efforts to convert chlorine into bromine, or bromine into iodine, and vice versa, have failed.
7. Fluorine.
Symbol F. Equivalent = 18-9.
This element is not yet known in a separate form; but from the character of all its compounds, it is obviously very analogous to the three preceding elements. The reason why we have not yet obtained it uncombined is, that its affinities are so powerful, that it corrodes all vessels in which the attempt has been made. It has been suggested that it might be isolated in vessels of fluor-spar; but no distinct results have yet been obtained. According to some it is a yellow gas like chlorine; but there is reason to think that chlorine was at all events mixed with the supposed fluorine.
Fluorine is found in nature combined with calcium as fluorspar or Derbyshire spar, and occurs also in small proportions in mica, topaz, cryolite, and a few other minerals. Fluoride of calcium, or fluor-spar, is also an essential ingredient, in small proportion, of bones, and is to be detected almost everywhere, in rocks, soils, springs, the sea, the ashes of plants, and the animal fluids, but in very minute quantity.
With hydrogen, fluorine forms its most important compound, hydrofluoric acid (often called fluoric acid), HF = 19-9. This acid is obtained by distilling fluor-spar with sulphuric acid in vessels of lead, silver, gold, or platinum, for it corrodes glass and porcelain. The change is as follows:
Fluoride of Calcium. Sulphuric Acid. Salpate of Lime. Hydrofluoric Acid. CaF₂ + H₂SO₄ = CaSO₄ + HF
It forms a very volatile, fuming, and frightfully corrosive liquid, which produces intense heat when mixed with water; and a drop of which falling on the skin produces, even when instantly washed away, a very painful sore, which is extremely difficult to heal. The hands should be protected even against the vapour, for it penetrates under the nails, producing there sores which, from their confined position, cause intolerable pain.
It is in its relations very analogous to hydrochloric acid, &c., acting on metals and metallic oxides in the same way, and forming fluorides very similar to the chlorides. Its distinguishing character is its power of corroding glass and all silicious compounds, in virtue of the strong affinity of fluorine for silicon, with which it forms a gaseous compound. This property is not only applied to etching on glass, but to the detection of minute traces of fluorine or fluorides. The substance suspected to contain it, whether an ash, a mineral, the residue of any water, or the deposit from sea-water when boiled, is placed in a platinum vessel with pure sulphuric acid. A plate of glass is covered with melted wax, and when cold, marks are traced in the wax with a sharp point, which exposes the glass under these Chemistry marks. The plate is then laid over the vessel with the materials, to which a very gentle heat is applied. The vapour of hydrofluoric acid, if a fluoride be present, rises and acts on the exposed lines. After a certain time, longer in proportion as the amount of fluorine is smaller, the wax is removed, and the lines are found indelibly etched on the glass.
The only use to which hydrofluoric acid is applied is that of etching on glass, and dissolving siliceous minerals for analysis, by which means the whole silica is dissipated as gas, and the other elements remain. The presence of fluoride of calcium in bones is probably connected with their hardness and toughness. It is conjectured that the presence of the fluoride prevents the phosphate of lime from crystallizing, as it has a strong tendency to do, and thereby becoming brittle. Fossil bones and coprolites, rich in bone earth, invariably contain a small amount of fluoride of calcium. It has been said that the proportion is greater in fossil than in recent bones; but it seems rather that, from the absence of animal matter, it is more readily detected in the former.
No compounds are yet known of fluorine with oxygen, nitrogen, chlorine, bromine, or iodine. Its affinities are so very powerful for the positive elements, that it is probable it may prove to be more highly negative than oxygen, which would account for its exhibiting little or no attraction for that element.
(b.) POSITIVE OR COMBUSTIBLE METALLOIDS.
8. Carbon.
Symbol C. Equivalent = 6.
This most important element occurs in nature in several forms, more or less pure. Crystallized, it is found in two allotropic forms; one transparent, hard, and colourless, is the diamond, the other black and soft, is plumbago or black lead, or graphite, the crystalline form of which is quite different. A third, amorphous form, is found in anthracite or blind coal. It occurs also, combined with oxygen, as carbonic acid gas, in the atmosphere, in waters, in the chokedamp of mines, in volcanic districts; and the same acid, combined with lime, forms marble, limestone, chalk, shells, calcareous deposits, and calcareous or Iceland spar. Other carbonates occur in the mineral kingdom, such as those of magnesia, iron, lead, copper, &c. Carbon is the chief ingredient of all animal and vegetable substances; also of coal, which is vegetable matter in an altered state, and of peat, lignite, brown-coal, wood-coal, jet, asphalt, bitumen, &c., all of which have a similar origin.
Pure carbon, in the form of diamond, which forms octahedral crystals, is distinguished by its extreme hardness and by its action on light, giving it the fine play of colours for which it is valued. Graphite occurs in micaceous scales, which are short prismatic crystals. It is black and opaque, with somewhat of a metallic lustre. Anthracite has no regular form, and is dull, black, and opaque. So also are wood, charcoal, and lamp-black; the latter being pure carbon from oils or resins, the former, like anthracite, containing, as ashes, the mineral elements of the plants which yielded them. In all its forms it is a bad conductor of heat, but when dense and compact it conducts electricity. It is totally infusible by any heat we can produce. When heated to redness in air or oxygen, it burns without flame, frequently with sparks, forming carbonic acid gas. Diamond can easily be burned in oxygen, or even in air, by the heat of a glass-house furnace. No liquid is yet known which can dissolve carbon as such.
Carbon has the power of attracting, in a manner somewhat obscure, both gaseous and dissolved matters, and collecting them in its pores. Thus it absorbs large quantities of most gases; and when introduced into a liquid, generally removes from it any organic colouring matter that may be present, and very frequently saline substances also. It absorbs and renders innocuous all offensive effluvia. Animal Chemistry, charcoal has the greatest power in this way, either because it is more porous, or because it contains nitrogen, and is not in fact pure carbon.
Carbon and Oxygen.
1. Carbonic Oxide, CO = 14.
This is a gas formed when carbon burns with an insufficient supply of oxygen, or when carbonic acid gas, CO₂, is passed over red-hot charcoal. It may be formed also by heating with excess of sulphuric acid, oxalic acid and its salts, formic acid and its salts, or ferrocyanide of potassium. When oxalic acid is employed, it is resolved into equal volumes of carbonic acid and carbonic oxide, while water combines with the sulphuric acid; thus—
\[ \text{Oxalic Acid} + \text{Sulphuric Acid} = \text{Diluted Carbonic Acid} \]
Formic acid consists of \(C_2H_4O_3\) or \(C_2H_2O_4\); and yields precisely in the same way water and pure carbonic oxide gas. \(C_2H_4O_3 = 2HO + 2CO\). The ferrocyanide of potassium first yields hydrocyanic acid, which, by the action of mere sulphuric acid reacts on water, producing formic acid and ammonia, and the formic acid is decomposed as above. When mixed with carbonic acid, the gas is purified by means of lime or potash, which absorb the carbonic acid, leaving the carbonic oxide. It is collected over water.
It is a colourless gas of specific gravity 9721, without taste or smell, which, when heated in air, takes fire and burns with a pure blue lambent flame, being oxidized into carbonic acid. In every large coal fire, the air entering below forms carbonic acid, which, passing through the deep mass of red-hot charcoal, is converted into carbonic oxide, thus, \(CO + C = 2CO\). The carbonic oxide rising to the surface, there burns with its peculiar blue flame, as may be seen in every large fire after it has burned so far that no more gas issues from the coal, and the whole is in a red glow. The blue flame is supposed to indicate frost, but it is evident that it indicates simply a large red-hot fire, which, of course, is more frequent in frosty weather than in summer.
This gas occurs in mines, along with carbonic acid and carburetted hydrogen. It is poisonous when inhaled.
Carbonic oxide, or a substance polymeric with it, seems to exist in some organic compounds as a radical. It is not applied to any use, although it has a share in the reduction of metal, such as iron, being formed in large quantity in the deep smelting furnaces, and having, from its tendency to take up an additional eq. of oxygen, a considerable deoxidizing power.
2. Carbonic Acid, CO₂ = 22.
This is a much more important compound. It is a gas which occurs abundantly in nature, as has been stated under carbon, both free and combined with lime and other bases. It is also abundantly formed in various natural and artificial processes, in the respiration of animals, in the decay of dead organic matters, in fermentation, and in combustion. It is from these sources principally that the carbonic acid of the atmosphere, so essential to vegetation, is supplied; and it is consumed by plants as fast as it can be produced, since its amount never exceeds, in free air, about \(\frac{1}{100}\)th of the bulk or volume of the air.
To obtain it pure, carbonate of lime, that is, marble limestone or chalk, is acted on by diluted hydrochloric acid. The action is very simple. \(CaO, CO_2 + HCl = CaCl + HO + CO_2\). Chloride of calcium and water are left, while carbonic acid gas passes off and is collected over water, which absorbs a certain amount of it, but not so much as to It is colourless and transparent, has a sharp acidulous taste, and a certain pungency of smell, or rather a peculiar action on the organs of respiration, and not a true odour. It extinguishes all burning bodies, and is equally fatal to animal life, being poisonous even when diluted with air, and not merely negatively injurious like nitrogen. It is distinguished from all other gases by its rendering lime-water milky from the formation of the insoluble carbonate of lime.
It is a heavy gas, its specific gravity being 1527.7. We do not know the volume of the carbon in it in the state of gas, but we know that it contains its own volume of oxygen, and that the whole weight of the carbon is added to that of the oxygen in the same volume. So that we have—
One volume oxygen, specific gravity ................. 1111.1 Carbon, volume uncertain, weighing .................. 416.6
One volume carbonic acid, specific gravity .......... 1527.7
If the carbon united to 1 volume of oxygen be, as gas, equal in volume to the oxygen, then 1 volume of gaseous carbon must weigh 416.6, when 1 of oxygen weighs 1111.1; and its specific gravity would be 416.6. But this would imply that the 2 volumes of the elements were condensed into 1 volume of the compound, of which we have no example. If, on the other hand, carbonic acid be formed of 2 volumes of oxygen and 1 volume of gaseous carbon, the 3 volumes condensed into 2, which is a very common occurrence, as in water, protoside of nitrogen, &c., then the 416.6 will represent the weight only of half a volume of carbon, and the weight of an entire volume, or the specific gravity, will be $416.6 \times 2$, or 833.2. This latter view of the specific gravity of gaseous carbon, which cannot be directly determined, is considered the most probable. On the same supposition carbonic oxide will be formed of 1 volume of gaseous carbon and 1 volume of oxygen, united without condensation, or so as to form 2 volumes of the compound, which is also a very common occurrence, as in hydrochloric acid, &c. We have mentioned this here, to explain how chemists calculate the probable density in the gaseous form of a substance, such as carbon, which is not known in that form, except in compounds.
From its weight, carbonic acid gas may be poured out of one vessel into another, like water; and if a lighted candle be first placed in the lower vessel, it will be quickly extinguished, as the invisible gas flows down to it. The gas may even be poured in the open air so as to fall in a narrow stream on the candle and extinguish it. For the same reason this poisonous gas is apt to accumulate in deep pits, wells, or mines, where it is very dangerous. A candle let down first will indicate, according as it burns brightly or dimly, or is extinguished, the purity or impurity of the air in such places, before any one descends; and this precaution should never be neglected. The gas often accumulates in the huge vats of the brewers, and has frequently caused fatal accidents there as well as in mines or pits. It is the choke-damp of miners.
Carbonic acid is liquefied by a pressure of 36 to 40 atmospheres, according as the temperature varies from 32° to about 60°. The condensed acid is very dangerous, having often, by its enormous pressure, burst very strong vessels and caused fatal results. It is best condensed by being forced by means of a very powerful forcing pump into a strong copper vessel, which, if it should at any time give way, tears instead of bursting. When allowed to escape through a small aperture, it assumes the gaseous form with almost explosive force, but is manageable, and if the current be made to circulate through a brass box, the evaporation of part produces a cold so intense as to solidify the rest. The solid acid is exactly like snow, and evaporates much more slowly than the liquid. But if mixed with ether, the mixture evaporates so rapidly, that by its means several pounds of mercury may be frozen hard in a minute or two. The liquid acid expands by heat to a remarkable degree.
Carbonic acid gas is absorbed by water to a small extent under the ordinary pressure, but under an increased pressure the quantity absorbed increases in proportion to the pressure; the water always absorbing about its own volume, whatever the pressure, but the gas being of course more and more condensed as the pressure increases. The solution sparkles, and has a pleasant acidulous taste, as observed in many mineral waters. The addition of a little carbonate of soda (or potash) causes water to absorb much more, and when this is combined with high pressure, a very large quantity is taken up, which escapes on the pressure being removed. This is the nature of soda water. Champagne is wine bottled before the fermentation is complete, and therefore charged with carbonic acid under pressure of the gas itself, which escapes with violence when the cork is drawn. All effervescing wines or other beverages are in the same way more or less charged with carbonic acid.
The solution of carbonic acid in pure water, or in water containing a little potash or soda, under the ordinary or a slightly increased pressure, occurs as a mineral water in many springs, especially in volcanic districts, even in such as, like Auvergne and the Eifel, have not been the scene of active volcanic action since the appearance of man on the earth. In the Eifel the soil is everywhere impregnated with the gas, which of course appears in all the springs. The Grotta del Cane, near Vesuvius, is a cave containing a small lake or pool, through which carbonic acid constantly bubbles, and from its weight remains near the floor of the cave, so that a dog, whose head is near the ground, falls down insensible, while men, whose heads are in pure air, perceive no effect. The animal recovers, if at once removed into pure air and thrown into the lake outside. This mode of applying the cold affusion is effectual in causing instinctive inhalations of pure air, and indicates the dashing of cold water on the face and chest of those poisoned by the gas as one of the most efficient remedies.
The solution of the gas in water reddens vegetable blues like other acids; but on standing, or after boiling, the blue colour returns, the acid being dissipated. This serves to distinguish carbonic acid from most other acids.
The same solution added to lime water renders it milky, by forming insoluble carbonate of lime, CaO, CO₂. But the addition of more carbonic acid clears all up again, forming the soluble bicarbonate, CaO, 2 CO₂. Such a solution containing carbonate or bicarbonate of lime, dissolved in excess of carbonic acid, is exceedingly common in all districts where limestone occurs. The amount of lime present varies very much, but even a few grains per gallon render the water very hard. Such, indeed, is the usual cause of hardness in water, although the presence of sulphate of lime or gypsum also contributes to it in many cases. The rain dissolves carbonic acid as it passes through the air, and more in filtering through the soil, and when it now meets with chalk or limestone it dissolves it and becomes hard. Some waters contain 10 grains of carbonate of lime in the gallon, others a good deal more; very hard waters frequently 70 or 80 grains, and in some cases so much as 150 grains. Chemistry, and upwards. Such waters are useless for the purposes of washing; and generally for culinary purposes, and above all unfit for steam-boilers; for they deposit, on being boiled, a crust of carbonate of lime which is most injurious, and is often the cause of explosions. It is singular that hard waters—not, however, the hardest, but such as that of the Thames, and some still harder near Edinburgh, where from the abundance of the carboniferous limestones they are very common—are the best for the purposes of the brewer of ale or porter. On the small scale the carbonate of lime in hard water of this kind may be separated by boiling, but this is impracticable on the large scale. Professor Clark's process consists in adding to the water as much lime, dissolved in water (lime water), as it already contains in the form of bicarbonate, and more if there be an excess of carbonic acid beyond this. The added lime converts the soluble bicarbonate into the insoluble neutral carbonate, which is thus explained, $\text{CaO} + \text{CO}_2 = \text{CaCO}_3$.
The chief use of carbonic acid is to form the principal part of the food of plants, which derive from it, and therefore from the atmosphere, the whole of the immense quantity of carbon they contain. The carbon of the animal world being derived directly or indirectly from plants, for carnivorous animals feed on such as feed on plants, is also derived from the same source; and the carbon of dead animals and vegetables again takes, in the process of decay, the form of carbonic acid, in which it becomes the food of a new generation of plants and animals. The other uses of carbonic acid, as a remedy and in various beverages, are familiar, and have been already mentioned. The salts of this acid are characterized by effervescing with strong acids.
Some other compounds are frequently described as compounds of carbon and oxygen, such as oxalic acid, melitic acid, &c. But in fact they all contain hydrogen also, and belong to organic chemistry.
Carbon and Hydrogen.
The compounds of these two elements are extremely numerous, far more so than those of any two elements whatever. Indeed there seems hardly any limit to their number. They are all of organic origin, and belong to organic chemistry, under which we shall describe them more particularly. Here we shall only say, that, being formed of two combustibles, they are all eminently combustible, and are used as combustibles. They occur in all forms, solid, liquid, and gaseous; and of all different proportions of the two elements. They form various series, some of which are homologous, others polymeric. In one homologous series, that of olefiant gas, the proportion is that of 1 eq. of each, but the absolute amount varies from C$_4$H$_8$, and C$_5$H$_{10}$, which are gaseous, to C$_6$H$_{14}$, and C$_7$H$_{16}$, which are liquid, and to C$_8$H$_{16}$, and C$_9$H$_{18}$, which, with many others, are solid. In another exactly parallel series, that of marsh gas, the proportion is such that there are always 2 eqs. of hydrogen more than of carbon. It begins with C$_2$H$_4$, C$_3$H$_6$, and so on to C$_{10}$H$_{22}$, C$_{11}$H$_{24}$, C$_{12}$H$_{26}$, &c.; those low in the scale being gaseous, those higher liquid, and higher still solid. We find similar characters in the series of methyl and ethyl, in which the hydrogen always exceeds the carbon by 1 eq.; thus we have methyl C$_2$H$_5$, ethyl C$_3$H$_7$, amyle C$_4$H$_9$, cetyl C$_5$H$_{11}$, melissyle C$_6$H$_{13}$, &c. As an example of another kind of series of carb-hydrogens, we may mention certain essential or volatile oils, such as oil of lemons C$_9$H$_{16}$, oil of turpentine C$_9$H$_{16}$, another oil C$_9$H$_{16}$, &c. All these matters belong to organic chemistry, and therefore we only indicate them very briefly, that the reader may see how very peculiar is the relation of carbon to hydrogen, which is evidently connected with the fitness of these elements to constitute organic, that is, animal and vegetable compounds. Coal gas, naphtha, paraffine, and many volatile oils, belong to this group of compounds, which therefore admits of many useful applications. The fire-damp or explosive gas of mines is a mixture of some gaseous carbo-hydrogens with air.
Carbon and Nitrogen.
These elements, under certain circumstances, combine to form a very remarkable and important compound, namely, Cyanogen, C$_2$N or Cy, which is a compound acid radical or salt radical, entirely analogous to chlorine in its chemical relations.
Cyanogen, C$_2$N = Cy = 26, is found, as hydrocyanic acid, in oil of bitter almonds; but as that is a product of fermentation, and is not present in the dry seeds, it is doubtful whether hydrocyanic acid exist ready formed in plants. But there must be some compound of cyanogen, which, when water is added to the bitter almonds, or to the kernels of stone fruit, produces hydrocyanic acid. As urea is formed from cyanic acid and ammonia, it is probable that the animal body also contains some compound of cyanogen.
It is formed artificially when organic matter containing nitrogen is exposed to heat in close vessels. But being gaseous, it is dissipated and lost, unless some means be taken to prevent this. If potash or carbonate of potash be added, cyanide of potassium is formed, and this salt is permanent at a red heat. When water is added, however, to the heated mass, consisting chiefly of animal charcoal and cyanide of potassium, that salt is decomposed, as follows:
$$\text{K}_2\text{Cy} + \text{HO} = \text{K}_2\text{CO}_3 + \text{NH}_3 + \text{H}_2\text{O};$$
that is, bicarbonate of potash is left, and ammonia and hydrogen are given off. To obtain cyanogen in a permanent form, there must be added, either before or with the water, iron, oxide of iron, or sulphuret of iron, all of which are dissolved by cyanide of potassium. Suppose iron to be used, then $3(\text{K Cy}) + \text{Fe} + \text{HO} = (2\text{K Cy} + \text{Fe Cy}) + \text{K}_2\text{O} + \text{H}_2$. With oxide of iron no hydrogen is given off; and with sulphuret of iron sulphuret of potassium, K$_2$S, is formed, instead of KO; but in all these cases the compound $2\text{K Cy} + \text{Fe Cy} = \text{Cy}_2\text{K}_2\text{Fe}$, which is ferrocyanide of potassium, is formed. On evaporation this salt forms large and fine yellow crystals, which are very permanent, and are manufactured on the large scale, and of great purity, being much used in dyeing and calico-printing.
This salt may be viewed either as a double salt, composed of 2 eqs. KCy with 1 eq. FeCy, or, as is now generally admitted, as formed of the compound radical ferrocyanogen Cy$_2$Fe = CyF, which, being dibasic, takes up 2 eqs. of potassium, forming the yellow salt, Cy$_2$K$_2$. The crystals contain in addition 3 eqs. water, and are Cy$_2$K$_2$3 HO.
From this salt all the compounds of cyanogen and cyanogen itself are prepared. To yield cyanogen, it is heated with bichloride of mercury, which acts on the 2 eqs. KCy, that are present by their elements; $2\text{K Cy} + \text{Hg Cl}_2 = 2\text{K Cl} + \text{Hg Cy}_2$. This forms bicyanide of mercury, but the heat employed decomposes this salt into cyanogen and mercury.
Cyanogen is a colourless gas, collected over mercury, of a very pungent smell, inflammable and burning with a pink flame. Water absorbs it, and the solution, if kept, undergoes a spontaneous change, by which numerous compounds are formed, a kind of putrefaction. Cyanogen and water contain the four elements, carbon, hydrogen, nitrogen, and oxygen, and there are formed compounds of these, and compounds of these compounds again, so as to give rise to very complex changes. Carbonic acid, ammonia, hydrocyanic acid, cyanic acid, cyanate of ammonia, urea, formic acid, and dark brown insoluble compounds containing cyanogen, but not fully studied, are formed.
Cyanogen is very analogous to chlorine in its relations. It forms with hydrogen hydrocyanic acid, H Cy, and with Chemistry: metals cyanides, corresponding to the chlorides, as K Cy and Hg Cy, corresponding to K Cl and Hg Cl. With oxygen it forms three polymeric acids, cyanic, fulminic and cyanuric acids. But it is chiefly remarkable for forming with sulphur, and also with many metals, compound radicals, such as sulphonycyanogen CyS = CsCy, ferrocyanogen CyFe = FeCy and others, all of which, like cyanogen itself, form acids with hydrogen, and salts with metals.
Hydrocyanic acid, H Cy = 27, is obtained by heating ferrocyanide of potassium with sulphuric acid and water. Ferrocyanide of potassium contains CyKFe, and when the acid acts on it, there are first formed cyanide of potassium and cyanide of iron, the latter separating as an insoluble powder, 2 K Cy + FeCy. The FeCy remain unchanged; but the 2 K Cy act on sulphuric acid, thus, 2 K Cy + 2 H SO₄ = 2 (K,SO₄) + 2 H Cy. The acid, H Cy, being volatile, distils over with water. It is obtained pure by adding chloride of calcium, which forms a heavy oily solution with the water, above which floats the pure dry acid, and may be drawn off by a pipette. It is very volatile, lighter than water, has a peculiar oppressive smell, and is very poisonous, even when smelled at, in its pure state. Before smelling it, it should be diluted. It is the well known poison prussic acid.
It is used in a diluted form in medicine, and the medicinal acid ought to contain in 100 parts not more than 3 of the pure acid. Its strength is ascertained by converting a measured portion into cyanide of silver, which is insoluble, and is formed on the addition of nitrate of silver, H Cy + AgNO₃ = HO, NO₃ + AgCy. As the cyanide of silver, AgCy, weighs very nearly five times as much as the hydrocyanic acid, H Cy, for H Cy = 27 and AgCy = 134, we can easily ascertain the weight of the pure acid by dividing that of the cyanide of silver by 5.
The presence of hydrocyanic acid is detected by converting it into Prussian blue, which is done by adding, first potash, then mixed sulphate of protoxide and sesquioxide of iron, leaving an excess of potash, and after a few minutes adding lastly hydrochloric acid, which dissolves all but the Prussian blue. If the quantity of hydrocyanic acid be very small, the liquid, after adding the hydrochloric acid, must be allowed to stand for 24 hours, when the blue will appear at the bottom of the vessel.
Or the hydrocyanic acid may be converted into sulphocyanide of iron, which is of a deep blood-red colour. To do this, add to the diluted acid a little sulphuret of ammonium with a little sulphur, and evaporate to dryness in a water bath. To the dry mass which now contains sulphocyanide of ammonium, add a salt of sesquioxide of iron, and the red colour will appear.
The three compounds of cyanogen and oxygen are CyO, HO, cyanic acid; CyO₂, 2 HO, fulminic acid, and CyO₃, 3 HO, cyanuric acid. The first and the last are both obtained from urea, and their relation to that compound and to each other is fully detailed under the head of polymerism and isomerism in organic compounds, and the transformations resulting from them. Fulminic acid, which is dibasic, and unknown in the free state, is obtained in combination with oxide of silver or oxide of mercury, forming the fulminating silver and fulminating mercury, the latter of which is the material used for percussion caps, by dissolving the metal in nitric acid and adding alcohol, when a very complex reaction occurs, and the fulminating salt is formed.
With sulphur, cyanogen forms a new compound radical sulphocyanogen, CyS = CsCy, unknown in the free state. It is obtained as sulphocyanide of potassium, by melting ferrocyanide of potassium with sulphur, when each equivalent of K Cy takes up 2 eqs. of sulphur, forming the salt K, CyS₂ = K CsCy. This is purified by solution in alcohol. The radical forms also an acid with hydrogen, H, CsCy, hydrosulphocyanic acid. This acid and its soluble salts are recognised by striking a deep red colour with salts of sesquioxide of iron.
With the metals, cyanogen forms salts very similar to the chlorides. The cyanides of potassium, silver, and mercury can hardly be distinguished from the corresponding chlorides.
But cyanogen is remarkable for forming with certain metals remarkable compound radicals, which are monobasic, dibasic, and tribasic. Thus we have—
Platinocyanogen, PtCy = Cpy monobasic. Ferrocyanogen, FeCy = Cy dibasic. Ferridicyanogen, Fe₂Cy = 2 Cy = CdCy tribasic.
There are also cobaltocyanogen, CoCy, tribasic, manganocyanogen, chromocyanogen, and iridocyanogen, and two or three different platinocyanogens. Our space forbids us to enter into minute details, but we may state that 2 eqs. of ferrocyanide of potassium, 2 K Cy, Fe₂ = Cy, Fe₂K₁, when acted on by chlorine yield 1 eq. chloride of potassium, K Cl, and 1 eq. ferridicyanide of potassium Cy, Fe₂, K₁. This is a beautiful red salt, also manufactured on the large scale.
Prussian blue, a compound of cyanogen and iron, is formed either by the action of ferrocyanide of potassium on salts of sesquioxide of iron, or of ferridicyanide on salts of protoxide of iron. It is probable that there are more blue compounds than one, and that the ferrocyanogen being dibasic, forms a different compound from that produced by the tribasic feridicyanogen. The reaction with the ferrocyanide is probably this—
\[3 \text{Cy}, K₂ + 2 \text{Fe}_₂O₃ = 6 \text{KO} + \text{Cy}_₄\text{Fe}_₂ = \text{Fe}_₄\text{Cy}_₃\]
and with the ferridicyanide—
\[ \text{CdCy}, K₂ + 3 \text{FeO} = 3 \text{KO} + \text{Cy}_₄\text{Fe}_₂ = \text{CdCyFe}_₂\]
But there is still some doubt as to the precise composition of the different forms of Prussian blue.
The variety of compound radicals formed by cyanogen, especially with iron and platinum, and the beauty of the salts thus formed, which generally crystallize with great facility, render these compounds very interesting. But it is in its relations to organic chemistry that cyanogen is most important, and we shall see, that in the decomposition of organic compounds containing nitrogen, compounds of cyanogen are constantly appearing, as well as compounds derived from them by transformation, such as urea. Cyanogen generally combines with the compound organic positive radicals, such as methyle, ethyle, benzoyle, and others. The most important of these compounds will be noticed in their proper place.
Carbon and Chlorine.
These elements do not directly combine; but when various organic compounds are exposed to the combined action of sun-light and chlorine, they are gradually destroyed, their hydrogen combining with chlorine, and finally their carbon also. There are two chlorides of carbon—C, Cl₁, which has been called protoclchloride of carbon, a colourless liquid; and C₁H₂, which has been called sesquiclchloride of carbon, a crystalline solid. They are of no interest except as being the ultimate products of the substitution of chlorine for hydrogen in certain organic compounds.
The compounds of carbon with bromine and iodine are less known, but appear to be analogous to the chlorides. Carbon is not known to combine with fluorine.
9. Sulphur.
Symbol S. Equivalent = 16.
This element is found pure as a product of volcanic action, and vast quantities of it are exported from Etna, Lipari, &c. It occurs also frequently in combination with metals forming sulphurites; the principal ores of lead, copper, bismuth, antimony, and mercury, are sulphurites; and those of iron, cobalt, nickel, zinc, cadmium, tin, arsenic, molybdenum, and silver, also occur. In combination with oxygen it is found as sulphuric acid, in gypsum or sulphate of lime, and in the sulphates of baryta, strontia, and lead. Chemistry. Sulphur combined with hydrogen, or hydrosulphuric acid, is found in some mineral waters.
Sulphur is a solid of a peculiar pale yellow colour. It crystallizes easily when melted, and is found often finely crystallized. It melts about 245°, and when heated beyond 300° becomes thick and viscid, but beyond 500° it becomes again fluid, though less so than at first. At about 600° it boils, forming a brown vapour of specific gravity about 6650, which condenses on a cold surface or in water into a light powder, called flowers of sulphur. Heated in the air, it burns with a blue flame, producing a very suffocating gas, sulphurous acid. It is insoluble in water, sparingly soluble in boiling alcohol.
It exists, as has been already mentioned, in three different solid states or allotropic modifications; one in which it forms 4-sided prisms, when melted and allowed to cool; another when dissolved by the aid of heat in sulphuret of carbon, when it forms oblique octahedrons; and the third, when heated to 500° or 600° and thrown into water, when it forms a dark brown, transparent, amorphous, viscous mass, which may be drawn into threads. It is probable that there are three corresponding liquid states, the first fluid at 240° to 300°, the second viscid, from 350° to 500°, and the third again fluid, from 500° to 600°. There are probably also three forms of the gas or vapour, of different densities; at least this seems to be the case in some of its compounds.
Sulphur has a strong affinity for oxygen, but in regard to metals and hydrogen it has equally strong affinities, being negative to them, and analogous in its relations towards metals to both oxygen and chlorine.
The uses of sulphur, as a combustible for matches, as an ingredient in gunpowder, in the manufacture of sulphuric acid, and in medicine, are well known and important.
**Sulphur and Oxygen.**
These elements combine in several proportions, all the compounds being acids. But two of them are of special importance, sulphurous acid and sulphuric acid. We shall first, therefore, describe these, and then briefly notice the others.
1. **Sulphurous Acid**, $SO_2 = 32$.
This is a gas, formed whenever sulphur burns in oxygen or in air. It is colourless, transparent, of a peculiar unpleasant taste and a most suffocating smell. Its specific gravity is 2·247 nearly. It is prepared also by heating sulphuric acid with copper filings, mercury, or charcoal. In each case the sulphuric acid, $SO_3$, loses 1 eq. oxygen, which unites with the metals or the carbon. In the case of copper we have, $2(HO, SO_2) + Cu = (CuO, SO_2) + 2HO + SO_2$. With charcoal, $2(HO, SO_2) + C = 2SO_2 + 2HO + CO_2$. In the latter case, the gas is mixed with carbonic acid, and is therefore only proper for preparing the aqueous solution and the salts of sulphurous acid, the carbonic acid being excluded by the stronger sulphurous acid. Sulphurous acid gas must be collected over mercury—being absorbed by water, to which it communicates its suffocating odour.
The gas is easily liquefied by cold, under the ordinary pressure, and is kept in tubes hermetically sealed. It is a decided acid, forming salts with bases, and it has a peculiar action on vegetable blues, first reddening them, and then bleaching them. But the bleaching action differs from that of chlorine, for the colour is not destroyed, and may be restored, reddened of course, by stronger acids.
Sulphurous acid is characterized by its tendency to combine with a third equivalent of oxygen, and thus to be converted into sulphuric acid, which is manufactured in this manner, since sulphur does not combine directly with more than 2 eqs. of oxygen. The salts of this acid, sulphites as they are called, possess a considerable deoxidizing power, depriving many substances of oxygen, and being converted into sulphates.
Sulphurous acid is used in bleaching wool and silk, for which chlorine cannot be employed.
2. **Sulphuric Acid**.
a. **Anhydrous Acid**, $SO_2 = 40$.
Anhydrous or dry sulphuric acid is obtained by distilling the fuming or Nordhausen sulphuric acid, made by heating dried sulphate of iron. This fuming liquid is a compound or a mixture of anhydrous acid and of hydrated sulphuric acid, or oil of vitriol, which is the true active sulphuric acid; a gentle heat expels the anhydrous acid, which is very volatile, and collects in the receiver in the form of white crystals.
Anhydrous sulphuric acid is remarkable for its intense attraction for water. When thrown into water it hisses like red-hot iron, developing much heat, and forming oil of vitriol or hydrated acid. It is probably not a true acid, but readily passes into the true or hydrated form by the action of water. It melts at 68° and boils at 95°. It fumes strongly in the air, and attracts moisture with great rapidity. If a drop of water be allowed to fall into a bottle containing anhydrous sulphuric acid, there is a flash of light with explosion.
b. **Hydrated Sulphuric Acid**, $HO, SO_2$ or $H, SO_4 = 49$.
This, the true, active sulphuric acid, also called oil of vitriol, because it is obtained by distilling green vitriol or sulphate of iron, and has an oily consistence, is formed whenever the anhydrous acid comes in contact with water, $SO_2 + HO = HO, SO_2$. It was formerly made by distilling green vitriol or protosulphate of iron; the action of heat on that salt, dried at a moderate heat, so as to leave 1 eq. of water, is as follows: $FeO, SO_2, HO = FeO + HO, SO_2$. The protoxide of iron, $FeO$, is oxidized into sesquioxide, $Fe_2O_3$, at the expense of half of the sulphuric acid; thus $2FeO + SO_2 = Fe_2O_3 + SO_2$; so that finally sesquioxide of iron is left, and sulphurous acid is given off with the oil of vitriol.
The modern manufacturing process is far more economical and productive. Sulphur is burned in air, with the help of a little nitre. The sulphurous acid gas thus formed is conducted into a large leaden chamber, where it meets with nitrous acid, obtained by the action of starch on nitric acid, and also with the vapour of water, introduced from a boiler. Water is also present on the floor of the chamber. The resulting action is rather complex. First, sulphurous acid, nitrous or hyponitrous acid, and water, combine to form the compound $2SO_2, NO_2 + HO$. This compound forms crystals which fall down in a shower like snow, but are decomposed as soon as they touch the water on the floor, when the sulphurous acid is oxidized into sulphuric acid, and the nitrous or hyponitrous acid reduced to deutoxide of nitrogen; thus, $2SO_2, NO_2, HO = 2SO_2 + NO_2 + HO$. The Chemistry, sulphuric acid dissolves in the water; the deutoxide of nitrogen rises into the air of the chamber, in which a continual current of air is kept up, and with the oxygen of the air again forms nitrous acid, which forms, with a fresh portion of sulphurous acid and water, the same crystalline compound as before. This is again decomposed by the water, and again deutoxide of nitrogen rises, again forms nitrous acid, and again the crystals are formed and decomposed, and so on, continuously. In this way, a comparatively small amount of deutoxide of nitrogen, supplied at first as nitrous acid, oxidizes an almost unlimited quantity of sulphurous acid, acting as a carrier of oxygen from the air to the sulphurous acid. It is only because a little of the deutoxide is unavoidably lost, being carried away with the current of effluent air, that a little nitrous acid must be added from time to time to the original supply. The regular supply of air and of steam is also essential.
After this process has been continued for some time, the water on the floor of the chamber is found so strongly charged with acid, that it no longer thoroughly decomposes the crystals. It is withdrawn and replaced by fresh water. The acid liquid, which is free from nitrous acid provided an excess of sulphurous acid has been present before drawing it off, contains only sulphuric acid and water, with perhaps a little sulphurous acid. It is boiled down in vessels of glass or of platinum, to expel superfluous water, till acid begins to rise in vapour. At this point, all the water has been expelled except the one equivalent, essential, either as water or by its elements, to the existence of the hydrated acid. The liquid now boils at nearly 600°, and has a specific gravity of 1845, and an oily consistence. When pure it is colourless, but the smallest trace of any organic matter such as wood, straw, or even dust, colours it brown. It is very acid and corrosive, and has a most powerful attraction for water, the mixture of it with water developing so much heat as to break the vessel if suddenly effected. This hydrated sulphuric acid or oil of vitriol is a true acid, and in all its relations exhibits the characters belonging to hydrochloric acid, which we have called the type of acids. Like it sulphuric acid with metals forms salts, disengaging hydrogen gas, and with metallic oxides, forms the same salts, water being separated. Hence, as formerly stated, although it contains the elements $\text{SO}_3 + \text{HO}$, and may without inconvenience be regarded as a hydrate of the anhydrous acid, it is still more probable that it is really a compound of hydrogen, $\text{H}_2\text{SO}_4$, analogous in constitution to hydrochloric acid, $\text{HCl}$. All the phenomena which it exhibits with metals, oxides, &c., may be explained either way, but in the latter form its analogy with hydrochloric acid, so striking in the phenomena, becomes visible in the formula. Thus we have in the case of—
| Hydrochloric Acid | Sulphuric Acid | |------------------|---------------| | Acids, $\text{HCl}$ | $\text{H}_2\text{SO}_4$ | | Salts, $\text{MCl}$ | $\text{MO}_2\text{SO}_4$ |
The older formulae in the second column indicate no analogy with hydrochloric acid and chlorides, but in the third and fourth columns this analogy is at once evident, especially in the fourth, where $\text{Su}$ stands for $\text{SO}_3$, the hypothetical radical of sulphuric acid and sulphates. It must be borne in mind, however, that the body $\text{SO}_3$ is hypothetical and has not been proved to exist. Yet the assumption of it is generally agreed on, since it brings into one category hydrochloric acid and sulphuric acid with their respective congeners, otherwise separated. On this supposition the action of sulphuric acid on a metal and on a metallic oxide is as follows, which agrees perfectly with the action of hydrochloric acid:—
On a metal, $M + \text{H}_2\text{SO}_4 = M\text{SO}_4 + \text{H}$
On an oxide, $MO + \text{H}_2\text{SO}_4 = M\text{SO}_4 + \text{HO}$
In both cases, the metal simply replaces the hydrogen, Chemistry, and this is true of the older view also, for in that we have—
With metal, $M + \text{H}_2\text{SO}_4 = M\text{SO}_4 + \text{H}$
With oxide, $MO + \text{H}_2\text{SO}_4 = M\text{SO}_4 + \text{HO}$
We have explained this fully, because the same views apply to all hydrated acids.
Sulphuric acid forms salts with all bases, several of which occur in nature, as sulphate of lime, of baryta, of strontia, of magnesia, of lead. With 1 eq. of water it forms a hydrate, which crystallizes in cold weather. It also forms another hydrate with 2 eqs. of water, which does not crystallize so easily.
The acid is recognised by forming with baryta, whenever they meet in any mixture, the sulphate of baryta, absolutely insoluble, not only in water but also in nitric and hydrochloric acids, which dissolve many compounds of baryta insoluble in water. Any sulphate, moreover, if heated to redness with charcoal, yields, on the addition of water and acids, the odour of sulphuretted hydrogen.
The uses of sulphuric acid are numerous and important. It is employed in the manufacture of soda, bleaching powder, nitric acid, hydrochloric or muriatic acid, acetic acid, ether, alum, Epsom salt, in dissolving bone earth for agricultural purposes, in charging galvanic batteries for the electrotyping and telegraphy, and lastly, in medicine and pharmacy. When we consider that many other arts and manufactures depend on these—as for example, the making of glass and of soap, on the manufacture of soda—we shall see that the value of sulphuric acid cannot be over-estimated, and that every improvement in its preparation, or everything that renders it cheaper, will create new manufactures and new arts hereafter, as has already occurred. It is impossible to calculate what might be the effect, for example, of a great reduction in the price of sulphur, for which substance we are dependent on Sicily, and whose cheapness at present enables us to obtain sulphuric acid at a mere fraction of its former price. Such a reduction would not only cheapen sulphuric acid, but also soda, bleaching powder, glass, soap, and many other articles, and through these a multitude of products connected with them. A rise in the price of sulphur, or an interruption in the supply, such as was threatened some years ago, would have a most disastrous effect, through its influence on the price of sulphuric acid.
3. Hyposulphurous Acid, $\text{S}_2\text{O}_3 = 48$.
This acid is hardly known in the uncombined state, as it speedily undergoes decomposition. But its salts are permanent. They are formed by boiling the salts of sulphurous acid with sulphur, when 1 eq. of sulphur is taken up by 1 eq. of sulphurous acid. Thus, taking sulphite of soda, $\text{Na}_2\text{SO}_3 + S = \text{Na}_2\text{S}_2\text{O}_3$. Hyposulphite of soda thus formed, crystallizes readily in large transparent prisms. It will be seen that this acid contains sulphur and oxygen in the proportion of 1 eq. of each. But we adopt the formula $\text{S}_2\text{O}_3$ instead of $\text{SO}_3$, because, in the neutral salts, 1 eq. of the base is neutralized by $\text{S}_2\text{O}_3 = 48$, and not by $\text{SO}_3 = 24$.
The acid may be viewed either as directly formed of $\text{S}_2$ and $\text{O}_3$, or as composed of sulphurous acid and sulphur, $\text{SO}_3 + S$. The latter may probably be true, as there are several acids apparently of analogous constitution.
The most remarkable character of this acid, or rather of its salts is their power of dissolving the compounds of silver which are insoluble in water and in strong acids, such as chloride, bromide, iodide, &c., of silver. The solution thus obtained has a most intensely sweet taste, followed by a metallic aftertaste. On account of this solvent power, hyposulphite of soda is much used in photography, to fix the image by removing the compound of silver unacted on by light, which if left would be acted on and destroy the pictures. 4. Hyposulphuric Acid. \( S_2O_3 = 72 \).
This acid is more permanent. It is formed when sulphurous acid is made to act on peroxide of manganese, a portion of the acid being oxidized to sulphuric acid, which with another portion of sulphurous acid forms the new acid, for \( SO_2 + SO_3 = S_2O_3 \). The acid thus formed combines with the protoside of manganese. The action is as follows:
\[-2SO_2 + MnO_2 = MnO_2S_2O_3.\]
From the salt of manganese, others may be obtained, and from the hyposulphate of baryta, the base being removed by sulphuric acid, the acid is obtained. It is sour and tolerably permanent, unless strongly heated, but of little interest hitherto.
There are still three acids formed of sulphur and oxygen. They all contain, like the last-named acid, 5 eqs. of oxygen, with regularly increasing quantities of sulphur, and their names and formulae are—
1. Monosulphuretted hyposulphuric acid, \( S_2O_3 = 88 \) 2. Bisulphuretted hyposulphuric acid, \( S_2O_3 = 104 \) 3. Trisulphuretted hyposulphuric acid, \( S_2O_3 = 120 \)
They all form crystallizable salts with baryta, and may be obtained from these by means of sulphuric acid, which precipitates the baryta. They are sour, and easily decomposed, yielding sulphuric acid, sulphurous acid, and sulphur. They very much resemble one another, and are of no practical interest, so that we shall not describe their preparation. It is remarkable that the third of them is polymeric with hyposulphuric acid, but the two acids are quite distinct; for not only can the acid \( S_2O_3 \) be obtained in solution, while the acid \( S_2O_3 \) is not known in a separate state, but they neutralize totally different weights of the same bases, or equal weights of the base require different weights of the two acids, in the proportion of 120 to 48.
**Sulphur and Hydrogen.**
These elements form two compounds, one of which is of great importance to the chemist. It is—
1. Hydrosulphuric Acid, \( HS = 17 \).
This compound, called also sulphuretted hydrogen, is a gas which sometimes occurs in volcanic districts, and is frequently found dissolved in mineral waters. It is formed during the putrefaction of organic matters containing sulphur, such as albumen in eggs, &c.
It is procured by the action of acids on sulphuretted iron; thus, with sulphuric acid,
\[ FeS + H_2SO_4 = FeSO_4 + H_2S; \]
and with hydrochloric acid,
\[ FeS + HCl = FeCl_2 + H_2S. \]
It is also produced by the action of hydrochloric acid on ter-sulphuret of antimony,
\[ SbS_3 + 3HCl = SbCl_3 + 3H_2S. \]
It may be collected over warm water or brine; cold water absorbs it.
It is transparent, inflammable, burning with a pale blue flame, and depositing sulphur. It has a most offensive smell, that in fact of putrid eggs, which yield it, and this smell it communicates with its sulphureous taste to water, as in the water of Harrowgate. It also blackens the salts of lead and of many other metals, forming sulphurets of the metals. The action with a salt of lead is as follows—if we suppose the lead to be present as oxide, the acid may be left out of view;
\[ PbO + HS = HO + PbS. \]
It is the same whether the lead be present as chloride, \( PbCl \), or as sulphate, \( PbSO_4 \), or as carbonate, \( PbCO_3 \).
It is this action of hydrosulphuric acid on metals and their salts which renders it so valuable as a test; for as the sulphures of the heavy metals are insoluble in water, and usually of dark colours, it enables us to detect a very small quantity of those metals on the solutions of which it acts, and even to distinguish many of them by the colour of the precipitate. The salts of lead, copper, mercury, silver, gold, bismuth, and some others, form dark brown or black sulphures; protosalts of tin give a chestnut brown; antimony, an orange-brown; persalts of tin, a dirty-yellow; arsenic and cadmium, a bright yellow, with this gas.
The solution of the gas reddens vegetable blues, but as in the case of carbonic acid, on standing or on boiling the blue colour returns.
The gas is liquefied by a powerful pressure. It is highly poisonous when inhaled, and has often caused fatal accidents in graves, when, a neighbouring coffin being perforated by the pickaxe, the gas rushes out and fills the grave, striking down the gravedigger like lightning. The same thing happens in the large cloacae of great cities. It is said that a horse whose head is in pure air, while his body is enclosed in an atmosphere containing only \( \frac{1}{6} \) th of its volume of the gas, is soon killed by the gas absorbed through the skin. Taken internally, it is not only safe, but a useful remedy.
2. Bisulphuret of Hydrogen, \( HS = 33 \).
This compound is formed when lime and sulphur are boiled with water, till a deep yellow solution is formed. This is then poured into hydrochloric acid of moderate strength. The liquid becomes milky, and on standing deposits the bisulphuret as a heavy oily liquid, which may be withdrawn by a pipette. It undergoes spontaneous decomposition, which is hastened by the presence of metallic oxides. In these characters, and in its composition, it is analogous to the deutoxide of hydrogen. It has a pungent and offensive smell. When sealed up in one end of a bent tube, and left to itself, it is gradually resolved into sulphuric and hydrosulphuric acid, and the latter is liquefied at last by its own pressure.
There is said to be a compound of sulphur and nitrogen, \( NS_2 \), a yellowish white powder. But this is doubtful.
**Sulphur and Chlorine.**
When dry chlorine is passed over sulphur they readily unite and form two compounds, both liquid, volatile, and pungent. One is \( SCl \), subchloride or dichloride of sulphur, a dense yellow liquid of specific gravity 1687, boiling at 280°. The other is \( SCl_2 \), protocloride of sulphur, a red liquid, of specific gravity 1620, boiling at 150°. Both decompose water, forming hydrochloric, sulphuric, and sulphurous acids.
When sulphur and iodine are heated together, they melt and form a black crystalline mass on cooling. It cannot be distilled, heat decomposing it, and its precise composition is unknown. Nothing is known of the compounds of bromine and sulphur, nor of those of fluorine with sulphur.
**Sulphur and Carbon.**
When the vapour of sulphur is made to pass over charcoal at a red-heat, a compound is formed which passes over and is collected in water where it sinks as a heavy liquid to the bottom. To purify it from a little sulphur that distils along with it, it is distilled again at a gentle heat. Its composition is \( CS_2 \), bisulphuret of carbon.
It is a very mobile, transparent, colourless liquid, refracting light strongly, of a very peculiar odour, like that of decaying cabbage or horse-radish, very inflammable. Its specific gravity is 1293, and it boils at 118°. Bisulphuret of carbon is a powerful solvent for many substances insoluble in water or alcohol; such as phosphorus, sulphur (which crystallizes beautifully from the solution), resins; and even such bodies as caoutchouc and gutta percha are softened if not dissolved by it. It is now manufactured on the large scale, and is used in making varnishes and certain preparations of caoutchouc.
10. Selenium.
Symbol Se. Equivalent = 39.5.
This element is so closely analogous to sulphur, that a very brief account of it will suffice. It occurs in nature chiefly as seleniuret of lead, a rare mineral. Some kinds of iron pyrites contain a little seleniuret of iron, or at all events a compound of selenium; and when sulphur made from such pyrites is converted into sulphuric acid, there is found in the leaden chambers a deposit consisting of sulphur, several metals, such as copper, lead, and arsenic, and selenium. From this deposit, or from the native seleniuret of lead, selenium is prepared. It is first dissolved in the form of selenious acid, and this is deoxidized by sulphurous acid, when the selenium separates as a deep red powder. At 392° it melts, forming a brown liquid, which boils at about 1290°, and yields a deep yellow gas. On cooling, the liquid first becomes viscid and tenacious, and finally consolidates to a nearly black solid mass, which in thin layers is translucent and red, and has a metallic lustre. When sublimed, the vapour condenses on a cold surface into a powder of a fine red, similar to the precipitated selenium.
In all its chemical relations selenium resembles sulphur, only that it is denser, its specific gravity being 4280 in the mass and 4800 in the powder; and less volatile. Its affinities are also less powerful.
Selenium appears to form three compounds with oxygen, namely, the oxide of selenium, a gas, the composition of which is not known, selenious acid $\text{SeO}_2$, and selenic acid $\text{SeO}_3$.
Heated in air, selenium burns with a pure blue flame, producing a very penetrating and peculiar odour, compared to that of putrid horse-radish. This belongs to the oxide, which has not been obtained in a state of purity. A very minute trace of selenium may be detected before the blowpipe by this character. The gas appears to be poisonous.
Selenious acid, $\text{SeO}_2$, is the chief product of the combustion of selenium, and if the operation is conducted in oxygen in a proper apparatus, the acid collects in the cold part of it in colourless crystals, very soluble in water. This acid is also formed when selenium is oxidized by nitric or by nitro-hydrochloric acids. Selenious acid is deprived of its oxygen by many substances, such as iron, zinc, or sulphurous acid, when the selenium is deposited as a cinnabar red powder. The vapour of the acid is yellow.
Selenic acid, $\text{SeO}_3$, or, in the state of hydrate, $\text{HO}_2\text{SeO}_3 = \text{H}_2\text{SeO}_4$, is entirely analogous to sulphuric acid in properties. It is obtained in combination with oxide of lead, by heating seleniuret of lead with nitrate of potash; or by first heating selenium with that salt, which forms seleniate of potash, and then adding to the solution of the potash salt a salt of lead, when seleniate of lead is precipitated. This salt, $\text{PbO}_2\text{SeO}_3$, is decomposed by hydrosulphuric acid as follows: $\text{PbO}_2\text{SeO}_3 + \text{HS} = \text{PbS} + \text{HO}_2\text{SeO}_3$; thus yielding the hydrated acid. The anhydrous selenic acid is unknown.
The salts of selenic acid are in form and properties so exactly similar to those of sulphuric acid, as only to be distinguishable from them by analysis.
With hydrogen, selenium forms a gaseous acid, hydro-selenic acid, $\text{HSe}$, of a most fetid odour, and still more poisonous than hydrosulphuric acid. It is obtained, like hydrosulphuric acid, by the action of hydrochloric acid on a compound of iron with selenium. $\text{HCl} + \text{FeSe} = \text{FeCl} + \text{HSe}$. This gas is soluble in water, and acts on metallic solutions in the same way as hydrosulphuric acid, only forming seleniurets instead of sulphurets. $\text{MO} + \text{HSe} = \text{HO} + \text{MSe}$, is a general equation representing the action of hydroselenic acid on metallic protoxides.
Like sulphur, selenium combines directly with metals, when heated with them.
From its great rarity, selenium is not applied, either itself or in its compounds, to any useful purpose. It is probable, however, that some of its compounds, from their energetic action on the system, may prove valuable remedies.
The metallic lustre of compact selenium has led some to class it with metals. But it is a nonconductor of heat and electricity, and so analogous to sulphur, that these elements must be considered together. A third substance belongs to the same group by its chemical relations, namely tellurium; but that element has the conducting power as well as the lustre of metals, and it is regarded as a metal.
11. Phosphorus.
Symbol P. Equivalent = 32.
This element is found chiefly in the animal kingdom, in bones, as phosphoric acid united to lime and a little magnesia. But all the phosphate of lime, or bone earth of animals, is derived from their food, and consequently from the soil. In fact, all fertile soils contain this phosphate in small but essential quantity. Without it, although all the other elements of plants were present, no plant could grow. Phosphate of lime is found in minute crystals scattered through all rocks, and there are occasionally beds containing large quantities of bone earth, derived from the bones of extinct animals; as the ostolite of the Rhine, and the so-called coprolite beds in the Suffolk Crag. Phosphoric acid also occurs sparingly, combined with the oxides of lead, copper, uranium, and iron.
Phosphorus is obtained from bones, by first burning them to destroy the animal matter. The bone earth is next bruised, and digested with sulphuric acid and water till all coarse grains have disappeared, and a uniform fine powder, sulphate of lime, is formed. The water now holds in solution acid phosphate of lime.
This is filtered from the sulphate, evaporated to the consistence of a syrup, mixed with charcoal, and exposed to a white heat in a retort. The charcoal deprives the phosphoric acid of oxygen, and while carbonic acid escapes, phosphorus distils over, and is collected under water. To purify it, it is melted under water and squeezed through leather. It is then, if necessary, redistilled by itself, and kept under water.
It is a solid, nearly colourless, translucent, of the consistence of wax, fusible a little above 100°, and taking fire in air at that temperature. It boils at 550°. The specific gravity of phosphorus is 1770, water = 1000. That of its vapour is 4326, air = 1000.
It is distinguished by its inflammability, which is such, that if exposed, dry, to air, in warm weather, it often takes fire spontaneously, and is therefore kept under water. When exposed to light, it becomes opaque externally, and the change spreads gradually inwards.
When heated, it burns with great splendour, whether in air or oxygen, especially in the latter; in burning, it forms phosphoric acid, which, if no moisture be present, condenses to a white powder like snow.
When phosphorus is heated for some time short of its boiling point, between 445° and 480°, it becomes dark Chemistry. red, comparatively infusible, far less inflammable, and insoluble in sulphuret of carbon, which dissolves ordinary phosphorus. The red modification does not melt nor take fire, even at 480°. At about 500° it passes into ordinary phosphorus. This is a most remarkable instance of allotropic modification of an element, which in these two states exhibits properties, both physical and chemical, more different than are those of many different elements. Yet the one form passes into the other, and both yield the same compounds.
**Phosphorus and Oxygen.**
The affinity of phosphorus for oxygen is very strong, so that even at ordinary temperatures it is slowly oxidized in the air, becoming luminous in the dark. The temperature also rises slightly, and in summer the oxidation is thereby so much accelerated that heat enough is evolved to melt and set fire to the phosphorus. This is a true case of spontaneous combustion, and illustrates the occurrence of that phenomenon in powdered charcoal, or in porous bodies moistened with oil. At any season it may be illustrated in phosphorus, by allowing a few drops of a solution of phosphorus in bisulphuret of carbon to dry up on blotting paper, on which it leaves a film of finely divided phosphorus. This very soon begins to oxidize, vapours rise from it luminous in the dark, it gradually becomes warm, and in a few minutes bursts into flame. It has recently been proved by Schönbein that phosphorus in air first causes the formation of ozone, which is an allotropic form of oxygen, and possibly also of a hydrate of this substance, having the composition $\text{HO}_3 = \text{O}_2 + \text{HO}$. Both of these forms of ozone are much more powerful oxidizing agents than ordinary oxygen, and it appears that it is ozone which really oxidizes phosphorus, when exposed to air till the temperature rises so high as to cause combustion.
1. **Phosphorous Acid**, $\text{PO}_3 = 56$.
This acid is formed when phosphorus undergoes slow oxidation. It is best obtained pure by the action of water on terchloride of phosphorus, $\text{P Cl}_3 + 3 \text{HO} = 3 \text{H Cl} + \text{PO}_3$. It is very soluble and sour, and may be obtained in a mass of deliquescent crystals of the hydrated acid, $\text{PO}_3 \cdot 3 \text{HO}$. When heated, it yields phosphuretted hydrogen gas, while phosphoric acid is left; thus, $4 \text{PO}_3 + 3 \text{HO} = 3 \text{PO}_4 + \text{PH}_3$. Phosphorous acid is not of much importance. It tends, by combining with 2 eqs. of oxygen, to form phosphoric acid.
2. **Phosphoric Acid**.
a. **Anhydrous Phosphoric Acid**, $\text{PO}_4 = 72$.
This compound is formed when phosphorus is burned in dry air or oxygen, and appears as a snow-white substance, which must be instantly sealed up hermetically, otherwise it attracts moisture from the air, and deliquesces into the Chemistry, monobasic hydrated acid, $\text{PO}_4 \cdot \text{HO}$.
It is doubtful whether the anhydrous acid be really an acid. It cannot be tested without bringing it in contact with water on the tongue, when it instantly forms the hydrated or true acid. It is used in research on account of its tendency to abstract the elements of water from many organic substances, without charring them as sulphuric acid does.
b. **Hydrated Phosphoric Acid**.
1st, **Monobasic**, $\text{PO}_4 \cdot \text{HO}$ or $\text{PO}_4 \cdot \text{H} = 81$.
This acid is formed when the anhydrous acid acts on water. It is apt to pass into the bibasic and tribasic forms, by taking up more water, but is again obtained pure by heating to low redness, when the monobasic acid is left. It is very sour, coagulates albumen, and causes a white precipitate in nitrate of silver, the monobasic phosphate of silver, $\text{PO}_4 \cdot \text{Ag O}$ or $\text{PO}_4 \cdot \text{Ag}$. It forms only one series of salts, containing one eq. of base or of metal, hence its name. Its solution passes, slowly in the cold, rapidly when heated, first into the bibasic, and then into the tribasic form.
2d, **Bibasic Phosphoric Acid**, $\text{PO}_4 \cdot 2 \text{HO}$ or $\text{PO}_4 \cdot \text{H}_2 = 90$.
This acid is obtained by heating the solution of the tribasic or common phosphoric acid till only 2 eqs. of water are left, or by decomposing bibasic phosphate of lead or silver by hydrosulphuric acid. Its solution is not permanent, passing into the tribasic acid. But its salts are quite permanent. It does not coagulate albumen, nor precipitate nitrate of silver, unless ammonia or some base be added, when it forms a white bibasic phosphate of silver, quite different from the monobasic salt. It forms two series of salts, those with two eqs. of fixed base, such as bibasic phosphate of soda, $\text{PO}_4 \cdot 2 \text{Na O}$ or $\text{PO}_4 \cdot \text{Na}_2$, and those with 1 eq. of fixed base, and 1 eq. of basic water, as the acid bibasic phosphate of soda, $\text{PO}_4 \cdot \text{Na O}, \text{HO}$ or $\text{PO}_4 \cdot \text{Na H}$.
3d, **Tribasic Phosphoric Acid**, $\text{PO}_4 \cdot 3 \text{HO}$ or $\text{PO}_4 \cdot \text{H}_3 = 99$.
This is the common form of phosphoric acid, as the others, by taking up water, pass into it. It does not coagulate albumen, nor precipitate nitrate of silver, till some base is added, when it forms a lemon-yellow precipitate of tribasic phosphate of silver, $\text{PO}_4 \cdot 3 \text{Ag O}$ or $\text{PO}_4 \cdot \text{Ag}_3$. It forms 3 series of salts, with 3 eqs. of fixed base, as the salt of silver just named; with 2 of fixed base and 1 of water, as in common phosphate of soda, $\text{PO}_4 \cdot 2 \text{Na O}, \text{HO}$ or $\text{PO}_4 \cdot \text{Na}_2 \cdot \text{H}$; and with 1 eq. of fixed base and 2 of water, as the acid phosphate of potash, $\text{PO}_4 \cdot \text{KO}, 2 \text{HO}$ or $\text{PO}_4 \cdot \text{K}_2 \cdot \text{H}_2$. This is the form of the acid existing in bones, and in the mineral kingdom.
It will be seen, that if we regard these acids as hydrates or compounds of water with dry acid, they all contain the same acid, and differ only in water. This is possible, for in sulphuric acid we have oil of vitriol, $\text{SO}_4 \cdot \text{HO}$, the hydrate $\text{SO}_4 \cdot 2 \text{HO}$, and the hydrate $\text{SO}_4 \cdot 3 \text{HO}$, all of which undoubtedly contain the same acid, and yield the same salts with bases, namely, sulphates, of which there is but one class or series.
But the three phosphoric acids differ far more than is accounted for by mere differences in the proportion of water, as in their action on albumen, and on nitrate of silver, and above all, in forming salts entirely distinct, which are monobasic, bibasic, and tribasic, that is, contain 1, 2, or 3 eqs. of base, fixed or otherwise. Nothing of all this occurs in the different hydrates of sulphuric acid, the first of which is the true acid, $\text{H}_2\text{SO}_4$, as already explained, the other two compounds of this with water, $\text{H}_2\text{SO}_4 \cdot \text{HO}$ and $\text{H}_2\text{SO}_4 \cdot 2 \text{HO}$. But this water in these two compounds is not basic, and is not replaceable by bases.
What is the cause of this difference between sulphuric Chemistry, and phosphoric acid? It is not enough to say, that when the dry acid is combined with 1, 2, or 3 eqs. of water, it is disposed to take up 1, 2, or 3 eqs. of base. That is the fact to be explained, and not an explanation of it. Sulphuric acid exhibits no such tendency when combined with 2 or 3 eqs. of water, and we can hardly suppose the three phosphoric acids to contain the same acid.
Now, here the hydrogen theory of acids comes to our aid. According to it, the first hydrate is PO₄H like nitric acid, NO₃H. It takes 1 eq. of base to form neutral salts, because it contains 1 eq. of replaceable hydrogen, as sulphuric and nitric acids do.
The second hydrate is PO₄H₂. Here the radical is different, and as there are 2 eqs. of replaceable hydrogen, it takes 2 eqs. of base to form neutral salts. And there are two series of these, according as half or the whole of the hydrogen is replaced by metals.
The third hydrate, in like manner, is PO₄H₃, with a different radical, and requiring 3 eqs. of base for the 3 eqs. of replaceable hydrogen, forming also 3 series of salts, according as the hydrogen is partially or entirely replaced by metals.
On this view, the three acids must be different, whereas, on the other, they ought to be the same, as in sulphuric acid. We see also why they form different salts, and why the first can form only one series, the second two, and the third three series of salts.
Phosphoric acid as such is not much used nor of much interest, but its salts, especially those of the tribasic modification, are of the utmost and most essential importance. The earth of bones is essentially a tribasic phosphate of lime; the principal salt in the blood, to which it owes its alkaline reaction, and its peculiar power of absorbing and of giving off carbonic acid, is a tribasic phosphate of soda, with 2 eqs. of fixed base and 1 eq. of basic water, PO₄K₂HO₃ or PO₄Na₂H₂O₃, and the chief salt in the juice of flesh, and in the gastric juice, that which gives the acid reaction to these fluids, is a tribasic phosphate of potash, with 1 eq. of fixed base and 2 eqs. of basic water, PO₄K₂HO₃ or PO₄Na₂H₂O₃.
Since these peculiar phosphates have undoubtedly each its own peculiar function to perform in the animal economy, we see how important it is to study the most minute and apparently trifling peculiarities of such a compound as tribasic phosphoric acid; although these very researches, when first made, were regarded as scientific curiosities of no practical value. No one could have conjectured that it would ever be important to know that tribasic phosphoric acid with soda tends to form a salt with 2 eqs. of fixed base, of alkaline properties, though its composition is that of an acid salt, while the same acid with potash forms by preference a salt with 1 eq. of fixed base which is strongly acid, while yet the acid can form two other compounds with each alkali. Yet we now see that such apparently insignificant facts are closely connected with the due performance of the most essential vital functions. In hundreds of cases we can substitute potash for soda, and obtain the same results, but potash cannot replace the soda of the phosphate in the blood, nor soda the potash of that in the juice of flesh.
3. Hypophosphorous Acid, PO₄ = 40.
This acid is formed when phosphorus is boiled with bases, such as lime or potash. Phosphoric acid and phosphuretted hydrogen are formed at the same time, as will be shown under phosphuretted hydrogen, and the two acids both combine with the base. The phosphate of lime is insoluble, the hypophosphite soluble. The acid is little known, but has a tendency to absorb oxygen and pass into phosphoric acid.
Phosphorus and Hydrogen.
1. Phosphuretted Hydrogen Gas. PH₄ = 35.
This compound is formed when phosphorus is boiled with lime and water, or potash and water. The precise nature of the reaction is not ascertained, so as to enable us to represent it in an equation; but water is decomposed, and while its oxygen unites with one portion of phosphorus to form hypophosphorous acid, and apparently with another to form phosphoric acid, its hydrogen combines with a third portion, forming the new compound, which is given off in the form of a gas, not absorbed by water.
It is highly inflammable, and when prepared as above takes fire spontaneously in contact with air. But this property is owing to the presence of a minute quantity of another compound of the same elements, the liquid phosphuretted hydrogen; and when this is removed, the gas is no longer spontaneously inflammable, though still taking fire when slightly heated in air. The spontaneously inflammable gas loses that property by standing over water, when it deposits a little of a solid phosphuretted hydrogen, formed from the liquid one.
Each bubble of the spontaneously inflammable gas, as it rises through the water, takes fire, and forms a beautiful ring of white vapour (water and phosphoric acid), which expands as it ascends. Bubbles of the gas, allowed to enter a vessel of oxygen, produce each of them a slight explosion and a brilliant flash of light, but care must be taken that only one bubble at a time enters the oxygen, otherwise dangerous explosions may occur. The gas may also be prepared by the action of phosphuretted calcium on water.
When phosphuretted calcium is acted on by dilute-hydrochloric acid, or when phosphorus is boiled with an alcoholic solution of potash, the pure gas is formed, not spontaneously inflammable. All substances which destroy the liquid phosphuretted hydrogen, such as alcohol, ether, and volatile oils, deprive the spontaneously combustible gas of that property. And the addition of a minute trace of the liquid compound to the non-spontaneously inflammable gas renders it at once spontaneously inflammable.
2. Liquid Phosphuretted Hydrogen. PH₄ = 34.
When the spontaneously inflammable gas is passed through a U-shaped tube surrounded by a freezing mixture, it deposits water which freezes, and a small quantity of the liquid compound, PH₄. The gas has now lost its spontaneous inflammability. The liquid instantly takes fire in contact with air or oxygen. When kept the liquid is resolved into the gas PH₄, and a solid compound P₂H₄, thus, 5 PH₄ = 3 PH₄ + P₂H₄.
3. Solid Phosphuretted Hydrogen, P₂H₄ = 65.
The formation of this compound from the liquid one has just been explained. It is deposited from the spontaneously inflammable gas when kept over water, as an orange-coloured film.
It should be mentioned that the gas, PH₄, has a composition analogous to that of ammonia, NH₄, and that it has also some analogy in properties. Thus it seems to be a weak base, and with hydroiodic acid it forms a saline compound crystallizing in cubes, like the hydriodate of ammonia. The phosphuretted hydrogen also, like ammonia, admits of the replacement of its hydrogen by such radicals as methyl and ethyl, forming volatile bases, analogous to the volatile organic bases derived from ammonia.
With nitrogen phosphorus forms a compound, PN₄, a white solid, which resists a red heat and the action of the strongest acids.
Phosphorus and Chlorine.
1. Terchloride of Phosphorus, PCl₃ = 138·5.
When chlorine comes in contact with phosphorus, the latter takes fire, and they combine. If the phosphorus be in excess, we obtain a colourless liquid, PCl₃. It is pungent, fuming, of specific gravity 1450. When mixed with Chemistry. Water it sinks to the bottom, and there is rapidly dissolved heat being developed. The action is as follows: \( \text{PCl}_3 + 3 \text{HO} = 3 \text{HCl} + \text{PO}_4 \). The hydrochloric acid dissolves in the water along with the phosphorous acid, but may be expelled by a gentle heat, and hydrated phosphorous acid is left.
2. Perchloride of Phosphorus. \( \text{PCl}_5 = 209.5 \).
When the chlorine is in excess, or when chlorine is passed through the last compound, there is formed the solid perchloride, \( \text{PCl}_5 \). This also decomposes water, as follows: \( \text{PCl}_5 + 5 \text{HO} = 5 \text{HCl} + \text{PO}_4 \), yielding, therefore, hydrochloric and phosphoric acids.
Perchloride of phosphorus has of late been employed as an agent of research in organic chemistry. By its means, certain anhydrous organic acids, previously unknown, have been obtained, and much light thrown on the constitution of organic acids.
Phosphorus combines instantly with iodine, heat and light being evolved. The compounds are of a dark red or brown colour, and solid. They decompose water exactly as the chlorides do. It is probable that there are two iodides, \( \text{PI}_3 \) and \( \text{PI}_5 \), corresponding to the chlorides, but the former alone has been analysed, and another iodide, \( \text{PI}_5 \), has also been obtained. These two compounds may be had in orange and in dark red crystals by dissolving phosphorus and iodine in bisulphuret of carbon, and applying artificial cold.
Bromine acts very violently on phosphorus, and seems to form bromides corresponding to the chlorides.
No compounds are known of phosphorus with fluorine or carbon.
With sulphur, phosphorus readily combines in several proportions. The compounds are not only highly inflammable, but liable to explode with great violence when slightly warmed, and sometimes even spontaneously. Hence they are very dangerous, and must be very cautiously experimented with. Berzelius, who examined them, narrowly escaped from some frightful explosions, occurring quite unexpectedly. Some of them are liquid, others solid; and it appears that the different allotropic states of both the elements are seen also in these compounds, several of which are isomeric. As these compounds are not fully understood, and are for the present of no practical importance, we shall not enter into details in regard to them.
12. Boron.
Symbol B. Equivalent = 10.9.
This element is found in nature combined with oxygen, as boracic acid, which occurs free, dissolved in the vapours of certain volcanic districts in Tuscany. The hot vapours are received in reservoirs of water, in which the acid dissolves, and the heat of the vapours is employed to evaporate the water, till at last the acid crystallizes nearly pure. In Thibet boracic acid occurs in the soil near certain lakes, combined with soda, forming the crude borax of commerce, which is purified from the peculiar fatty matter it contains by a secret process known only to the Dutch. Borax is now largely manufactured in England, from the boracic acid of Tuscany, and of the volcanic islands of the Mediterranean.
Boron is obtained by heating dry boracic acid with potassium, \( 4 \text{BO}_3 + K_2 = 3 (\text{KO}, \text{BO}_3) + \text{B} \). Water dissolves the borate of potash, and leaves the boron as a dark brown infusible powder, which, when heated to redness in oxygen, burns and reproduces boracic acid.
\[ \text{Boracic Acid, BO}_3 = 34.9. \]
Obtained as above described, and purified by repeated crystallization, or from borax (hiborate of soda) by the addition of sulphuric acid to a hot saturated solution, forms white scaly crystals, composed of the anhydrous acid and water, \( \text{BO}_3, 3 \text{HO} \). When heated the crystals melt, lose their water, and at a red heat leave the anhydrous acid perfectly fluid, which on cooling forms a transparent glass. This soon becomes opaque by attracting water from the air. The acid is very soluble in hot, sparingly soluble in cold water. It is a weak acid at ordinary temperatures, but at a red heat it expels all less fixed acids. It gives to all its compounds a peculiar tendency to melt when heated, and hence borax is much used as a flux in metallurgical operations on the small scale. Boracic acid, and the compounds of boron in general, colour flame green, and by this character the presence of boracic acid has been detected in various minerals in which it is present in small quantity, as in tourmaline and schorl, &c. Boracite and adalbite contain boracic acid in larger proportion. There is no other compound of boron and oxygen.
With chlorine boron forms a gaseous compound, the terchloride, \( \text{BCl}_3 \), corresponding to boracic acid, which decomposes water, yielding boracic and hydrochloric acids, \( \text{BCl}_3 + 3 \text{HO} = 3 \text{HCl} + \text{BO}_3 \).
With fluorine it forms a similar gas, terfluoride of boron, \( \text{BF}_3 \), which fumes strongly in moist air. Its action on water is as follows: \( 3 \text{BF}_3 + 3 \text{HO} = (3 \text{HF}, 2 \text{BF}_2) + \text{BO}_3 \). The compound \( 3 \text{HF}, 2 \text{BF}_2 \) is called hydrofluoboric acid.
With nitrogen boron is said to form a white solid compound, \( \text{BN} \), which is very stable. When fused with hydrate of potash it is converted into boracic acid and ammonia, the latter being expelled, while the former combines with the potash. \( \text{BN} + 3 \text{KOH} = \text{KO}, \text{BO}_3 + 2 \text{KOH} + \text{NH}_3 \).
The chief uses of boracic acid are as a flux, both in itself and in the form of borax; and the latter substance is also used in medicine. Goldsmiths use borax to clean the surface of gold, silver, and other metals which are to be soldered together. Borax is sprinkled on the metal, and melted by the blowpipe, when it dissolves any oxide or other impurities, leaving a bright metallic surface.
13. Silicon or Silicium.
Symbol Si. Equivalent = 21.3.
Next to oxygen, this is perhaps the most abundant element. Its only oxide, silicic acid or silica, constitutes, whether free or combined, by far the greater part of all rocks and soils, excepting only the different forms of limestone, marble, and chalk, gypsum, and rock salt.
Silicon is obtained by the action of potassium on a compound of fluorine, silicon, and potassium; and appears, like boron, in the form of a dark brown powder, which, strongly heated in oxygen, burns with a brilliant light, and is converted into silicic acid. It has recently been stated that, by means of a galvanic current, silicon has been deposited on the surface of metals, and exhibits a bright metallic lustre. This requires confirmation.
\[ \text{Silicon and Oxygen, SiO}_3 = 45.3. \]
This, the most abundant of all minerals, occurs pure in the form of rock crystal and quartz; which is either crystallized in six-sided prisms, terminated by six-sided pyramids, or compact and massive. Many kinds of sandstone are also nearly pure silicic acid, or silica, as it is often called. With very small quantities of oxide of iron and other metals, it forms agate, calcedony, jasper, carnelian, bloodstone, and many other ornamental stones. In amethyst there is only a trace of manganese. In opal there is hardly any impurity; and flint is also very nearly pure silicic acid. The deposits and rocks known by the names of mountain meal, polishing slate, kieselguhr, &c., are also pure silicic acid, in the form of the exuviae or shells of the diatomaceæ, microscopic organisms which abound in almost all natural waters.
Felspar, which is an ingredient of almost all rocks, is a compound of silicic acid, alumina, and potash; and there are few other minerals occurring in rocks which are not also Chemistry. Silicates. This is the case with mica, hornblende, talc, serpentine, hypersthene, &c.; while porphyry, slate rock, granite, and many others, such as basalt, trap rocks, and lavas, are chiefly modifications of felspar. The simple minerals found crystallized in nodules and veins in all rocks, such as zeolites and the like, are also in most cases silicates.
Silicic acid exists dissolved in sea-water and in all natural waters, although in small proportion, as is proved by the existence and rapid development of the siliceous shelled diatomaceae in all such waters. Flint has probably been originally in the form of these minute organisms, for it often contains them unaltered. Some springs, especially thermal springs, contain much dissolved silica, as, for example, the Geysers of Iceland.
Pure silicic acid is easily obtained by simply pulverizing rock crystal or white quartz. From impure quartz, or siliceous sand or minerals, it is obtained by fusion with three parts of potash, when a glass is formed, soluble in water. The addition of acids to the strong solution causes the silica to separate as a bulky jelly; if added to the very dilute solution, the silica remains dissolved; but on evaporation to a certain point gelatinizes. The jelly is dried up to a powder, and then the silica becomes absolutely insoluble in water and acids, except hydrofluoric acid. All soluble matter being washed away with the aid of acid, the silica remains as a powder, gray and translucent while moist, snow-white and opaque when dry. However finely divided, it is always gritty to the teeth. Although thus expelled from its salts at ordinary temperatures by almost all acids, at a red heat it expels in its turn all that are volatile at that temperature. With the alkalies it forms glass, soluble when the alkali is in excess, insoluble or ordinary glass when the silicic acid predominates.
The uses of silica are numerous. It is an essential constituent of plants, more especially of the graminées, cerealia, and rush, cane, or bamboo tribes. It is employed in the manufacture of glass, and in the form of sand, for building mortar. It is also used along with lime, with which it forms a fusible silicate, as a flux in smelting metals, especially iron. Many forms of it are valued as ornamental stones, of which the opal is the most precious, from its rarity and beauty.
With chlorine, silicon forms a volatile fuming liquid, trichloride of silicon, SiCl₃, which decomposes water in the same way as trichloride of boron, SiCl₃ + 3 HO = 3 HCl + SiO₂.
With fluorine it forms a gaseous tetrafluoride, SiF₄. This acts on water like the tetrafluoride of boron, producing a hydrofluosilicic acid. 3 SiF₄ + 3 HO = (3 HF, 2 SiF₄) + SiO₂. The hydrofluosilicic acid (3 HF, 2 SiF₄) forms with potash and soda insoluble double salts, as, for example, in this reaction: 3 HF, 2 SiF₄ + 3 KO = 3 KF, 2 SiF₄ + 3 HO. The new salt, 3 KF, 2 SiF₄, may be regarded as a compound of fluoride of potassium with tetrafluoride of silicon.
It is in consequence of the great tendency of silicic acid to form the tetrafluoride with hydrofluoric acid, that the latter acid corrodes glass and porcelain. But the tetrafluoride of silicon may be prepared in glass vessels, by heating a mixture of fluor-spar, fine sand, and sulphuric acid. The sand is dissolved and the glass escapes. The tetrafluoride being made to pass through water decomposes it as above explained, forming hydrofluosilicic acid and silicic acid. The latter separates as a jelly, which would soon block up the tube, if we did not protect it by causing the end of it to dip just under the surface of mercury, by which means no water reaches the tube. The liquid is strained off from the jelly, and used as a test for potash and baryta. The jelly when dry forms a fine light bulky powder of silicic acid. If the liquid and the jelly be evaporated together, the tetrafluoride is reproduced, and the whole disappears.
METALS.
This numerous class of elements is characterized by two properties, both of which are present in every metal. These are, the metallic lustre, and the power of conducting heat Chemistry, and electricity. Metals exhibit also, in general, a strong attraction for the more negative non-metallic elements, being themselves, as a class, positive. It is particularly towards oxygen, chlorine, bromine, iodine, fluorine, sulphur, and selenium, that metals show this attraction; which, however, varies remarkably in degree, from potassium and its congeners, which can with difficulty be kept in the uncombined metallic state, on the one hand, to the noble metals on the other, which frequently cannot be made directly to combine with oxygen.
Before briefly describing the more important metals, for the majority of them need only be enumerated, we shall prefix some general remarks on the physical and chemical properties of the metals, which may thus be conveniently compressed into a very small space. The most important physical properties of metals are their density, fusibility, volatility, malleability, ductility, tenacity, hardness, and colour.
Metals vary much in density; while potassium and sodium are lighter than water, and lithium and calcium not much heavier, many common metals are very heavy; as iron 7 times, silver 10, lead 11, mercury 13, gold 19, platinum 21, and iridium as much as 26 times heavier than water.
Their fusibility is equally various, for mercury melts at 71° below the freezing point of water, potassium somewhere about + 100°, tin at 440°, lead below a red heat, copper and silver at a full red heat, gold and iron at a white heat, platinum requires a heat stronger than that of any furnace, and iridium has not yet been melted.
So also with regard to volatility, mercury boils at about 600°, potassium and sodium at a red heat, arsenic and tellurium even lower, zinc and cadmium at a strong red heat, antimony perhaps at a white heat, while the remaining metals have not yet been seen in the form of vapour or gas.
Of all metals, gold is the most malleable, and may be beaten into leaves of astonishing thinness; platinum and silver come next, then palladium, copper, nickel, tin, lead, cadmium, zinc, and iron. Most of the others are brittle, or have not been tried, from the difficulty of obtaining them.
Ductility is not proportional to malleability. The most ductile metal is platinum, which yields wire so fine as to be almost invisible to the naked eye; then come gold, silver, iron, copper, tin, zinc, cadmium, and lead. The difference between malleability and ductility is strongly seen in iron, which yields very fine wire, but cannot be beaten into thin leaves.
The tenacity of metals is measured by the weight required to break a rod of equal thickness and length of different metals. Iron is the most tenacious, a fine iron wire requiring a comparatively heavy weight to break it. The other ductile metals are all more or less tenacious.
Of the common metals, gold, platinum, and lead are the softest; tin, zinc, cadmium, and silver somewhat harder; copper and iron the hardest. But the hardest of all metals is iridium, which is so very hard that it cannot be wrought by any tools.
The colour of metals is usually either white, with a tinge of some other colour in many cases, or gray. One metal, gold, is yellow, and one, copper, is red. Titanium was supposed to be of the colour of copper, but the cubic crystals formerly supposed to be titanium are now known to contain other elements, cyanogen and nitrogen, in addition to the metal. Silver is pure white; tin and sodium are yellowish-white; zinc and potassium bluish-white; bismuth reddish-white; antimony, arsenic, and iron, grey. Metals often have a different colour in the compact state and in that of powder. Gold in powder is either brown or nearly black, according to the fineness of the powder. Platinum, grey in the compact and even in the spongy state, is jet black in powder.
The chemical characters of metals are determined by their attractions for oxygen, chlorine and its congeners, and Chemistry. Sulphur. A few general remarks on the relations of these substances to metals will greatly facilitate the subsequent description of the individual metals.
The attraction of metals for oxygen, as has been already stated, varies exceedingly. Some, such as potassium and sodium, rapidly attract oxygen from the air, and are thus oxidized. Others, such as iron and copper, attract oxygen very slowly at ordinary temperatures, and only when moist, but are readily oxidized at a red heat, as is seen on the anvil of the blacksmith, where the scales which form on red-hot iron are an oxide of that metal. Others again, as silver, gold, and platinum, not only do not attract oxygen, even at a red heat, but if already combined with it, lose it when heated to redness. Mercury at a certain temperature is oxidized, but the oxide is decomposed at a temperature very little higher.
Some metals decompose water, seizing its oxygen and liberating its hydrogen, at ordinary temperatures, as potassium and sodium. Others only do so at a red heat, as iron and zinc.
There are various methods of oxidizing metals indirectly. Nitric acid oxidizes and dissolves many metals, indeed most of them. It is particularly used for oxidizing copper, mercury, silver, and antimony. Many metals, such as zinc and iron, are oxidized by dissolving them in hydrochloric or sulphuric acid, and then adding an alkali. On the common view, metals when dissolved in sulphuric acid, are first oxidized at the expense of water, and the alkali only separates the ready formed oxide by taking the acid from it. But this cannot apply to the solution of metals in hydrochloric acid, which forms chlorides; and yet alkalies added to chlorides precipitate oxides, just as with the sulphates. This is an additional argument in favour of the opinion that sulphuric acid is a compound of hydrogen, and that in its salts this hydrogen is replaced by metals.
The action of an alkali, potash, on the chloride of a metal, zinc, is as follows, KO + ZnCl = KCl + ZnO, and its action on sulphate of zinc on the modern view, takes the same form, KO + ZnSO₄ = K₂SO₄ + ZnO. We have already explained the action of metals on hydrochloric and sulphuric acids, and shown that the same view may be taken of both, the phenomena being precisely the same, namely, that the metal is dissolved and hydrogen liberated.
A few metals which cannot be dissolved either by hydrochloric, sulphuric, or nitric acids, are dissolved and converted into chlorides by a mixture of nitric and hydrochloric acids, which is called nitro-hydrochloric acid, or aqua regia. It yields abundance of chlorine, which being in the nascent state combines with the metal. The action of the two acids is as follows; HCl + NO₃ = HO + Cl + 2 HO. According to some, the nitrous acid and chlorine combine to form a new acid, chloronitric acid, NO₄ Cl, and this is the true solvent. At all events, the result is a chloride of the metal, from which, by means of an alkali, the oxide may be formed.
Metals, having so strong an attraction for oxygen, are usually found combined with it, and the oxides of metals are the most important of their compounds. Protoxides, or oxides of the formula MO, are bases, generally powerful ones; sesquioxides M₂O₃ are weaker bases; deutoxides MO₂ are neutral, or even weak acids; teroxides, MO₃ are generally strong acids; as are also oxides of the formula MO₂ and MO₃. The character, therefore, of the oxide depends on the amount of oxygen in it.
The deoxidation of metallic oxides, or their reduction to the metallic state is an operation of great practical importance, most metals being obtained by this means from their ores. The methods of reduction are various.
Some oxides are reduced by heat alone, as those of silver, gold, platinum, mercury.
Most oxides may be reduced by the combined action of heat and hydrogen, or heat and carbon; the oxygen being carried off as water in the first case, and as carbonic acid gas in the second. Hydrogen is much employed in analytical reductions on the small scale, but carbon is alone used in smelting. The reduced metal is melted by the heat, and falls to the bottom of the crucible or furnace. To prevent it from being again oxidized, a flux is employed, that is, a fusible earthy or saline mixture, which covers the surface of the metal with a fluid mass, and protects it from the air.
Many oxides may be reduced from their solutions by means of other metals having a stronger attraction for oxygen. Thus, salts of silver are reduced by mercury, those of mercury by copper, lead, or tin; copper is reduced by zinc or iron, lead by zinc, tin by zinc. This method is often used in the laboratory. Silver, lead, and tin crystallize beautifully when thus reduced.
Many metallic oxides are also reduced by various deoxidizing agents, both from their solutions, and in the dry way with the aid of heat. Protosulphate of iron reduces gold from its solutions, as do oxalic and formic acids. Silver is reduced by formic acid, by aldehyde, and by oil of cloves. Cyanide of potassium, which combines the deoxidizing agency of carbon with that of potassium, is a most powerful reducing agent at a red heat.
Lastly, several metals are reduced, and that in a compact metallic-looking mass, although from solutions at the ordinary temperature, by the galvanic current. This constitutes the electrolyte, which is chiefly applied to copper, silver, and gold. The metals thus obtained are as dense, as hard, and as malleable, as if they had been melted, rolled, and hammered.
Metals are made to combine with chlorine in various ways. Most of them if in a state of fine division combine directly with chlorine gas, generally taking fire in it. But this method is not convenient.
The chlorides of metals may be obtained by acting on the metals or on their oxides with hydrochloric acid, as already explained. As all chlorides, except two, chloride of silver and protocloride of mercury, are soluble in water, this method is much used. The insoluble chlorides are obtained by adding hydrochloric acid or a soluble chloride to any solution of the metal. Thus, hydrochloric acid or chloride of sodium, added to nitrate of silver, precipitate the chloride of silver, HCl + AgO, NO₃ = HO, NO₃ + AgCl, or NaCl + AgO, NO₃ = NaO, NO₃ + AgCl.
The volatile chlorides of some metals, such as aluminum, titanium, &c., which decompose water, are obtained by mixing the oxide of the metal with charcoal heated red-hot, and passing chlorine over the mixture. Aided by the attraction of chlorine for the metal, the carbon deoxidizes the oxide, which otherwise it could not do, and the chloride is deposited in the cold part of the apparatus.
When a chloride is to be reduced to the metallic state, hydrogen, aided by heat, may be used on the small scale, but carbon is of no avail.
Chlorides may also be reduced by other metals, and by various mixtures; also by the galvanic current. Chloride of silver is reduced by the action of iron or zinc; by heating to redness with lime, or by boiling with potash and sugar.
All that has been said of the formation and decomposition of chlorides applies also to bromides and iodides, and with the exception that we cannot employ fluorine itself, which is unknown, to fluorides likewise.
With sulphur, most metals combine, when heated along with it. The insoluble sulphurets may also be formed, in solutions of the metal, by the addition of hydrosulphuric acid, or of a soluble sulphuret, which act on the oxides, chlorides, &c., in the same way.
\[ \text{MO} + \text{HS} = \text{HO} + \text{MS} \quad \text{and} \quad \text{MCl} + \text{K} = \text{KCl} + \text{MS}. \]
In some cases the sulphuret of a metal is obtained by Chemistry, deoxidizing the sulphate. Thus, in the case of barium or potassium, the sulphurets of which are soluble, the sulphate of the oxide is heated with charcoal or hydrogen.
\[ \text{BaO}_2 + \text{C} = 2 \text{CO}_2 + \text{BaS} \quad \text{and} \quad \text{KO}_2 + \text{H}_4 = 4 \text{HO} + \text{K}_8. \]
The sulphurets are reduced in various ways. Some are heated with a mixture of charcoal and carbonate of potash (black flux). The potassium takes the sulphur, while the carbon takes the oxygen of the potash, and the metal is reduced. Some are heated in hydrogen gas, when hydrosulphuric acid is given off, and the metal is left. Some sulphurets are reduced by being heated with other metals, as when sulphuret of mercury is reduced by heating it with iron filings. But on the large scale the usual method is to roast the ore (sulphurets being the chief ores of many metals, as lead, antimony, bismuth, copper, &c.), so as to oxidize both metal and sulphur, and dissipate a great part or the whole of the latter as sulphurous acid. The oxidized residue is then heated with charcoal as usual.
Metals also combine together, especially when heat is applied. It is remarkable that two metals heated together generally melt far more easily than they do separately. This is because the compound metal is always more fusible than the less fusible element, and often more so than the more fusible of the two. Compounds of two or more metals are called alloys, as brass, composed of copper and zinc; bronze, of copper and tin; pewter, of lead and tin; and fusible metal, of lead, tin, and bismuth. Where mercury is one of the elements, the alloy is called an amalgam.
The physical properties of alloys are those of simple metals, and there is nothing in their appearance to indicate their compound nature. In many cases, the addition of a very small proportion of one metal very greatly modifies certain properties of the other, such as fusibility, hardness, tenacity, and the like. A mere trace of arsenic renders gold brittle, and one part of zinc, tin, antimony, and other metals, added to 100, 200, or even 500 parts of iron, much increases both its fusibility and hardness. The subject of alloys is as yet only imperfectly investigated, and many valuable alloys remain to be discovered. It has been ascertained, however, that, while many metals may be fused together in any proportions, the properties for which alloys are valued are best developed when the metals are in atomic proportions, or multiples and submultiples of these.
In briefly noticing the more important metals, we shall divide them into groups, according to their natural analogies. It will be found that these groups are characterized by marked differences in the attraction for oxygen, and also in the nature of the oxides formed, while, in these and many other points, the metals of each group closely resemble each other.
**GROUP I.**
**Metals of the Alkali Proper.**
This group consists of three metals, potassium, sodium, and lithium, which resemble each other as closely as do chlorine, bromine, and iodine. This resemblance is indeed so close that it is often difficult to distinguish between their compounds. They have all so strong an attraction for oxygen that they cannot be preserved in the metallic state unless they are protected from the contact of air, water, and other oxidized substances. They are all oxidized by exposure to air, and all decompose water at ordinary temperatures. Their protodoxides are the alkalis, potash, soda, and lithia.
14. **Potassium.**
Symbol K (Kaliun). Equivalent = 39.2.
This metal occurs, in the form of salts of its oxide, potash, and in that of its chloride, in the ashes of plants, especially land-plants. Chloride of potassium also occurs in those of Chemistry, sea-plants. Potash also occurs, combined with alumina and silicic acid, in felspar, which, as already mentioned, is one of the most abundant minerals. The metal is best obtained from the carbonate of potash, KO, CO₄, by exposing it to a white heat, mixed with charcoal, in a bottle of malleable iron. The carbon is oxidized at the expense of the potash, forming carbonic oxide gas which escapes, while the metal is volatilized and condensed in a receiver filled with naphtha, a liquid containing no oxygen. The process is not very productive, because the carbonic oxide forms, with part of the metal, a dark gray pulverulent compound, which is carried forward by the current of gas, and is apt to choke up the tube. This compound is dangerous, as it takes fire and explodes in contact with water. The metal is purified by melting it under naphtha, and pressing it through leather. If necessary it may be distilled in a small iron retort, and collected in naphtha.
Potassium has a highly metallic lustre, and a bluish-white colour. It is somewhat lighter than water, its density being 8650. It melts at 150°, and if heated takes fire, burning to oxide or potash, KO. It combines with equal energy with chlorine, bromine, iodine, sulphur, &c. Its attraction for oxygen is such that it decomposes all oxidized substances when heated with them, and many at the ordinary temperature. When thrown on the surface of water, it instantly melts, takes fire, and floats on the water, burning with a pink flame. Here the first effect is to deprive the water of oxygen, liberating hydrogen, which is set fire to by the heat evolved. The flame therefore is that of hydrogen and potassium mixed. But if the metal, inclosed in paper, or held by a pair of forceps, be plunged under the surface, no flame appears. Hydrogen gas is abundantly disengaged, and the metal even becomes red-hot under water. The oxide formed is dissolved. Exposed to air, potassium rapidly tarnishes and attracts, first oxygen, then carbonic acid and water, so that, in a short time, it is transformed into a strong solution of carbonate of potash. When heated with the oxides, chlorides, fluorides, &c., of such bodies as boron, silicon, magnesium, aluminum, &c., it deprives these substances of oxygen, and liberates the boron, silicon, and metals they contain.
Protoxide of potassium, or potash, KO = 47.2. Hydrate of potash or caustic potash, KO.HO = 56.2.
The anhydrous protoxide or dry potash can only be obtained by heating the metal in dry oxygen gas. When it has once been dissolved, or when obtained from a solution, Hydrate of potash is obtained by the action of hydrate of lime on a boiling solution of carbonate of potash, when the lime takes the carbonic acid, forming an insoluble carbonate, and the free potash dissolves. The clear solution, boiled rapidly down in a clean iron or silver vessel, till it flows like oil, forms, on cooling, a hard solid mass of hydrate of potash or caustic potash, KO.HO. This 1 eq. of water cannot be expelled by heat.
Caustic potash is very soluble and deliquescent. It also attracts carbonic acid from the air, and is converted into carbonate, if not kept in tightly-stopped vessels. It is very caustic, and has a burning alkaline taste. It seems to act as a caustic from its attraction for water. It neutralizes all acids, forming salts, which are called the salts of potash. Many of them are useful, as the carbonate, nitrate, sulphate, bitartrate, oxalate, &c. The solutions of potash and of its salts, as well as of all other soluble compounds of potassium, are recognised by giving, with excess of tartaric acid, a crystalline precipitate of the bitartrate, with bichloride of platinum a yellow crystalline precipitate of the double chloride of platinum and potassium, and with perchlorate of potash a crystalline precipitate of the perchlorate.
Caustic potash is much used both in surgery and in chemistry. It precipitates the insoluble oxides of most metals. In the arts it is employed in making soap, and in a variety of other ways. The carbonate is used in the manufacture of glass, and the nitrate in that of gunpowder.
Potassium forms, in certain circumstances, not well understood, a peroxide, KO₂, which is a yellow powder of no particular interest.
Chloride of potassium, KCl, is produced when hydrochloric acid acts on potash. HCl + KO.HO = KCl + 2 HO. It crystallizes in cubes, has a bitterish saline taste, and much resembles chloride of sodium or sea-salt. This salt is found in kelp, the ashes of sea-weed, and is used in making alum.
Iodide of potassium, KI, is formed along with iodate of potash, KO.IO₃, when iodine is dissolved in solution of potash. I₂ + 6 KO = 5 KI + KO.IO₃. The mixture, when heated to redness, gives off the oxygen of the iodate, and leaves the pure iodide. 5 KI + KO.HO = 6 KI + O₂. This salt is much used in medicine and also as a reagent in chemistry. It crystallizes in cubes like the chloride, and is soluble in alcohol.
The bromide and fluoride are very like the chloride and iodide, crystallizing also in cubes.
The sulphuret of potassium, KS, is formed by heating the elements together, or by heating sulphate of potash in a current of hydrogen gas. KO.SO₄ + H₂ = 4 HO + KS. It is a white or yellowish powder, soluble in water. There are other sulphurites with more sulphur, especially the pentasulphuret, KS₅, which forms a solution of a deep yellow colour.
15. Sodium.
Symbol Na (Natrium). Equivalent = 23.
This metal is found, oxidized, as carbonate, in the ashes of sea-plants, or kelp, barilla, and varve. But it occurs chiefly as chloride of sodium constituting sea-salt and rock-salt, which are most abundant mineral compounds. Chloride of sodium is also present in small proportion in all waters, even in rain-water, and in large amount in salt springs, which are very common in many districts. It is probably also present in all soils, and in most rocks, and is a constant ingredient of the ashes of plants.
Sodium is obtained from the carbonate exactly as potassium is; only, as the metal forms no combination with carbonic oxide, the process is more productive. Like potassium, it must be collected and preserved under naphtha. Chemistry. It has a yellowish-white colour and bright lustre, is rather heavier than potassium, its specific gravity being 9700, and also less fusible and less volatile. It decomposes water, but does not burn on its surface, although if a few drops of water be sprinkled on a bit of sodium, the hydrogen will then take fire and set fire also to the metal, giving an intensely yellow flame. In all other respects sodium resembles potassium; but this character of giving a strong and pure yellow colour to flame is found in all the salts of sodium, and at once distinguishes them from those of potassium, which colour flame of a faint lilac, not easily observed, since the presence of a trace of sodium or of many other metals overpowers it. Potassium itself burns with a lively pink flame, but in its salts the effect is much less marked, whereas in those of sodium the effect on flame is as strong as in the metal itself.
Protoside of sodium or soda, like potash, is best known in the form of the hydrate, or caustic soda, NaO.HO, which is entirely similar to caustic potash, and is prepared from the carbonate exactly in the same way. Hydrate of soda, like that of potash, is deliquescent, and also attracts carbonic acid from the air, but the carbonate of soda differs from that of potash, which is anhydrous and very deliquescent, and can hardly be made to crystallize, whereas carbonate of soda forms very large crystals, containing at least half their weight of water of crystallization and efflorescence, that is, losing water and becoming opaque and powdery in the air.
Soda is best distinguished from potash by its action on flame, and by the characters of its salts. We have seen that potash forms nearly insoluble salts with perchloric acid, bichloride of platinum, and excess of tartaric acid, to which may be added carbazotic or nitropreric acid. With all of these, and indeed with acids in general, soda forms soluble salts. There are only two salts of soda insoluble, or nearly so, namely, the silicofluoride of sodium, formed by hydrofluoric acid, when added to soda or its salts, and the antimoniate of soda. But potash also forms an insoluble silico-fluoride; and hence the only test which can be used to distinguish soda from potash by forming a precipitate is antimoniate of potash, which of course does not act on the salts of potash. Unfortunately the solution of this test does not keep well; so that chemists generally make use of the action of sodium and its salts on the flame of alcohol, or convert the soda into certain salts which differ from the corresponding salts of potash, as has been mentioned in regard to the carbonate. The sulphate of soda is also efflorescent, and crystallizes in four-sided prisms, while that of potash is anhydrous, and forms six-sided prisms and pyramids. The nitrate of soda forms rhombic crystals, while that of potash yields six-sided prisms.
Soda is used for much the same purposes as potash; and as pure carbonate of soda is now made at a cheap rate from sea-salt, while the commercial carbonate of potash is not only dearer, but very impure, soda is generally preferred. Its chief uses are in making soap (the soaps of soda being hard, while those of potash are soft), and glass. It is also used in bleaching and calico-printing, the cloth being boiled with soda in various processes.
There is a peroxide of sodium, which seems to be a deuteroxide, NaO₂, but is little known.
Chloride of sodium, NaCl, sea-salt or rock-salt, is the most important compound of sodium. It is the type of all neutral salts, which indeed, as a class, are named from it. It has a purely saline taste, and strong antiseptic properties, fitting it for use as a condiment to food (for which purpose it is indispensable, since blood cannot be formed without salts of sodium), and for preserving meat. Chloride of potassium cannot be used for either of these purposes.
Sea-salt crystallizes in cubes, which are generally hollow. Chemistry. Rock-salt is often found in large transparent masses, which cleave readily in the boundary planes of the cube, and may thus be shaped into perfect cubic crystals. It is almost equally soluble in hot and in cold water.
In the arts, salt is used for the production of chlorine, chloride of lime or bleaching powder, and hydrochloric acid. It is also used as a manure.
The bromide, iodide, fluoride, and sulphuret of sodium, are quite analogous to those of potassium.
16. Lithium.
Symbol Li. Equivalent = 6.5.
This metal, the third of the alkaline group, is rare, occurring only in small proportion, seldom more than 3 or 4 per cent. in a few rare minerals, such as spodumene, petalite, lithion-mica, and lepidolite. The metal is little known, but is analogous to sodium and potassium, being heavier than either, and having apparently stronger affinities.
The hydrated oxide of lithium, LO, HO, analogous to caustic potash and soda, is less soluble and less caustic, but like them attracts moisture and carbonic acid from the air. The carbonate is sparingly soluble. The sulphate, nitrate, and chloride are similar to those of potassium, except that the two last-named salts are deliquescent. Lithium and all its salts are easily recognised before the blow-pipe by the property of giving to flame a blood-red colour. It differs from potassium and sodium also in forming a sparingly soluble carbonate, and a nearly insoluble phosphate.
Lithia has not been applied to any useful purpose, being too rare. It occurs in small proportion in various waters, and possibly contributes to their action on the system. It is worth while to mention that the minerals which contain lithia, especially lithion-mica, and lepidolite, which is a kind of mica, have been found hitherto always associated with certain minerals, namely, topaz, albite, or soda-felspar, and tin ore. The occurrence, therefore, of lithia, especially along with topaz and albite, may be regarded as an indication that tin ore is not distant. The above-named minerals are found together in all the tin districts of Europe, in Cornwall, Saxony, and Sweden, and we have seen the same combination in two districts, one in Scotland, the other in Ireland; in both of which tin ore was also found, but as yet not in available quantity.
The group just described is very remarkable from the great analogy which pervades it, and from its complete parallelism with the group of chlorine, bromine, and iodine. In both, the gradation of properties is perfect, and the atomic weight of the middle elements, sodium and bromine, is, in both cases, the mean between those of the extremes. The most probable explanation of these relations is, that all these bodies are really compound, and contain in each group some common element, the variation in the amount of which causes the change of properties. In other words, these would be regarded as groups of homologous compounds, and they closely resemble such groups. But in the meantime, as we cannot prove them to be compounds, they remain elements to us.
GROUP II.
Metals of the Alkaline Earths.
The next group contains four metals, those of the alkaline earths, in which the gradation of properties seen in the first group is repeated or rather continued. In this group the protoxides are more and more sparingly soluble till the last, which is insoluble; the carbonates are insoluble in water, and the sulphates, with one exception, are either sparingly soluble or insoluble. By these characters they are readily distinguished from the metals of the first group.
17. Barium.
Symbol Ba. Equivalent = 89.5.
This metal, which is little known, has been obtained hitherto only by means of a powerful galvanic battery. It is much heavier than the preceding metals, its density being above that of oil of vitriol.
The protoxide of barium or baryta is found in nature, combined with carbonic acid and sulphuric acid, forming the minerals witherite and heavy spar. It occurs also in a few other minerals, chiefly silicates. To obtain the pure anhydrous oxide, BaO, the carbonate is heated to whiteness, mixed with a little charcoal. By this means the carbonic acid is partly expelled as such, partly as carbonic oxide, and baryta is left. Or the nitrate of baryta is cautiously heated in an earthen crucible, when it melts, and gives off nitrous acid and oxygen, baryta being left. It forms a gray porous earthy mass, which, like quicklime, produces intense heat when brought in contact with water, with which it forms a fine white powder, hydrate of baryta, BaO, HO. This is dissolved in considerable quantity by hot water, and the hot saturated solution deposits, on cooling, fine tabular crystals of another hydrate, BaO, 10 HO. The hydrate is much less soluble in cold water than in hot, but still the solution has a strong styptic, almost caustic, alkaline taste, and attracts carbonic acid from the atmosphere, forming the insoluble carbonate. The nitrate of baryta, chloride of barium, and other salts of this base, are easily obtained from the carbonate by the action of the proper acids. But as the carbonate is much more rare than the sulphate, and as the sulphate is quite insoluble in water and acids, it must be decomposed, so as to allow of its being converted into other salts. This is effected by mixing it in fine powder with ½th of its weight of charcoal, and heating the mixture to a strong red heat for two hours in a covered crucible, leaving a small aperture for the escape of gas. The action is as follows: BaO, SO₄ + C₁ = 4 CO + BaS. The products are carbonic oxide gas and sulphuret of barium. The latter compound is dissolved by boiling water, which leaves any impurities as well as any excess of charcoal undissolved. The solution, treated with nitric acid, yields the nitrate; with hydrochloric acid, the chloride; with carbonate of potash, soda, or ammonia, the carbonate; and if boiled with oxide of copper, it yields the hydrate of baryta. The formation of the nitrate is as follows: BaS + HO, NO₃ = HS + BaO, NO₃. That of the chloride is BaS + HCl = HS + BaCl. That of the carbonate is BaS + KO₂, CO₂ = KS + BaO, CO₂, and that of the oxide is BaS + CuO = CuS + BaO. The oxide thus formed instantly combines with water to form the crystallized hydrate.
Baryta is characterized by the extreme insolubility of its sulphate in water and acids, and its salts are used as tests for sulphuric acid; which again is used as a test for baryta. Hydrofluosilicic acid produces, in the salts of baryta, an insoluble crystalline precipitate. Baryta differs also from the three preceding metals in forming an insoluble carbonate, and in its own sparing solubility.
Chloride of barium, prepared as above stated, crystallizes in tabular crystals, BaCl₂ HO. It is much used as a test for sulphuric acid, and as a means of determining the quantity of that acid in analysis. It is also used in medicine.
The sulphuret of barium, BaS, is soluble in water, as has just been mentioned. It is much used as a means of obtaining the other salts of baryta from the insoluble sulphate. Baryta, and all its salts, except the sulphate, which, being insoluble in all menstrua, is inert, are very poisonous.
18. Strontium.
Symbol Sr. Equivalent = 43.8.
This metal is hardly known, but is very analogous to barium. The protoxide, strontia, is found as carbonate or Chemistry, strontianite, and sulphate or celestine. The anhydrous oxide, SrO; the hydrates, SrO, HO, and SrO, 10 HO; the carbonates, SrO, CO₂; the nitrate, SrO, NO₃; the chloride, SrCl; the sulphate, SrO, SO₄, and the sulphuret, SrS, are all prepared precisely as in the case of barium, and are similar to the corresponding compounds of that metal as the salts of sodium are to those of potassium. The chief differences are, that the sulphate is not absolutely insoluble, and the hydrate rather less soluble than the corresponding compounds of baryta. The chloride is deliquescent, and strontia and all its salts give to flame a fine crimson colour. The nitrate is used, indeed, in making red fire for signals and for the theatres. There is no other useful application of strontia or its salts.
19. Calcium.
Symbol Ca. Equivalent = 20.
This metal also is little known. But the protoxide, CaO, is the important substance quicklime. It is found like baryta and strontia, as carbonate in marble, limestone, chalk, and calcareous spar, and as sulphate in gypsum, alabaster, and selenite. The shells of shell-fish consist chiefly of carbonate of lime, and the rocks above mentioned have been in many cases derived from the accumulation of shells and their debris, as is proved by the frequent occurrence of chalk, limestone, and marble, entirely composed of shells.
Pure lime, CaO, is obtained by heating pure marble, &c., to redness in a current of air, when the carbonic acid is expelled and quicklime is left. Quicklime is still more sparingly soluble than strontia. It combines with water with great energy, giving out much heat, and producing hydrate of lime or slaked lime, CaO, HO. Hydrate of lime is very sparingly dissolved by water, forming a solution called lime-water, which has an alkaline styrpical taste, neutralizes acids, and attracts carbonic acid from the air, forming the insoluble carbonate. Lime-water is a much weaker solution than strontia-water, and strontia-water than baryta-water, so that there is a regular gradation of solubility in the group.
Lime is much employed for making mortar and in agriculture. The uses of marble and limestone for building, and of chalk for various purposes in medicine, and for the preparation of effervescing drinks, are well known. The presence of lime in any solution is detected by adding first ammonia to neutralize any acid, and then oxalate of ammonia, which produces a precipitate of the insoluble oxalate of lime. Lime and its salts are also used to detect oxalic acid.
Chloride of calcium, CaCl, is formed when hydrochloric acid acts on carbonate of lime. It is very soluble, crystallizes with difficulty, and is very deliquescent. It is much used by chemists from its strong attraction for water, to deprive other substances, such as gases, ethers, and the like, of moisture; also to collect water in analysis, so that its weight may be ascertained.
20. Magnesium.
Symbol Mg. Equivalent = 12-2.
This metal is obtained by the action of potassium on the chloride, MgCl + K = KCl + Mg. It is silvery white, of a brilliant lustre, and malleable. It may be kept in dry air or under water. When heated in oxygen it burns with much light, producing the protoxide or magnesia, MgO.
This oxide magnesia, MgO, is best obtained, like lime, by heating the carbonate. Hence it was called calcined magnesia, the carbonate being then called magnesia. Magnesia is insoluble in water, but has an earthy taste. It is quite white, while the three preceding alkaline earths are more or less gray. Hydrate of magnesia, MgO, HO, is formed by precipitating the soluble salts of magnesia by caustic potash, soda, or ammonia. It is white, and resembles the anhydrous oxide, into which it is converted by Chemistry, a low red heat, water being expelled.
Magnesia is a strong base, and neutralizes all acids. It is distinguished from the three preceding oxides by its insolubility and by forming a soluble sulphate. It agrees with them in forming an insoluble carbonate. It is found in nature as carbonate in some localities, but chiefly in the form of the double carbonate of lime and magnesia, dolomite, or magnesian limestone. The sulphate occurs in some springs, as in Epsom and Cheltenham waters. Hence its name of Epsom salt.
Magnesia and its carbonate are much used in medicine as antacids. The sulphate is an excellent laxative.
Magnesia has a remarkable tendency to form double salts, as carbonate of lime and magnesia; sulphate of magnesia and potash (ammonia and soda may be substituted for the potash); and phosphate of ammonia and magnesia. The latter being quite insoluble, especially where an excess of ammonia is present, magnesia is detected by converting it into this double phosphate, which is done by adding first carbonate of ammonia and then phosphate of soda.
The chloride of magnesium, MgCl, is obtained by dissolving magnesia in hydrochloric acid, evaporating to dryness, and igniting after the addition of sal-ammoniac, the vapours of which protect the chloride from the action of the air, which would otherwise oxidize the metal, expelling the chlorine. The fused mass of chloride must be kept in well-stopped vessels, as it is very deliquescent. It is from this salt that magnesium is obtained, and we mention it here because, as the metal is not rapidly oxidized in the air like those which precede, and appears to be malleable, it is possible that it may be in time applied to useful purposes.
It will be observed, that while barium, strontium, and calcium form a triad, parallel to that of potassium, sodium, and lithium, and with the same gradation in properties, such as solubility, force of attraction, and atomic weight, magnesium, with some points of analogy to these, yet in other points stands by itself. It is the first metal which, although having a strong attraction for oxygen, can yet be kept unchanged in air and water, the first also whose oxide (a protoxide) is insoluble in water. But it is placed with the three preceding metals, because it differs still more from those which follow. Strictly speaking, it does not belong to the same group with the three which precede it, and which form so well-marked a triad; and we shall see that its analogies are rather with zinc, a metal belonging to a different part of the series. It is, in fact, isomorphous with zinc.
GROUP III.
Metals of the Earths Proper.
The next group is that of the metals of the earths proper, which are five in number. Only one of these, however, is of much importance, the others being rare, and two of them exceedingly so. They form sesquioxides, which are bases, but not powerful, being expelled from their combinations by protoxides in general. These oxides are insoluble in water, and have an earthy aspect. The metals are little known, but aluminium is said to have been recently obtained on a larger scale than formerly, and to admit of useful applications.
21. Aluminum.
Symbol Al. Equivalent = 13-7.
This metal is obtained from the chloride by the action of potassium, and has hitherto been described as a dark-gray nearly black powder, infusible, but taking metallic lustre under the burnisher. Recently it is said to have been deposited on the surface of other metals, by means of the galvanic current, as copper is in the electrolyte, in a perfectly compact metallic state, with a bright silvery lustre and co- lour, and permanent in the air. When heated in oxygen, it burns with a brilliant light to sesquioxide. It is this sesquioxide which is so important from its abundance in nature.
**Sesquioxide of Aluminum—Alumina**, \( \text{Al}_2\text{O}_3 = 51.4 \).
This earth is, next to silica, the most abundant solid constituent of the earth's crust. It forms a large proportion of all felspar, and felspar is a constituent of most rocks. In decayed or disintegrated felspar, which constitutes clay, alumina preponderates; and in some clays, such as pipe-clay and porcelain clay, it is nearly pure. Alumina also occurs crystallized in the sapphire and ruby, which contain only a mere trace of colouring matter, and in corundum.
Pure alumina is obtained from alum, which is a double sulphate of alumina and potash, by adding carbonate of potash, which produces a bulky gelatinous precipitate of hydrate of alumina. This is well washed with hot water. Since alumina does not combine with carbonic acid, the carbonic acid of the carbonates escapes as gas. The washed hydrate is not yet pure, retaining some potash. It is dissolved in hydrochloric acid, and reprecipitated by ammonia, again washed, dried, and ignited, when the bulky hydrate, becoming anhydrous, shrinks to a small bulk. Another method, which does not require the long and tedious washing of the hydrate, is to precipitate alum by chloride of barium, which throws down the sulphuric acid as sulphate of baryta, while chloride of potassium and hydrochlorate of alumina remain dissolved. The solution is dried up and the residue ignited, when the hydrochloric acid is expelled, and there is left a mixture of anhydrous alumina and chloride of potassium. The chloride is removed by hot water, and the alumina, which in this state is easily washed, is then dried and ignited, when it appears as a dense earthy white powder. That obtained by igniting the hydrate is translucent, and forms hard lumps.
Alumina is insoluble in water, but forms with it a plastic mass, which can be moulded into any shape, and when ignited retains the form given to it, and becomes hard, and much contracted in volume from the loss of water. When freshly precipitated the hydrate is very soluble in acids, but after ignition it dissolves in them very slowly. Its solutions have a sweetish astringent taste, and are styptic. Alumina is recognised by its being precipitated by caustic and carbonated potash, soda, and ammonia; and by its redissolving easily in an excess of caustic potash or soda, but not in ammonia. It may also be recognised by forming, with sulphuric acid and potash, a solution which, on evaporation, readily yields octahedral crystals of alum.
Alumina is useful as the chief constituent of all plastic clays, such as pipe-clay, porcelain-clay, brick-clay, and fire-clay. In these it is combined with a little silica. In the form of alum and acetate of alumina, it is much employed in dyeing and calico-printing. Alum is also used in medicine.
Alumina is the first sesquioxide we have come to, and is the type of such oxides.
Chloride of aluminum is a volatile fuming liquid, formed when chlorine gas is passed through a red-hot tube containing alumina intimately mixed with charcoal. The charcoal, aided by heat alone, cannot deoxidize alumina; but when the attraction of chlorine for the metal is added, the carbon is oxidized, and passes off as carbonic acid or carbonic oxide.
\[ \text{Al}_2\text{O}_3 + \text{C} + \text{Cl}_2 = 3\text{CO} + \text{AlCl}_3. \]
The chloride is a sesquichloride. It must be carefully kept out of contact with water, which it instantly decomposes, forming hydrochlorate of alumina:
\[ \text{AlCl}_3 + 3\text{HO} = (\text{Al}_2\text{O}_3 + 3\text{HCl}). \]
This action on water is the reason why the chloride fumes in the air. Potassium decomposes it, setting free the metal as a dark-gray powder.
The other metals of this group are—22. Glucinium, \( G = 26.5 \), which is found as sesquioxide in the beryl and the emerald, and is named from the sweet taste of its salts. The oxide glucina, \( G_2O_3 \), resembles alumina, but it differs from Chemistry, it in being soluble in carbonate of ammonia. 23. Yttrium, \( Y = 32.2 \), the sesquioxide of which, or yttria, is found in two or three very rare minerals, such as gadolinite, and yttriotantalite, which occur at Ytterby, in Sweden; hence the name. Its salts are also sweetish, but it is of little importance. 24. Thorium, \( Th = 59.6 \), found only in one very rare mineral, thorite, and hitherto only seen by one or two chemists; and 25. Zirconium, \( Zr = 22.4 \), the sesquioxide of which, zirconia, is found in the zircon or hyacinth. It also is somewhat analogous to alumina, but is not of sufficient importance to justify us in dwelling on it more fully.
Zirconium, in some of its properties, connects this group with the next.
**GROUP IV.**
This group consists of metals, the oxides of which are so little known, that we cannot say with certainty that any one of them is known in a perfectly pure state. The oxides of these metals, in fact, occur generally together, and being very similar to one another, their separation is a matter of very great difficulty. We shall therefore only mention their names, for their atomic weights are for the most part still doubtful. They are, 26. Cerium; 27. Lanthanum; 28. Didymium; 29. Erbium; and 30. Terbium. It is in this group that the oxides begin to be coloured. Peroxide of cerium is brown, and the salts of several of them have some degree of colour. It is now believed that the colour observed in some of the salts of yttria really depends on the presence of one or more of these metals. Zirconium has also a certain degree of analogy to tin.
**GROUP V.**
We shall now proceed to a group of metals of far greater importance, the first of which is iron. The metals of this group are seven in number, namely, iron and manganese, zinc and cadmium, cobalt and nickel, and tin. It will be seen that six of them are enumerated in pairs, and in fact the two metals of each pair have not only a striking analogy in many points, but also occur associated, one being seldom found without the other. In this group the attraction for oxygen is still very powerful, but the metals do not decompose water rapidly at ordinary temperatures, although they do so at a red heat. Their protoxides are powerful bases, and their sesquioxides, where they exist, are weak bases. When they form teroxides, these are strong acids. The compounds of most of them are coloured.
31. Iron.
Symbol Fe (Ferrum). Equivalent = 28.
This, the most valuable of all metals, is the first we have come to that is found uncombined, or in the metallic state; it occurs in that state in meteoric iron, and perhaps also in masses of terrestrial origin. There are, in different parts of the world, as in Siberia, in South America, and on the west coast of Africa, large masses of iron, declared by the native tradition to have fallen from heaven. That on the coast of Africa is almost a hill in size, the others are smaller, but yet of many tons weight, and many still smaller masses of the same kind exist. There is one of several tons weight in the court of the Government Building at Aix la Chapelle, which was found just below the surface of one of the streets, and of the fall of which no record is left. It probably fell before the city was founded. All the known masses of meteoric iron agree in character, being very hard, but malleable, and containing small quantities of nickel, cobalt, chromium, arsenic, and sulphur, with frequently a little silica. Such masses have been often seen to fall, and have been picked up while yet hot. When they fall at night, they are seen as luminous meteors, which finally explode and burst into fragments, and these, if large, bury themselves in the ground by the force of their fall. This Chemistry, form of iron, however, is rare, although very interesting, from its peculiar composition, always containing the same impurities, and from the uncertainty of its origin. At one time these meteorites were supposed to come from the moon; but the prevalent opinion now is, that they are portions of planetary matter, either undergoing condensation, or else the fragments of some heavenly body that has burst or exploded, and continuing to revolve round the sun. They frequently enter our atmosphere, when they cross the earth's orbit, and then appear to take fire in it, and be attracted to the surface. Multitudes of them pass through without falling, their centrifugal force being sufficient to resist the gravitation of the earth.
Iron is usually found oxidized; either as sesquioxide $Fe_2O_3$, called red hematite, or black hematite, a hydrate of the same oxide; or carbonate of protoxide, $FeO.CO_2$, which is called clay iron ore; or magnetic oxide, or black oxide of iron, or loadstone, of which there are two kinds, $Fe_2O_3$ and $Fe_4O_5$. It also occurs as bisulphuret of iron, $FeS_2$, called iron pyrites, and another sulphuret, called magnetic pyrites. The metal is obtained chiefly from hematite, magnetic oxide, and carbonate. These ores are heated with charcoal or coke, and a flux composed of sand and limestone. The reduced metal combines with a small quantity of carbon, forming a fusible compound, pig or cast-iron. This is subsequently melted in a puddling furnace, and exposed to a current of air, to burn off the carbon. As it becomes purer, it becomes also less fusible, till at last a white heat the purified metal is only a pasty, not a fluid state. At this stage it is hammered and rolled to expel the last traces of carbon, and then constitutes pure or malleable iron, such as is used for horse-shoes, horse-shoe nails, gun-barrels, and rails, as well as wire; for it is only when pure that it can be drawn out into fine wire.
Iron has a specific gravity of about 7800 (water = 1000). It is rather soft, especially when hot, and malleable. It is visible only in the most intense heat of a white furnace. Heated in a current of air, or in oxygen, to whiteness, it burns and is rapidly oxidized. At a red heat it is still oxidized on the surface; and the oxide, which is black or magnetic oxide, scales off under the hammer, and is called smithy ashes. At ordinary temperatures, if exposed to air and moisture, it is slowly oxidized, forming the brown sesquioxide, and is said to rust.
The uses of iron, in the pure metallic state, are too well known to require enumeration. The chief objection to it is that it cannot be cast nor even hammered at ordinary temperatures, so that it must be heated red-hot in order to be manufactured. Its value depends on its tenacity, a property in which it surpasses all other metals.
Iron and Oxygen.
Iron forms several oxides. Three appear to be direct compounds of iron and oxygen, and two to be composed of the others united together.
1. Protioxide of iron, $FeO$, is obtained by heating the carbonate or sesquioxide to a low red heat in hydrogen gas. If heated too strongly, it is reduced to the metallic state. When pure, it is of a grass-green colour, but it is apt to absorb oxygen from the air and to become sesquioxide, so that it is little known. It is a powerful base, and its salts are either bluish-green or colourless, the latter in a few cases only. These salts have an inky taste, and give a deep blue precipitate of Prussian blue with the ferricyanide or red prussiate of potassium. Caustic alkalies precipitate a white hydrate, which instantly attracts oxygen, and passes through green to the brown sesquioxide. Carbonated alkalies give a white bulky carbonate, which also becomes green, and finally brown, being converted into sesquioxide, and losing its carbonic acid. Hydrosulphuric acid or sulphuretted hydrogen does not precipitate these salts; sulphuret of ammonium causes a black precipitate of sulphuret of iron. Infusion of galls and meconic and sulphocyanic acids have no action on pure solutions of the protoxide. That oxide and its salts are characterized by their strong tendency to pass into sesquioxide, by absorbing oxygen; and they deoxidize many substances in consequence. The carbonate occurs in many mineral springs, dissolved by excess of carbonic acid.
2. The sesquioxide or peroxide of iron $Fe_2O_3$, is far more permanent, not having any tendency to absorb oxygen under ordinary circumstances. It is found pure in red hematite, hydrated in black hematite. To prepare it, the sulphate of the protoxide, or green vitriol, is boiled with nitric acid, some sulphuric acid being added, when it becomes sulphate of the peroxide or persulphite. The addition of an alkali throws down a bulky brown hydrate of the sesquioxide, which, being washed, dried, and ignited, leaves the sesquioxide. It is a weak base, and is expelled from its salts by all protoxides, even by protoxide of iron. Its formation from the protosulphate or green vitriol is as follows:
$$2(FeO.SO_4) + NO_2 + SO_2 = NO_3 + Fe_2O_3 + 3SO_3.$$
Like alumina and other sesquioxides, it requires 3 eqs. of acid to form a neutral salt. On account of the permanence of this oxide, when we wish to test for iron, it is first converted into sesquioxide by boiling with nitric acid. Its characters are well marked. Alkalies, caustic and carbonated, throw down a brown precipitate of sesquioxide, which does not combine with carbonic acid. Ferrocyanide of potassium, or yellow prussiate, produces the deep blue precipitate of Prussian blue; the red prussiate only changes the colour of the solution to a dirty green. Infusion of galls produces ink, and sulphocyanic and meconic acids produce a deep blood-red colour. The salts of sesquioxide of iron are generally brown, and have a strong inky taste.
Both oxides and their salts are used in medicine, as tonics and astringents. The salts of the peroxide are much employed in dyeing and calico-printing, as they strike either black or various shades of purple, lilac, and gray, with cochineal, logwood, and other red dyes, with which alumina gives crimson or pink colours.
The blood of animals contains iron in considerable quantity, which is found in the ashes of the blood as sesquioxide. It is present chiefly in the red globules, and indeed in the colouring matter of the globules. But it is not known whether their colour depends on the presence of iron, nor in what form of combination the iron exists. There can be no doubt that it has an important function to perform, probably connected with the absorption of oxygen in respiration; and as iron is thus essential to animal life, so it is found as a never-failing constituent of those plants on which animals feed, and that, in the form of sesquioxide, at least, it takes that form in the ashes.
3. Ferric acid, $Fe_2O_3$, is formed when the sesquioxide is ignited along with potash, or with nitrate of potash. The oxide takes up oxygen, and the acid thus formed combines with the potash, forming a salt which is very soluble in water, to which it gives a deep purple colour. It does not keep, however; for on standing, oxygen is evolved, and sesquioxide is deposited. It may be preserved somewhat longer, and even obtained in dark crystalline grains, if the solution contain a large excess of potash. Ferrate of potash, $KO.FeO_4$, is rapidly deoxidized by contact with organic matter, such as the skin, or paper.
4. Magnetic oxide or black oxide of iron, exists in two forms, both of which may be produced artificially by precipitating a mixture of protoxide and sesquioxide in due proportion. The two magnetic oxides are $Fe_2O_4$ and $Fe_3O_4$. The former may be regarded as formed of 1 eq. of protoxide and 1 eq. sesquioxide, $FeO + Fe_2O_3 = Fe_3O_4$. The latter contains the elements of 2 eqs. protoxide, and 1 eq. sesquioxide, $2FeO + Fe_2O_3 = Fe_3O_4$. The native loadstone Chemistry, or natural magnet, or magnetic iron ore, is a mixture or compound of the two. To prepare the oxide Fe₂O₃ artificially, sulphate of the protoxide is divided into two equal parts, and one of these converted into sulphate of sesquioxide by boiling with nitric acid. The two portions are then mixed, and the addition of an alkali, aided by a boiling heat, throws down a black precipitate, which, when dry, is strongly magnetic, and does not attract oxygen from the air. As the two halves of the sulphate contain equal quantities of iron, the oxide thus prepared must be that which is Fe₂O₃ = 2 FeO + Fe₂O₃. The oxide Fe₂O₃ is prepared exactly in the same way, only two-thirds of the sulphate are converted into sesquioxide, which gives the oxide Fe₂O₃ = FeO + Fe₂O₃. This also is black, permanent, and magnetic.
With chlorine, iron forms two chlorides. The protocloride, FeCl₁, is formed when iron is dissolved in hydrochloric acid. It is soluble, and has the green colour and character of a salt of protoxide. The sesqui chloride, Fe₂Cl₃, is formed when the sesquioxide is dissolved in hydrochloric acid, and evaporated to dryness. It forms an orange yellow mass, which is volatile at a high temperature. It is much used in medicine, in the form of an alcoholic tincture, called tincture of muriate of iron. It occurs among the volatile products of volcanic action.
The protoidide of iron, FeI₁, is formed, when iron and iodine, the former in excess, are placed in contact under water. Heat is developed, and a green solution of the iodide is formed. When boiled down, it leaves a dark green deliquescent mass. The iodide is decomposed by the oxygen of the air, which sets free iodine, and converts the iron into sesquioxide. The iodide is much used in medicine, and is preserved by drying it up with the addition of sugar, which covers the particles, and protects them from the air. Sugar is used in the same way to preserve the precipitated carbonate of protoxide of iron from oxidation.
Sulphur and iron unite in several proportions. The protosulphuret, FeS₁, is formed when iron filings and sulphur are heated together, when much heat and light are developed. It is also formed when a stick of sulphur touches a white-hot rod or bar of iron. The bar is instantly perforated, and the melted sulphuret drops down. It is used in the preparation of hydrosulphuric acid. The bisulphuret FeS₂, called iron pyrites or freestone, because some varieties of it absorb oxygen from the air and become hot, is a very abundant mineral. It forms cubic, octohedral, or dodecahedral crystals, of a yellowish colour and metallic lustre. When heated, it yields half its sulphur as a sublimate, but as the mineral generally contains arsenic, sulphur thus obtained is only used when better cannot be procured. Magnetic pyrites, Fe₃S₄, is characterized by its magnetic properties.
With carbon, iron forms two important compounds, which, however, contain very little carbon. These are cast-iron, which contains from 2 to 4 or 5 per cent., and steel, which contains only 1 or 2 per cent. of carbon. The former is hard, fusible, and brittle, but may be cast into any shape. The latter is sufficiently fusible to be cast if required, hard and elastic, as well as tough, which properties fit it for springs and cutting instruments. Both are made by simply heating iron in contact with charcoal.
No definite compound of iron with phosphorus is known; but a very small amount of phosphorus destroys all the good qualities of iron.
32. Manganese.
Symbol Mn. Equivalent = 27.6.
This metal appears to accompany iron; for while the ores of iron almost always contain traces of manganese, the ores of manganese contain traces of iron or even larger quantities. The metal itself is little known, but may be got by heating to intense whiteness oxide of manganese with charcoal. It is fusible with extreme difficulty, and so brittle as to be of no use in the metallic state. In appearance it resembles iron. Its density is 8000.
The only important compounds of manganese are its oxides, especially the deutoxide or peroxide. This occurs in considerable quantity in veins and nodules, in the form of black prismatic crystals, or as a crystalline mass with a black streak. One variety of it, called wad, is earthy in aspect. It also occurs hydrated, when it is more brown, and has a brown streak. The hydrate is less valuable than the pure oxide. Peroxide of manganese is much used in the manufacture of bleaching powder, and also by chemists in preparing oxygen and chlorine. Its formula is MnO₂, and it is a neutral or indifferent oxide.
Peroxide of manganese, MnO₂, is obtained by heating the carbonate, MnO₂CO₃, in a current of hydrogen; it is of a grass-green colour, and unless it be very compact, attracts oxygen from the air, and passes into peroxide. It is a powerful base, and forms salts which are colourless, or have a slight pink tinge. Alkalies produce in them a white precipitate of hydrated protoxide, rapidly passing into the brown hydrated peroxide by absorption of oxygen. Carbonated alkalies cause a white precipitate of carbonate of protoxide, which in drying becomes very slightly coloured, but is not altered in composition. Sulphuret of ammonium causes a flesh-coloured precipitate of hydrated sulphuret, while bleaching solution, and ozonized air, precipitate hydrated peroxide. This action of bleaching liquor is employed in calico-printing, to give a fine bronze brown.
Sesquioxide of manganese, Mn₂O₃, is left when the peroxide is heated to redness in close vessels. It is of a pale brown, and in its relations analogous to sesquioxides of aluminium and iron. It gives to glass an amethyst colour, and is believed to be the cause of the colour of the amethyst.
Red oxide of manganese, Mn₂O₄, is left when any oxide is ignited in open vessels. It seems to be a compound of protoxide and sesquioxide, analogous to magnetic oxide of iron.
Manganic acid, MnO₃, is formed in the same way as ferric acid; and its solution and that of its salts have a fine deep emerald green colour. Manganate of potash, KO₂MnO₄, is isomorphous with sulphate of potash. Its fine green solution cannot be preserved, but, like that of the ferrate, loses oxygen, while peroxide is deposited. But if diluted with hot water, the colour changes from pure green to bottle-green, olive-green, bluish-green, bluish-purple, and finally to a splendid reddish-purple, which belongs to the salt of another acid, permanganic acid.
Permanganic acid, MnO₄, is obtained in combination with potash, by adding hot water to the solution of the manganate. When the change is complete, a brown precipitate of hydrated peroxide settles, and the clear red solution, evaporated to a small bulk, yields beautiful bronze-coloured crystals of the permanganate, which have a metallic lustre; from the intensity of their purple colour, one small crystal will give to a quart of water a fine deep purple tint. This salt is much more permanent than the green manganate, but is rapidly deoxidized by all organic substances. In fact, it is a most powerful oxidizing agent, and produces peculiar results, from the nature of its composition, and the presence of an alkali. It is used in organic research. Its formula is KO₂MnO₄, and its formation from the green manganate is as follows: \(3(KO₂MnO₄) = MnO₄ + 2KO₂ + (KO₂MnO₄)\), so that the liquid becomes alkaline from free potash, and peroxide is separated. The action of this salt on sugar will serve as an example of its action on organic substances, by which acids are generally formed which combine with the potash. We shall suppose the sugar to be dry grape sugar, C₁₂H₂₂O₁₁. One eq. of sugar, with 6 eqs. of the salt, yield 12 eqs. of peroxide, 12 of water, and 6 of oxalate of potash. This proves that no part of the carbon in sugar can be in the form of carbonic acid, as some have supposed. For we get all the carbon as oxalic acid; and as that acid contains less oxygen than carbonic acid, it is impossible that it can have been formed from carbonic acid by means of a powerful oxidizing agency.
There are two chlorides of manganese, the protocloride Mn Cl, and the perchloride Mn Cl₂, corresponding to permanganic acid. The protocloride, from which all the salts of manganese are obtained, is obtained pure from the solution made in preparing chlorine by the action of hydrochloric acid on the peroxide. This solution contains protocloride of manganese, and sesquichloride of iron. One part of it is precipitated by carbonate of soda, and the washed precipitate, consisting of carbonate of protoxide of manganese with sesquioxide of iron, is added to the remaining solution and boiled. The protoxide in the precipitate expels the iron from the solution, so that, if the proportion of the solution precipitated has been rightly calculated, the whole manganese is now found in the liquid, and all the iron in the precipitate. It is best to manage it so that a little manganese remains in the precipitate, for in that case no iron can remain in the liquid, provided the iron has been in the state of sesquichloride or sesquioxide. This very beautiful process, in which one part of an impure solution is made to purify the whole, itself included, depends on the fact that protoxides, even in the form of insoluble carbonates, expel sesquioxides from their solutions. The solution must first be rendered neutral by evaporation to dryness, for free acid would prevent the result. A solution of protocloride of manganese is thus obtained quite free from iron, and containing only traces of copper, cobalt, and nickel. The first is separated by hydrosulphuric acid; the two others by a few drops of sulphuret of ammonium. From the pure chloride, which forms pink crystals, all the salts of manganese may easily be prepared.
The perchloride is volatile, and its vapour is of a greenish-yellow colour. It has not been much studied, but it is said to decompose the vapour of water, producing a purple cloud of minute particles of permanganic acid, along with hydrochloric acid.
Protosulphuret of manganese, Mn S, is formed as a flesh-coloured hydrate, when sulphuret of ammonium is added to the salts of protoxide of manganese. This appearance is quite characteristic of the pure salts of manganese.
It is worthy of notice, that while 1 eq. of manganese is isomorphous with 1 eq. of sulphur in the manganate of potash, isomorphous with sulphate of potash, 2 eqs. of manganese are isomorphous with 1 eq. of chlorine in the permanganate, isomorphous with perchlorate. The four salts are as follow—Sulphate of potash, KO, SO₄. Perchlorate of potash, KO, ClO₄. Manganate of potash, KO, Mn O₄. Permanganate of potash, KO, Mn O₅. This seems to indicate that our equivalent of chlorine ought to be halved, as it is on the Continent, when the formula of the perchlorate would be, KO, Cl₂O₄. Such a change, however, would imply the halving of the equivalents of bromine, iodine, hydrogen, and many metals; and although it may ultimately be adopted, at present it would cause confusion.
Iron and manganese form a group of two, with many points of analogy, and remarkable in this, that their atomic weights are almost if not exactly the same. We have now to examine two similar pairs.
The first of these includes zinc and cadmium. These metals are usually found, like the two last, together, and the analogy between them is very strong. Both are obtained from the chief ore of zinc, calamine, or silicate of oxide of zinc, and both are volatile at a red heat.
Zinc is a crystalline, easily-fusible metal, of a bluish-white colour, specific gravity about 7000. It melts at a low red heat, and if heated more strongly is converted into vapour, which takes fire and burns with a greenish-white flame, producing the oxide, a large part of which is carried upwards by the heated current, and deposited in light white flocks, called Lana Philosophorum. The oxide remaining in the crucible, when washed from any particles of metal, is pure, and is not in itself volatile. The metal is not malleable when cold, but is broken, although not very easily, by the hammer. At 300° it may be rolled into plates or sheets, which are used instead of sheet lead.
There is only one oxide of zinc, the protoxide, Zn O, which is prepared by burning the metal, or precipitated as a hydrate by the alkalies, an excess of which redissolves it. The best way is to precipitate it as carbonate, and to ignite that salt, when the oxide is left. While hot, it is yellow, but becomes white on cooling. It is distinguished from alumina in solutions by its ready solubility in excess of ammonia. Its salts are colourless and generally isomorphous with those of magnesia. The sulphate of zinc is so like that of magnesia, that its density alone distinguishes the two salts, unless we apply chemical tests. Solutions of zinc give, when quite neutral, a white precipitate of hydrated sulphuret with hydrosulphuric acid, but in acid solutions this test does not act. Sulphuret of ammonium produces, in neutral solutions, the same compound more abundantly. Ferrocyanide of potassium causes a white precipitate, and the action of caustic and carbonated alkalies has been already mentioned. The salts of zinc have a styptic metallic taste. The sulphate, acetate, and carbonate, as well as the oxide, are used in medicine. The sulphate is astringent, and in large doses emetic and poisonous. It is much used as a collyrium.
There is only one chloride, the protocloride, Zn Cl, formed when zinc is dissolved in hydrochloric acid. It forms a crystalline deliquescent mass, which, in solution, is used to preserve anatomical preparations, and to prevent decay in wood, according to Sir W. Burnett's method.
The iodide, Zn I, is made by the action of an excess of zinc on iodine under water, when the compound dissolves. It is used in medicine.
The sulphuret, Zn S, or zinc blende, is a common mineral in Cornwall and other mining districts. It forms dense black crystals, and when converted into oxide by roasting, yields the metal when heated with charcoal. The white hydrated sulphuret, formed in solutions of zinc by sulphuret of ammonium, when heated, loses water, and becomes black.
Zinc is much used in the form of sheets and pipes, not having the poisonous properties of lead. It is also a constituent of brass and of German silver. One of its chief uses now is the formation of galvanic batteries, in which plates of zinc are placed alternately with those of copper, or of platinized silver. For the purposes of the electric telegraph and the electrotype zinc is therefore most valuable. Chemistry. Carbonate of zinc prepared by a peculiar process has lately been introduced under the name zinc white, as a substitute for the poisonous white lead.
34. Cadmium.
Symbol Cd. Equivalent = 56.
The preparation of this metal from the common ore of zinc, of which it constitutes from 1 or 2 to 10, 12, or even 15 per cent., has been described under zinc. Cadmium also occurs in very small quantity as sulphuret, or cadmium blende, in fine orange crystals, of an octahedral form, first observed in trap rock in the west of Scotland by Lord Greenock, and hence called, as a mineral, Greenockite. In this rare ore no zinc is present.
Cadmium has a darker gray colour than zinc, and is very fusible and malleable. Its specific gravity is 8700. It is more volatile than zinc, and very combustible at a high temperature. Like zinc it forms but one oxide CdO, chloride CdCl, sulphuret CdS, &c. Its salts, like those of zinc, are astringent, styptic, and emetic. Sulphate of cadmium is an excellent collyrium. Cadmium is reduced to the metallic state from its solutions by zinc, and this furnishes a beautiful method for its purification. The oxide of the brown blaze of zinc works contains much zinc and some cadmium. It is dissolved in hydrochloric acid or sulphuric acid, and the acid solution in a platinum vessel acted on by a piece of zinc. The reduced cadmium adheres to the platinum, and after being washed may be dissolved off by hydrochloric acid. Another character of its salts is, that their acid solutions give with hydrosulphuric acid a fine orange yellow precipitate of sulphuret of cadmium. In this point it agrees with arsenious acid; but there is no difficulty in distinguishing between a basic oxide, such as oxide of cadmium, which forms an insoluble carbonate and is itself insoluble in water, and a soluble acid like arsenious or arsenic acid.
Zinc and cadmium form a pair of closely analogous metals, and the atomic weight of cadmium is not far from double that of zinc. It is probable that both metals will be used to coat the surface of other metals as we coat copper with tin; for already lead has been successfully coated with both, and even iron has been coated with zinc, under the name of galvanized iron. The two metals in question have the advantage of not being poisonous, as lead and copper are.
The next pair is even more remarkable for the analogy between them. The metals are cobalt and nickel. Like the metals of the two preceding pairs they are found associated, the ores of the one always containing more or less of the other. They are both as infusible as iron and manganese, and have more analogy to them than to zinc and cadmium. Indeed, there is a curious relation between them; for while cobalt and nickel are found in meteoric iron, and are like iron naturally magnetic, iron is always found in the ores of nickel and cobalt, often in large proportion. Again, there are traces of cobalt and nickel in the ores of manganese, except in a very few instances. Lastly, the atomic weight of all four metals is nearly the same, varying only from 27·6 to 29·6.
35. Cobalt.
Symbol Co. Equivalent = 29·5.
The metal is found chiefly as arseniuret, along with arseniurets of iron and nickel; also as sulphuret. It is best purified from arsenic, by melting with sulphur and alkalis, when it is converted into sulphuret; or the arseniuret is dissolved in nitric acid, and the arsenic precipitated as sulphuret by hydrosulphuric acid, which does not precipitate cobalt, nickel, or iron in acid solutions; but this latter process is very tedious. When a solution is obtained free from arsenic it is boiled with nitric acid to convert the iron into sesquioxide. Excess of alkali is then added, and the precipitate, consisting of protosides of cobalt and nickel, and sesquioxide of iron, is acted on by oxalic acid, which forms with the two first insoluble salts, with the last a soluble one. The iron is thus entirely removed by washing, and a pale pink powder is left, a mixed oxalate of cobalt and nickel, the former predominating. When the ore of nickel (arseniuret) is treated in the same way, the mixed oxalate is pale green, the nickel predominating. This powder is dissolved in liquor ammonia, and the dark red solution exposed to the air in a loosely-covered jar. As the excess of ammonia is dissipated, a green salt is deposited, oxalate of nickel and ammonia, while the colour of the liquid becomes a pure wine red, and it contains now only a similar but soluble double oxalate of cobalt and ammonia. This is dried upon ignited, or boiled with caustic potash, and yields pure black sesquioxide of cobalt. If the metal is wanted, this oxide is dissolved in hydrochloric acid, precipitated by a fixed alkali, and reconverted into oxalate, which is now of a pure pink colour, and when ignited in a covered crucible with a small aperture for gas, leaves the pure metal either spongy, or if the heat be high enough, melted into a button. The action of heat on the oxalate is as follows, $\text{CoO} + \text{C}_2\text{O}_4 = 2\text{CO}_2 + \text{Co}$. The oxalate of nickel and ammonia is ignited, and leaves oxide of nickel, from which the metal may be prepared exactly as cobalt is.
Cobalt is gray, brittle, very infusible—specific gravity 8500. Its protoxide CoO is a powerful base, has an ash-gray colour, and forms salts, which are either pink, crimson, or blue. Its solutions are pink, and give with alkalies a lilac hydrate, changing to brown; a permanent lilac carbonate with carbonated alkalies, and a black sulphuret with sulphuret of ammonium. Salts of cobalt, ignited with alumina, give it a fine smalt-blue colour. In fact smalt or zaffre is the silicate of oxide of cobalt, named zaffre (or sapphire originally, Italian zaffir) from its colour. It is got by roasting the ores of cobalt with sand, and is much used to give the blue colour to chinaware, and also to be added in small quantity to paper to improve its colour. There are several oxides of cobalt, but the protoxide is the most important.
The protocloride, CoCl, forms beautiful deepred crystals, which, when heated, melt to a deep rich blue liquid. Traces made on paper with a very dilute solution of this salt are invisible when dry, their pink colour being very pale. But on being warmed they turn blue and become visible, again disappearing on cooling, moisture being absorbed. This is one of the oldest and best known sympathetic inks, and has this advantage that the characters may be made to appear and disappear any number of times, provided the heat applied be not too strong.
36. Nickel.
Symbol Ni. Equivalent = 29·6.
The preparation of this metal has been given under cobalt. It is about as difficult to melt as iron, is of specific gravity 8800, has a whiter colour, and is malleable and magnetic, so that needles for the compass may be made of it, and these do not rust as steel is apt to do. But the metal is principally used as the chief ingredient in German silver. The more nickel this alloy contains, up to a certain point, the more it resembles silver in colour and lustre, as well as in permanence. The other ingredients are zinc and copper.
Protoside of nickel, NiO, is a powerful base, its salts are all green, and their colour is complementary to that of the corresponding salts of cobalt. Its solutions are easily recognised by their colours, and by the pale apple-green hydrate and carbonate produced by caustic and carbonated alkalies. Ammonia in excess redissolves the precipitated hydrate, forming a sapphire-blue solution. Sulphuret of ammonium causes a black precipitate of the sulphuret NiS. From salts of copper, which are redissolved by ammonia, with a deep Chemistry violet-blue, and precipitated black by sulphuret of ammonium, those of nickel are distinguished by not being precipitated, if free acid be present, by hydrosulphuric acid, and by the action of ferrocyanide of potassium which gives with copper a chestnut-brown precipitate. The colour of the solution of copper too is generally blue.
Nickel forms a peroxide which is not of much interest, nor are the other compounds of nickel very important. The astonishing analogy between nickel and cobalt in so many points, while they differ in the colour of their compounds, as well as the fact that they always occur associated, and that they seem to accompany iron, not only in the mineral kingdom, but also in meteoric iron, and that both are magnetic, seem to indicate some hidden relations of an interesting kind.
37. Tin.
Symbol Sn (Stannum). Equivalent = 59.
This metal is the last of the present group, and stands here by itself, although it has many points of analogy with zirconium, and perhaps titanium, in its compounds.
Tin occurs chiefly as deoxidite or peroxide, sometimes called stannic acid, from its weak acid properties, in the form of rounded or water-worn crystals, called tinstone, or stream tin, being found in the beds of streams in tin districts. It is easily reduced by heating with charcoal, the metal being very fusible. Tin also occurs as tin blende or sulphuret, which is roasted and then heated with carbon.
The metal has a yellowish-white colour and bright lustre, and melts at 440°. Its specific gravity is 7290. It is a most valuable metal, being used to make pipes and sheets or leaves, also to coat iron plate, forming tinned iron, commonly called tin-plate, and to form with copper the various kinds of bronze and bell metal; with lead, pewter and solder.
When heated to whiteness in air, it burns into oxide, and may also be easily oxidized by nitric acid. It forms two oxides—the protoxide SnO, a somewhat weak base, and the deoxidite SnO₂, which has rather weak acid properties. Peroxide of tin, or stannic acid, seems to exist in two forms; in one it dissolves easily in acids, in the other it is insoluble. The latter is supposed to have 6 times the equivalent of the former, and to be Sn₆O₇.
There are two chlorides corresponding to the two oxides, SnCl and SnCl₂, both of which are much used in dyeing and calico-printing to brighten the colours. It is only by means of tin that cochineal is made to yield the fine colour given to scarlet cloth. The protocloride of tin crystallizes very readily. The perchloride is a volatile fuming liquid, but is commonly prepared in aqueous solutions by dissolving tin in nitro-hydrochloric acid. The protocloride is formed when tin is heated with hydrochloric acid, hydrogen being disengaged.
Iodide of potassium strikes a deep red colour with salts of tin, from the formation of an iodide.
There are two sulphures of tin. The protosulphuret SnS, is dark brown or black. The bisulphuret has a dirty yellow colour, and some degree of metallic lustre; it used to be called aurum musivum. These sulphures are precipitated from the solutions of tin by hydrosulphuric acid.
Tin is thrown down in beautiful metallic crystals, from its solutions, by zinc.
GROUP VI.
Acidifiable Metals.
The next group of metals is characterized by a remarkable tendency to form acids with oxygen, and by the absence of basic protoxides. They are eleven in number, but only three of them are of practical importance, and one or two of the others are hardly known. Most of the acids of this class of metals are teroxides, and most of the metals form volatile chlorides.
38. Chromium.
Symbol Cr. Equivalent = 267.
This metal, which is in some points analogous to iron and manganese, connects this group with the last. It is chiefly found in two forms, as chromic acid, combined with oxide of lead, in the beautiful and scarce red lead ore of the Ural, and as sesquioxide, combined with sesquioxide of iron in the more abundant chrome iron ore. The metal is little known. It is very infusible, hard, and brittle. Specific gravity about 6000.
It forms two oxides—the sesquioxide or green oxide, Cr₂O₃, and the orange-red chromic acid, CrO₃. The former, like other sesquioxides, is a weak base. It is obtained from bichromate of potash, by heating it with carbonate of soda and sal-ammoniac, when the acid is deprived of half its oxygen by the hydrogen of the ammonia. Water dissolves the saline matter from the residue, and leaves the sesquioxide of a fine deep green. It is precipitated from its solutions as a bluish-green bulky hydrate. Like all sesquioxides, it has a great tendency to form double salts, and in fact may be substituted for alumina in alum without altering the form of the salt. Chrome alum, as it is called, is of a dark reddish-purple by transmitted light, black by reflected light, green in powder and in solution, of a mixed green and red by day-light, pure red by candle-light. Another beautiful double salt, the oxalate of chromium and potash, is azure-blue by transmitted sun-light, red by transmitted candle-light, black by reflected light. The remarkable action of these salts on light has been described by Brewster.
Chromic acid, CrO₃, is formed when chrome iron ore is heated with nitre. The sesquioxide, being oxidized, forms the acid, which unites with the potash of the nitre, forming a lemon-yellow neutral chromate, KO₃CrO₃. The strong solution of this salt, mixed with nitric acid, loses half its potash, and deposits beautiful orange red crystals of the bichromate of potash, KO₂CrO₃. Both these salts are much used in calico-printing. To obtain the acid pure, a cold saturated solution of bichromate is mixed with oil of vitriol; and the mixture, on cooling, for heat is developed, deposits beautiful red acicular crystals of the acid. These are drained on a fire-brick, excluding the air, and when dry, sealed up in a tube. If any sulphuric acid or bisulphate of potash adhere to them, they may be purified by dissolving them in a little hot water, adding some sulphuric acid, and recrystallizing.
Chromic acid is very soluble in water, even deliquescent. It oxidizes organic substances, such as alcohol or ether, with flame. One very convenient method of using it as an oxidizing agent is to heat the organic substance with bichromate of potash and sulphuric acid, when the action is more gentle. In all cases the acid is reduced to sesquioxide.
The salts of chromic acid are remarkable for their fine colours, which are yellow, orange, and red. The chromates of potash (neutral), baria, zinc, and lead (neutral), are of various shades of yellow. The bichromate of potash is orange. The dichromate of lead and the chromate of mercury are orange-red, and that of silver is deep red. The chromates of lead are used as pigments, and also formed on the cloth in calico-printing. The sesquioxide is used to give the beautiful green now so often seen on fine porcelain.
The chromates of potash are poisonous, and the workmen who make or use them suffer from ulcers on the hands of a peculiar kind. The solutions of these salts are antiseptic in a high degree. They may also be used like nitre to give to cotton or cloth the property of burning as in moxas.
There are two chlorides of chromium, a sesquichloride, which is of a peach-blossom colour, but forms a green solution and a volatile chloride, either a terchloride CrCl₃ or Cr₃Cl₇. But the latter is not well known. There is an oxychloride which is a volatile liquid of a dark red colour, acting violently on combustible substances, which is CrO₂. Chemistry. Cl, that is, chromic acid, in which 1 eq. of oxygen is replaced by chlorine, or else $2 \text{CrO}_3 + \text{CrCl}_3$, a compound of 2 eqs. of chromic acid with 1 eq. of terchloride. The proportions are the same, the latter being 3 times the former.
39. Vanadium.
Symbol V. Equivalent = 68.6.
This very rare metal is found as vanadic acid $\text{VO}_2$, combined with oxide of lead, and also in small proportions in some of the ores of iron. It forms three oxides, a protoxide $\text{VO}$, a deutoxide $\text{VO}_2$, and vanadic acid $\text{VO}_3$, which is analogous to chromic acid. The acid has a reddish orange colour, is sparingly soluble in water, and when fused forms on cooling very large crystals even from a small quantity. It is easily deoxidized and yields the deutoxide, which is a weak base, and forms blue salts. The protoxide is black, and is not known to form salts. Vanadium forms two chlorides, a bichloride $\text{VCl}_2$, and a volatile terchloride $\text{VCl}_3$. Vanadium is too rare to be applied to any useful purpose.
40. Molybdenum.
Symbol Mo. Equivalent = 96.
This metal occurs as molybdic acid, combined with oxide of lead, and also as tersulphuret of molybdenum. The metal is little known. Molybdic acid, $\text{MoO}_4$, corresponds to chromic acid. Its only use is as a test for phosphoric acid, with which, when heated in solution with it, it forms a peculiar yellow precipitate. It is used in the form of molybdate of ammonia.
Like chromium, molybdenum forms a volatile terchloride and an oxychloride. But we need not dwell on this metal here. There is an oxide, with less oxygen than the acid, which has a fine blue colour.
41. Tungsten.
Symbol W (Wolfram). Equivalent = 95.
This metal is of no great interest. It is found as tungstic acid, combined with lime, or with oxides of iron and manganese, the former being the mineral tungsten, the latter wolfram.
Tungstic acid, $\text{WO}_4$, is a nearly insoluble yellow powder. Like molybdenum, it forms, with less oxygen than in the acid, a blue oxide like indigo. This appears to be a compound of the acid with another inferior oxide, oxide of tungsten, which is black. Tungsten, too, forms a volatile terchloride, and an oxychloride.
42. Titanium.
Symbol Ti. Equivalent = 25.
This metal also occurs as titanic acid in the mineral rutile. According to some, the formula of the acid is $\text{TiO}_2$, while others make the acid $\text{TiO}_3$. From its analogy to oxide of tin, it is probable that the latter formula is correct. Like peroxide of tin, it exists in two forms, one of which is brown and insoluble in acids; the other white and soluble in hydrochloric acid. The white variety is used to form an enamel for artificial teeth. It was at one time thought that the copper-coloured cubic crystals occasionally found in the slag of iron furnaces, were metallic titanium; but these have been shown to contain nitrogen and cyanogen besides. This metal, like the two preceding, forms a volatile chloride. There appear to be two oxides, the sesquioxide and the acid, and two chlorides, sesquichloride and bichloride, corresponding to these. The solutions of titanic acid in acids are decomposed by boiling, the titanic acid being deposited; and when the acid is fused with alkalis, the fused titanate is decomposed by water, leaving an acid salt with large excess of acid.
The composition and properties of the acid and of the bichloride show a great analogy with tin; but these metals are easily distinguished, since the compounds of tin, heated on charcoal before the blowpipe, readily yield metallic tin.
43. Columbium.
Symbol Ta (Tantalum). Equivalent = 92?
This metal occurs in the form of columbic acid, $\text{TaO}_2$, in a few very rare minerals. Its properties are but imperfectly known; and it has recently been found to be associated with two other analogous metals, namely, 44. Niobium, and 45. Pelopon, which are still less known, but appear also to form acids with oxygen.
46. Antimony.
Symbol Sb (Stibium). Equivalent = 129.
This metal occurs as sulphuret, and as double sulphuret of antimony and silver; also as bournonite, a triple sulphuret of lead, copper, and antimony. It is obtained from the sulphuret by heating it with iron fillings, or with carbonate of soda, after roasting it. The metal is fusible at a moderate red heat, of a gray colour and very bright lustre; specific gravity 6800. At a white heat it is converted into vapour, and burns in air. It forms two distinct oxides, and these combine to form a third.
Teroxide of antimony, $\text{Sb}_2\text{O}_3$, is a weak base. It is obtained by pouring the terchloride into water, when an oxychloride is formed. This is boiled with excess of carbonate of soda, and leaves the teroxide as a grayish-white powder. It has a great tendency to form double salts, such as tartar emetic, which is a tartrate of antimony and potash. Its solutions give with hydrosulphuric acid a characteristic brownish-orange precipitate of hydrated tersulphuret.
Antimonic acid, $\text{Sb}_2\text{O}_5$, is obtained by the action of nitric acid on the metal; it resembles the teroxide in appearance, but has weak acid properties. Both oxides are used in medicine.
There is another oxide, sometimes called quadroxide, but which appears to be $\text{Sb}_2\text{O}_4 = \text{SbO}_2$, $\text{SbO}_3$, an antimoniate of the teroxide. It is formed by heating the antimonic acid.
Antimony forms with hydrogen a gaseous compound, probably $\text{SbH}_5$, analogous to phosphuretted hydrogen. It is not yet known in a state of purity, but only mixed with hydrogen. It is formed when hydrogen is disengaged in a solution containing antimony. The mixed gas burns with a yellow flame, giving off fumes of oxide, and which deposit metallic spots of antimony on glass or porcelain held in the flame. In these characters, antimony agrees with arsenic, and, indeed, it may be said to form with phosphorus and arsenic a group of three, like some of those we have already seen.
There are two chlorides of antimony, the terchloride, $\text{SbCl}_3$, and the perchloride, $\text{SbCl}_5$, both volatile; the former semi-solid at ordinary temperatures, and hence called butter of antimony. Mixed with water, it deposits an oxychloride, $\text{SbCl}_3 + 2 \text{SbO}_3$, called powder of galagroth, which is used in preparing the oxide as well as tartar emetic. The terchloride is formed by the action of hydrochloric acid on the tersulphuret.
There are also two sulphurets, the tersulphuret $\text{SbS}_3$, and persulphuret $\text{SbS}_4$; the former is the ore of antimony, and is dissolved by hydrochloric acid, yielding the terchloride and hydrosulphuric acid gas, $\text{SbS}_3 + 3 \text{HCl} = \text{SbCl}_3 + 3 \text{HS}$.
The compounds of antimony are much employed in medicine; and the metal is a chief ingredient in the alloy used for types, in which it is combined with lead and a little tin, and in some alloys with tin used for various purposes.
47. Arsenic.
Symbol As. Equivalent = 75.
This metal is found chiefly combined with sulphur, and also Chemistry, with metals, such as cobalt and nickel. It likewise occurs as arsenic acid, AsO₃, combined with various oxides. When the minerals containing it are roasted, part of it is sublimed in the metallic state, and part as arsenious acid AsO₂, which is consequently obtained in very large quantities from the ores of cobalt and nickel. To obtain the metal from this acid, it is simply heated with charcoal, when the metal sublimes and forms a bright metallic crust. Its density is 5800. Under the ordinary pressure, it is converted into vapour before reaching its melting point. Its vapour has a strong garlic odour, and is very poisonous. It burns when heated in air, forming arsenious acid, which also sublimes as a white crystalline powder.
Arsenious acid, AsO₂, is volatile; its vapour has no smell, unless when heated on charcoal, when it is reduced to the metallic state, and it is the metallic vapour the smell of which is then observed. It is sparingly soluble in water, and its solution gives, with excess of lime-water, a white precipitate of arsenite of lime; with ammoniacal-sulphate of copper, a grass-green precipitate of arsenite of copper, or Scheele's green; with ammoniacal-nitrate of silver, a lemon-yellow precipitate of arsenite of silver; and with hydrochloric acid, a bright yellow sulphuret, AsS₂. By these characters this substance when pure is easily recognised; and from its very poisonous nature, and the facility of procuring it, poisoning by its means is so frequent, that it has to be sought for oftener than any other poison.
The best antidote to it is the administration of a large quantity of moist hydrated sesquioxide of iron, which has the property of forming with it an insoluble and inert arsenite of iron. Calcined magnesia has a similar effect.
When arsenious acid has to be sought for in mixed fluids, the above tests are inapplicable, except the last, which may be used to separate the arsenic from the mixed fluid, after adding an acid and filtering. The impure sulphuret thus obtained is decomposed by heating it with a mixture of charcoal and carbonate of potash, or with cyanide of potassium, and the metal sublimed. It is recognised by its volatility and the odour of its vapour, but it may also be oxidised and the tests applied. Even when the acid is pure, we ought always to reduce at least a part of it to metal, as the most characteristic property. Only antimony at all resembles it in this particular, but we shall see presently that these two metals are easily distinguished.
Where the quantity of arsenic present is very small, the method of Marsh, in which it is converted into arseniuretted hydrogen, must be employed as the most delicate and the most certain. We shall describe this presently, under the head of arseniuretted hydrogen.
Arsenic acid, AsO₃, corresponds to phosphoric acid as arsenious acid does to phosphorous acid. It is formed by heating arsenious acid with nitric or nitro-hydrochloric acid. It is very soluble, very acid, and very poisonous. Its salts are exactly similar to and isomorphous with those of phosphoric acid.
When hydrogen is disengaged in a solution containing arsenious acid, there is formed arseniuretted hydrogen, AsH₃, mixed with hydrogen. The gas is obtained purer, but still mixed with some hydrogen, by the action of hydrochloric acid on an alloy of tin and arsenic. It has a most offensive alliaceous smell, and burns when heated in air, with a pale flame, producing arsenious acid and water. It is extremely poisonous, and several chemists have lost their lives from inadvertently inhaling a little of it.
When this gas, even mixed with a large excess of hydrogen, is passed through a tube, part of which is red-hot, it is entirely decomposed, and a ring of metallic arsenic is deposited just beyond the hot part of the tube. On this property is founded Marsh's process for detecting arsenic.
The suspected liquid is added to diluted sulphuric acid, and zinc is introduced. The gas is then passed through a narrow tube, and a slow but constant current of it is kept up. As soon as all the air is expelled from the tube, a part of it is heated to redness, and if there be but a trace of arsenic present, a ring soon appears. Or the gas may be burned at the end of the tube without heating it in the tube, and a cold piece of glass or porcelain held in the flame, which, if arsenic be present, will deposit metallic stains of that metal. The former method is the best, as the whole arsenic may in time be collected in one ring. Under similar circumstances, antimony also forms a ring of metal, but the arsenical ring is sublimed by a moderate heat, and if air be present is changed into arsenious acid, easily recognised by its octahedral crystals, its volatility, and by other tests. The antimony is with difficulty volatilized, and if oxidized, the oxide remains, and is not crystalline. Nitric acid dissolves the arsenic, but not the antimony.
This method of detecting arsenic is so delicate, that by its means arsenic is found where it was not before suspected. We often find it in the commercial sulphuric acid, hydrochloric acid, and zinc, the very substances we use in the process. Hence, before introducing the suspected fluid, we must always try the acid and zinc first for a time. If no ring appear, and if, on adding the suspected liquid, the ring be at once formed, we may safely conclude that the arsenic comes from that liquid. But without this precaution, we dare not make any such statement.
There is only one chloride of arsenic, a terchloride, AsCl₃, which is volatile.
There are three sulphurets of arsenic. Realgar, which is reddish-brown, AsS₂; orpiment, which is yellow, AsS₂; and the persulphuret, which is pale yellow, AsS₃. The two former are found in nature.
The reader has no doubt remarked the analogy between the chemical relations of antimony and arsenic and those of phosphorus. Indeed, no two elements are so analogous in this respect as arsenic and phosphorus, save that one is metallic, the other not. There is a resemblance, however, even in physical properties for the odour of phosphorus closely resembles that of arsenic. These three elements, in spite of one being non-metallic, form a group distinguished by forming oxides with 3 and 5 eqs. of oxygen, and gaseous compounds of a fetid odour with 3 eqs. of hydrogen.
48. Tellurium.
Symbol Te. Equivalent = 64·2.
This metal forms one of another remarkable group of three, the two others being non-metallic, namely, sulphur and selenium. This case and the preceding, show that there is no essential and absolute division between metals and non-metallic bodies.
Tellurium is found, but very rarely, combined with gold, silver, lead, and bismuth, in the Transylvanian mines. In appearance it resembles antimony, and its specific gravity is 6·260. With oxygen it forms two acids, tellurous acid, TeO₂, and telluric acid, TeO₃, corresponding to sulphurous and sulphuric acids. With hydrogen, it forms a gaseous compound, H₂Te, corresponding to hydrosulphuric acid, and resembling it in its properties and its action on metallic solutions.
Tellurium is volatilized by an intense white heat. It is chiefly interesting from its analogy to sulphur and selenium; but its rarity prevents it from being applied to useful purposes, although it seems likely to have a powerful action on the animal system.
**GROUP VII.**
This group has no peculiar character, from which it can be properly named, but is intermediate between group 5 and the next or last group, that, namely, of the noble metals. The number of metals in it is five, namely, bismuth, uranium, copper, lead, and mercury. Their attraction for oxygen is less than that of the metals of group 5, but still considerable. The oxides of one of them, mercury, are reduced by heat alone, thus connecting these metals with the noble metals. The protoxides, and in some cases higher oxides, are basic.
49. **Bismuth.**
Symbol Bi. Equivalent = 71 t or 106 t
This metal is found in the metallic state, and as sulphuret, also combined with tellurium. It is obtained entirely from the native metal, which, being very fusible, is separated from its gangue or matrix by fusion. It contains a little sulphuret, also sulphurets of other metals and arseniurets, but is easily purified by heating with ½ th of its weight of nitre. The sulphur, arsenic, and other metals are oxidized and combine with the potash, as does also a little bismuth; the rest forms a pure button of metal below the saline mass. Bismuth is very crystalline, and may be obtained in fine crystals by melting a mass of it, and when it is half solidified, breaking the crust and pouring out the liquid part. The hollow mass is found lined with fine hollow rhombohedral crystals, not far removed from the cube in their angles. Its colour is reddish-white; its specific gravity 9000. It melts at about 507°, and expands in solidifying. It is volatile at a very intense heat.
Bismuth forms two oxides: 1. A basic oxide, which is thought by some to be a protoxide, Bi₂O₃, in which case the equivalent of the metal is 71; but which others regard as a sesquioxide, Bi₂O₄, which makes the equivalent of the metal 106. It is a weak base, and its salts are decomposed by water, which dissolves very acid salts, leaving insoluble sub-salts. This is particularly the case with the nitrate, which, diluted with water, deposits a fine white crystalline powder of sub-nitrate, used as a white paint for the face. It is, however, very liable to be blackened by hydrosulphuric acid and other analogous compounds of sulphur. The salts of bismuth are recognised by the action of water and that of hydrosulphuric acid.
2. A peroxide, which has weak acid properties, and is also called bismuthic acid. It has a light red colour, and has not been much studied. If the basic oxide be Bi₂O₃, the acid is Bi₂O₄; but if the former be Bi₂O₄, the latter is probably Bi₂O₅. There seems to be an intermediate oxide, a compound of the acid with the base.
Chloride of bismuth is volatile, and, taking the larger equivalent, its formula is Bi₂Cl₄. It dissolves in hydrochloric acid, but the solution is decomposed by water, which throws down an oxychloride, Bi₂Cl₄ + 2 (Bi₂O₃, 3 HO). This powder is pearl white, used like the subnitrate as a cosmetic.
Sulphuret of bismuth, Bi₂S₃, occurs in nature, and is isomorphous with sulphuret of antimony.
Bismuth forms with lead and tin alloys of remarkable fusibility. That with 1 part of lead, 1 of tin, and 2 of bismuth, melts at 201°; that with 5 parts of lead, 3 of tin, and 8 of bismuth, melts at 209°. These alloys are used for taking casts for electrotyping, and for various other purposes.
50. **Uranium.**
Symbol U. Equivalent = 217-2.
This metal is found as an oxide, combined with oxides of iron, lead, copper, and other metals, along with silica, in the mineral pitchblende; and also as a phosphate of uranium and lime, in uranite. The pitchblende is acted on by nitric acid, and the solution purified from lead, copper, and arsenic, by hydrosulphuric acid. The nitrate of uranium is then crystallized. This salt, which forms beautiful yellow crystals with green reflection, when heated leaves an oxide. This, mixed with charcoal, and heated in a current of chlorine, gives a volatile protocloride, U Cl, in dark green crystals. These, heated with potassium, yield the metal as a black powder, parts of which, by the heat evolved, are brought into a compact state, and exhibit a silvery lustre. Heated in air, it burns vividly, producing the oxide. It is permanent at ordinary temperatures, and appears to be in some degree malleable. It only decomposes water at a high temperature.
Uranium forms two oxides, both basic, a protoxide, U O₂, and a sesquioxide, U₂O₃. The former is dark brown, and forms green salts; the latter is yellow, and forms beautiful yellow salts. From the circumstance that the salts of the sesquioxide differ in the amount of acid from those of all other sesquioxides—the sulphate, for example, being U₂O₃, SO₃—and not like that of alumina, Al₂O₃, 3 SO₃—it is supposed that the sesquioxide is really a protoxide, not of uranium, but of uranyl, U₂O₄. On this supposition, the salts of the sesquioxide are no longer anomalous. These salts give yellow precipitates with the alkalis, which are compounds of the sesquioxide with the alkalies, for that oxide has both weak acid and weak basic properties. Ferrocyanide of potassium produces in the salts of sesquioxide of uranium a fine rich brown precipitate.
The chloride, U Cl, has been already mentioned. There is an oxychloride U₂O₃ Cl, which may be regarded as the protocloride of uranyl. When heated with potassium it leaves not the metal but the protoxide, U O₂, or uranyl U₂O₄, which was long supposed to be the metal, and appears, in fact, to play the part of a metal.
Oxide of uranium is now much used to give to glass the beautiful yellow colour, with green reflection, so much admired in the Bohemian glass.
51. **Copper.**
Symbol Cu. Equivalent = 31-7.
This valuable metal occasionally occurs native, but its chief ores are the mixed sulphurets of iron and copper or copper pyrites, the carbonate or blue copper ore, and the compound of carbonate and hydrate called green malachite. The latter are easily reduced by heating with charcoal; the former is roasted so as to oxidize it and dissipate the sulphur, and the roasted ore is then heated with charcoal. This process is repeated, and at last pure copper is obtained. Another ore of copper, very easily worked, is the red oxide or suboxide. Lastly, in mines where sulphuret of copper is present, it is oxidized by the air into sulphate of protoxide, which is dissolved by the water filtering through the rocks. This water, where the sulphate is observed, is collected in reservoirs, and the copper precipitated by fragments of iron. The copper thus obtained is very pure, and has only to be melted.
Copper has a bright red colour and high lustre, of specific gravity from 8780 to 8960. It melts at a strong red heat, and at a white heat gives vapours which burn with a green flame. It is very malleable and ductile, and has much tenacity.
Copper is rapidly tarnished and covered with a green rust Chemistry, or verdigris, in moist air. At a red heat it is rapidly converted into the black protoxide.
Protoxide of copper, CuO, is black, and forms with acids blue or green salts, with water a blue hydrate. It is a pretty strong base. Its solutions are known by their colour, by the action of a rod of iron which is quickly covered with precipitated copper, and by the action of ammonia which first causes a pale blue precipitate of subsalt or hydrate, and when added in excess, redissolves this, forming a deep violet-blue solution. Potash and soda throw down the blue hydrate, which, when boiled, loses water and becomes black. Hydro-sulphuric acid gives a black precipitate of sulphuret, and ferrocyanide of potassium gives, in acid solutions, a chestnut-brown precipitate. The last is a most delicate and characteristic test, and by its means traces of copper have been found in most soils, as well as in plants, and in animal and vegetable food. Copper vessels are rapidly corroded by cold vegetable acids, but the same acids may be boiled in them without corroding the metal. As the salts of copper are very poisonous, this must be carefully attended to. Preserves of acid fruits, such as red currants, &c., are constantly boiled in vessels of copper, but must not be allowed to cool in them. Copper is sometimes improperly added to pickles to improve their green colour. Its presence is easily detected in the acid liquor by the ferrocyanide, or by introducing the blade of a knife. Several of the salts of copper are used in medicine. Sulphate of copper, or blue vitriol, is an escharotic externally, and an emetic in small doses given internally. The violet-coloured ammoniacosulphate of copper is used in epilepsy, and also as a test for arsenious acid.
Suboxide of copper, Cu₂O, is red and crystallizes in octahedrons. It is found in nature, and may be formed by heating the protoxide with copper filings, or by adding to a solution of sulphate of copper sugar and potash, till the precipitate at first formed is redissolved. On boiling, the suboxide is deposited as a fine deep red crystalline powder. It forms colourless salts, and a colourless solution in ammonia, but the latter solution absorbs oxygen from the air, and becomes violet-blue. The oxide gives to glass, when melted with it, a fine red colour.
Copper seems to form two oxides with more oxygen than the protoxide, a deutoxide and an acid. But these are very little known.
There are two chlorides of copper; the subchloride or dichloride CuCl₂, and the protochloride CuCl. The former is white and sparingly soluble. The latter is green and very soluble. It is formed by dissolving the protoxide in hydrochloric acid.
There are also two sulphurets corresponding to the two oxides and chlorides. The disulphuret, Cu₂S, is formed by melting together copper and sulphur. It is fusible and crystalline. The protosulphuret, CuS, is the black precipitate produced in salts of copper by hydrosulphuric acid. H₂S + CuO → H₂SO₃ + CuS. It rapidly attracts oxygen from the air, and is converted into sulphate. Copper pyrites consists of the disulphuret, combined with sesquisulphuret of iron, and mixed moreover with iron pyrites, or bisulphate of iron. From this mineral the greater part of the copper of commerce is obtained.
Copper forms many valuable alloys. With zinc or tin and a little tin or lead, it forms brass; with tin it gives bronze, bell metal, gong metal, and gun metal, according to the proportions. In the bronze used for medals, a trace of zinc is added.
52. Lead.
Symbol Pb (Plumbum). Equivalent = 1037.
This valuable metal occurs in various forms, but the only ores which are wrought are galena or sulphuret of lead, PbS, and carbonate of lead, PbO, CO₃. The latter is simply heated with charcoal. The former is roasted, when sulphurous acid is given off, and oxide of lead, PbO, and sulphate of lead, PbO, SO₄, are formed. A part of the ore is left unchanged; and on increasing the heat, a most remarkable reaction takes place between the unaltered ore and the oxide and sulphate. The reaction with the oxide is this: PbS + 2 PbO → SO₂ + Pb. With the sulphate it is this: PbS + PbO, SO₄ → 2 SO₂ + Pb. In both cases, metallic lead and sulphurous acid are the only products. When the ore is less pure, it is first roasted and then heated with iron, which removes the sulphur. The lead thus obtained frequently contains silver in sufficient quantity to repay its extraction.
Lead is a metal of a dark-gray colour and high lustre, quickly tarnished in air, but only superficially at ordinary temperatures. It is very soft, malleable, and ductile, but has little tenacity. Its specific gravity is 1144. It is easily melted, and when hot is rapidly oxidized, forming protoxide. The uses of lead are well known.
With oxygen lead forms three compounds, a suboxide PbO, a protoxide PbO, and a deutoxide having feeble acid properties, peroxide of lead or plumbic acid.
The protoxide, PbO, is formed when lead is heated rather beyond its melting point. It is a yellow powder called massicot. This, heated more strongly, melts, and on cooling forms a crystalline brownish-yellow mass, called litharge. Heated for a long time in air, massicot takes up oxygen and forms the red oxide or minium, a compound of plumbic acid with the protoxide. The protoxide is a strong base, isomorphous with baryta and lime. Its salts have a sweet taste, and are poisonous, more especially the carbonate. They are recognised by the following tests. Alkalies throw down a white hydrate, soluble in excess; carbonated alkalies a white carbonate; hydrosulphuric acid a black sulphuret; sulphuric acid and sulphates a white insoluble sulphate; and iodide of potassium a bright yellow crystalline iodide. The most important of its salts are the carbonate or white lead, the nitrate, the acetates, which are used in calico-printing, the latter also extensively in medicine, and the chromate, valued for its fine yellow colour.
Plumbic acid or peroxide of lead is obtained by acting on red lead with nitric acid. Red lead is PbO₂ = 2 PbO, PbO₂ and also PbO₂ = 3 PbO, PbO₂. The acid dissolves out the protoxide, and leaves the plumbic acid as a peacock-coloured dense powder. It combines with bases, and even forms crystalizable salts with some of them.
With chlorine, lead forms but one compound, a protochloride, PbCl. It is formed as a sparingly soluble white crystalline powder when hydrochloric acid or soluble chlorides are added to the salts of lead. The chloride, melted with the oxide, forms several oxychlorides, which are used as yellow pigments, under the names of mineral yellow, Turner's yellow, &c.
There is but one iodide, PbI, formed when iodide of potassium is added to a salt of lead. It is a bright yellow sparingly soluble powder, generally formed of minute scales, which dissolves in boiling water, forming a colourless solution. On cooling, large and beautiful scales of a golden lustre are deposited. They are regular hexagons.
There is also but one sulphuret, PbS, formed as a black powder when hydrosulphuric acid or a soluble sulphuret acts on salts of lead. It is the same substance with galena, the ore of lead, which forms cubic crystals of a metallic lustre, but very brittle.
Lead forms with antimony the alloy used for type metal; with tin it forms pewter and various kinds of solder.
53. Mercury.
Symbol Hg (Hydrargyrum). Equivalent = 200.
This metal is found native, and in the form of bisul- Chemistry. Pluret or cinnabar. The latter substance, when heated in iron bottles with iron filings, yields metallic mercury. The metal is liquid at all temperatures from -39° to about 600°, which is its boiling point. Below -39° it is solid. It has a bluish-white colour and bright lustre. Its specific gravity is about 1300. When heated to about its boiling point, in air, it absorbs oxygen, and forms the red oxide or deutoxide, which is again decomposed by a temperature somewhat higher.
Mercury forms two oxides, a protoxide and a deutoxide. The protoxide, HgO, is obtained by the action of potash on calomel, which is the protocloride, HgCl + KO = KCl + HgO. It has an ash-gray colour, and by the action of light is resolved slowly into deutoxide and metal, 2 HgO = HgO₂ + Hg. It is a base, and its salts give a dark gray or black precipitate with alkalies, a white one of calomel with hydrochloric acid or soluble chlorides, and a dirty greenish-yellow protiodide with iodide of potassium. They are reduced to the metallic state by copper and by other metals; also by protocloride of tin, which first forms calomel and then reduces it.
The peroxide or deutoxide, HgO₂, is also a base. It is obtained by heating the nitrate or either oxide till the acid is entirely expelled, taking care not to decompose the oxides. It is a very dark red, nearly black while hot, and light red when cold. The same oxide is formed slowly when mercury is kept at its boiling point in a vessel with a long neck, in which the vapours are condensed and fall back. Prepared in this way it is of a darker red, and is called oxidum hydrargyri rubrum per se, while that from the nitrate is called oxidum hydrargyri rubrum per acidum nitricum. The latter generally contains some subnitrate, and is more active as an escharotic. It is much used also in the form of ointment. Its salts give a yellow precipitate of hydrated peroxide with potash; a white with ammonia, which is a compound containing amide; and a fine scarlet periodide with iodide of potassium. Both the salts of protoxide and those of peroxide give a black precipitate with hydrosulphuric acid, which in the latter case is the bisulphuret, in the former a mixture of bisulphuret with the metal. The salts of the peroxide are reduced by the same reagents as those of the protoxide; by copper and other metals, by protocloride of tin, and by formic acid.
Mercury forms two chlorides: calomel, which is the protocloride, HgCl, a white, insoluble, heavy powder, formed by the action of hydrochloric acid or chloride of sodium on salts of the protoxide; and corrosive sublimate or bichloride, HgCl₂, which is formed when hydrochloric acid acts on the peroxide, 2 HCl + HgO₂ = 2 HO + HgCl₂. It is a crystalline heavy substance, soluble in water, and very poisonous. The chlorides are also formed by subliming a mixture of sulphate of peroxide with common salt, which gives a sublimate of bichloride, and, if metallic mercury be added, calomel. Both are volatile, and calomel, whichever way prepared, always contains at first some bichloride. To render it fit for medical use, this must be removed by repeated boiling with water, as long as potash causes a yellow precipitate in the filtered liquid. Both chlorides are much used in medicine, calomel being the milder, and corrosive sublimate the more active of the two.
There are two bromides and two iodides, corresponding to the two chlorides. The iodides are formed by the action of iodide of potassium on the salts of the two oxides. The protiodide, HgI, is of a dirty yellowish green, insoluble, and is resolved by light into periodide and metal, 2 HgI = HgI₂ + Hg. The periodide is of a beautiful scarlet, and insoluble, or nearly so. A moderate heat renders it lemon-yellow, and the yellow form is instantly reconverted into the red by friction, or by the touch of a hard point. In the latter case, the part touched becomes red, and the red colour spreads from it through the mass. The change of colour is owing to a change of position in the molecules, or a change of crystalline form. Both iodides are used in medicine, and the periodide also as a pigment.
Mercury rubbed with 1 eq. sulphur, forms a black powder called ethiose mineral, which is a mixture of the metal with the bisulphuret. With 2 eqs. of sulphur it forms the bisulphuret, which is also produced by the action of hydrosulphuric acid on salts of the peroxide. It is black when thus prepared; but if sublimed becomes dark red, and when finely powdered this acquires the colour of vermilion, which is a form of the bisulphuret.
The compounds of mercury with other metals are called amalgams. They are sometimes liquid, often semisolid. Amalgam of silver occurs native in crystals. Amalgam of tin is used for silvering the backs of mirrors, and an amalgam of tin and zinc for rubbing the cushion of electrical machines.
GROUP VIII.
The Noble Metals.
The metals of this group are so called, because, from their small attraction for oxygen, they do not tarnish in the air, nor even in the fire. Hence their use for ornamental purposes, and for coinage. They are eight in number, namely, silver, gold, platinum, and five rarer metals associated with platinum.
54. Silver.
Symbol Ag (Argentum). Equivalent = 108.
This beautiful metal is found native; also combined with sulphur, arsenic, and antimony, with tellurium, and with chlorine. It occurs also frequently in small but available quantity in galena or lead ore. Native silver, when disseminated in the rock, is extracted by amalgamation with mercury.
Silver has a pure white colour and brilliant lustre. Its specific gravity is about 10,500. It melts at a strong red or white heat, and is quite unaltered in the fire. By the intense heat of the galvanic battery it is volatilized. It is very malleable and ductile, and has considerable tenacity. It is rather soft, and therefore copper is added to form standard silver, which is hard, and wears better. Spanish dollars consist of pure silver, with only a trace of gold, which is present more or less in all silver.
Silver appears to form three oxides; a suboxide, Ag₂O, little known; the protoxide, AgO, a strong base, and a deutoxide or peroxide, AgO₂. The protoxide alone is of interest. It is obtained by adding potash to nitrate of silver, as a brown hydrate, which, when gently heated, loses water, and leaves the protoxide as an olive-coloured powder. Its salts are recognised by the brown precipitate produced by potash, which like nearly all compounds of silver dissolves in ammonia, by the curdy white chloride produced by hydrochloric acid or soluble chlorides, and by the black sulphuret thrown down by hydrosulphuric acid. The metal is reduced by copper, zinc, and iron, and even by mercury.
There is only one chloride, AgCl, which appears as a curdy white substance, insoluble in water and acids, soluble in ammonia, when hydrochloric acid or chloride of sodium is added to the salts of silver. It is fusible, and on cooling forms a semitransparent mass, called horn silver. It is blackened by light, a character common to all the compounds of silver, especially the chloride, iodide, bromide, &c.; on this property is founded the daguerreotype. The chloride, moistened with diluted acid, is reduced by zinc or iron; or it may be boiled with potash and sugar, or ignited to whiteness with lime and a little charcoal, when a button of silver is obtained.
The bromide and iodide resemble the chloride, but the iodide is yellowish and sparingly soluble in ammonia. The sulphuret is black. It is found in nature both pure Chemistry, and combined with arseniuret and antimoniuuret of silver, also in galena with sulphuret of lead.
The chief uses of silver are for coining and for plate. Nitrate of silver is used as a caustic and also internally; and the chloride, iodide, and bromide, are the substances used in photography in the form of a film on the surface of silver, paper, or other substances.
The compounds of silver possess the remarkable property of dissolving in hyposulphite of soda, even when insoluble in water and acids, and this property is made use of in photography to fix the images by removing the unaltered chloride, &c., of silver.
55. Gold.
Symbol Au (Aurum). Equivalent = 99.6.
This metal is found native, as in the gold fields of California, Australia, and others. It is very widely distributed, but often in quantity too small to pay for its extraction. The sand of the Rhine and of most rivers contains traces of it. It is also found combined with tellurium, and alloyed with silver and palladium. Many kinds of pyrites contain gold enough to pay for the working, and it has also been found in galena.
Gold is distinguished by its yellow colour, bright lustre, and great density. Its specific gravity is 19,500. It is the most malleable of all metals, and also highly ductile. It melts in a white heat.
Gold does not combine directly with oxygen, and is dissolved by no single acid, but only by a mixture of nitric and hydrochloric acids, called aqua regia, or nitro-hydrochloric acid. This forms a chloride from which alkalies precipitate the oxide, which is a tetroxide, $\text{Au}_2\text{O}_3$, as a brownish-yellow powder, which loses its oxygen when exposed to a moderate heat. It has weak acid properties, and is sometimes called auric acid. There is a suboxide of a violet colour, little known.
The terchloride of gold, $\text{AuCl}_3$, is by far the most important compound. It is formed, as above stated, by means of aqua regia. It is reduced to the metallic state by protosulphate of iron, by formic acid and formiates, by oxalic acid, and by various metals. With the chlorides of the positive metals terchloride of gold forms crystallizable double chlorides.
The compounds of gold with sulphur are little known. Hydrosulphuric appears to form, in solution of the terchloride, a bisulphuret, which is black.
56. Platinum.
Symbol Pt. Equivalent = 98.7.
This metal is also found native, but combined or mixed with five other metals, namely iridium, rhodium, palladium, ruthenium, and osmium, all of which occur in very small quantity in the native platinum which is found in grains. Aqua regia dissolves the whole, except the black scales of an alloy of iridium and osmium, and a few particles of iridium. The solution is mixed with sal-ammoniac, and the bichloride of platinum which has been formed combines with that salt, chloride of ammonium, to form a nearly insoluble double chloride, $\text{PtCl}_4\text{NH}_4\text{Cl}$, which is deposited as a bright yellow powder. If much iridium be present, the salt is coloured reddish from the presence of the corresponding double chloride of iridium. The washed salt is dried and ignited, when it leaves spongy platinum. By repeating the process the iridium is got rid of in the mother liquid. The spongy metal is made into a paste with water in a wooden mortar, and this paste gradually but powerfully compressed till it assumes a metallic aspect. It is then heated red-hot and hammered gently, and this is repeated till it becomes of full density. It has a greyish-white colour, a high lustre, and a specific gravity of 21,500.
It forms two oxides, a protoxide and a deutoxide, which are feeble bases, and little studied. Its most important Chemistry compound is the bichloride, $\text{PtCl}_4$. This, with the chlorides of the positive metals, forms crystallizable and permanent double chlorides. Those of potassium and ammonium are nearly insoluble, and the latter, as above stated, yields pure spongy platinum when heated. That of sodium is soluble even in alcohol, and forms fine large crystals. In consequence of this property bichloride of platinum is used to absorb the ammonia formed from the nitrogen of organic compounds, and thus to determine the quantity of that nitrogen.
When the bichloride, which is an orange-coloured soluble salt, is heated to a certain point, it loses half its chlorine, and leaves a protochloride, as a green powder, insoluble in water, but soluble in hydrochloric acid. This chloride also forms double chlorides with the chlorides of the positive metals. With ammonia it gives rise to a remarkable series of bases containing platinum, nitrogen, hydrogen, and in some cases chlorine. These resemble organic bases.
The other metals found along with platinum are extracted from the mother liquid after the precipitation of the platinum by sal-ammoniac, by a very tedious and complex series of operations. Iridium and osmium are also obtained from an alloy of these metals left undissolved by the acid. They all resemble platinum, iridium the most, then rhodium, ruthenium, palladium, and osmium. Their chlorides are the chief compounds, except in the case of osmium, which forms with oxygen a remarkable crystallized and volatile acid, osmic acid, $\text{Os}_2\text{O}_4$. These chlorides form double chlorides with potassium, ammonium, sodium, &c., analogous to those of platinum. The salts of rhodium are rose-coloured, those of iridium of various colours, those of palladium brown, and those of ruthenium reddish. All these metals are very infusible, and unaltered in the fire, like platinum. But they are so scarce, except palladium, which is malleable, and is used by dentists instead of gold, that they can hardly be applied to useful purposes. Iridium, or rather an alloy of it with a little platinum, as found in the ore, in small grains, is used for the points of gold pens, and from its extreme hardness does not perceptibly wear. Iridium is also the heaviest of metals, its specific gravity being 26,000. We shall not enter into further detail in regard to these very scarce metals.
Having concluded this brief notice of the elementary bodies, and of their chief binary compounds, the reader is now acquainted with the fundamental facts of chemistry. There is, however, an important class of compounds which we have only noticed incidentally, namely the salts, and although we cannot describe them in detail, we may offer some general remarks which will facilitate the study of them.
One division of saline compounds has been described in the place they naturally occupy, namely, those salts called haloid salts, formed of a metal united to such bodies as chlorine, bromine, &c. These, in fact, are true typical salts, for the very substance from which the name of the class is taken, common or sea salt, is one of them, being the chloride of sodium. In one sense, every body having similar properties may be called a salt; every body which is crystalline, more or less soluble, rapid, and neutral. Accordingly at an early period the term salt was extended to such bodies in general, and even after the true nature of common salt was known (for it had long been viewed as a compound of hydrochloric acid and soda) those bodies which really consisted of an acid and a base, both generally oxidized, such as sulphate of soda, nitrate of potash, and the like, were still regarded as salts, and even considered as the only true salts, on the theory that a true salt was a neutral compound of an acid and a base. This theory, in the end, actually excluded common salt from the class of salts; and therefore two kinds of salts were admitted; oxygen salts, of which sulphate of soda, $\text{Na}_2\text{SO}_4$, is a type; and haloid salts, of which common salt, $\text{NaCl}$, is the Chemistry. We have already shown how, by the progress of chemical discovery, we have been enabled to reduce to one series the two classes of acids, namely, oxygen acids, such as sulphuric acid, HO, SO₄, and hydrogen acids, such as hydrochloric acid, HCl. This is done by regarding the hydrogen in the former as being combined, not first with oxygen to form water, and the water with the dry acid, but as united with a radical, SO₄, differing from chlorine only in being certainly compound. Although this particular radical, SO₄, be not yet known in a separate form, many such compound radicals are known, and play exactly the part of chlorine. Of these cyanogen, C₂N=Cy, is the type. On this view, therefore, while hydrochloric acid can only be HCl, sulphuric acid, represented as H₂SO₄, or more simply, making SO₄=Su, by HSu, becomes as perfectly analogous to it in formula as it is in properties.
Now, if we adopt this view of acids, or at least all such acids as cannot exist in an active state without hydrogen, formerly supposed to be present as water, we must apply the same view to the salts of those acids. For when hydrochloric acid acts on a base, such as soda, two phenomena are constantly observed—the formation of a neutral salt and the separation of water. This is perfectly obvious from the equation (M representing any metal), HCl+MO=MCl+HO. But when sulphuric acid acts on the same bases the phenomena are absolutely the same; a neutral salt is formed, and water separated. And this we express by the equation, H₂SO₄+MO=M₂SO₄+HO.
Here, then, we see the first great principle to be admitted concerning salts. They represent hydrogen acids, in which the hydrogen is replaced by a metal, and therefore acids (that is, hydrogen acids, which includes what used to be called hydrated acids) and salts form in reality but one series, the general formula of which is XR; R being any negative acid radical or salt radical, for the terms are synonymous, and X standing for the positive element, which may be either hydrogen or a metal. So that acids, in this view, are salts of hydrogen, and salts are salts of metals. Hydrogen, indeed, is possibly or even probably the gas of a very volatile metal, whose salts are peculiar in this, that they possess those characters which we call acid. The analogy between neutral salts and acids, nay, even between neutral salts, acids, and bases, or alkalies, did not escape the first scientific chemists, although they knew nothing of the true constitution of any of them. In all works published towards the end of the last century, acids, alkalies, and neutral salts are all included under the head of saline substances. This view, founded on acute observation, was for a time displaced by the limited notion of a salt being a compound of an acid and an alkali, which, as we have seen, actually excluded common salt from the class of salts, as soon as it was shown to contain neither oxygen nor hydrogen, and consequently not to be, as was supposed, a compound of hydrochloric acid with soda. But the progress of science has shown that as oxygen can no longer be called the acidifying principle, since hydrogen is better entitled to the name, so all acids, bases, and salts really belong to one series, that represented by XR. Water may be taken as the type of all such compounds, and while its oxygen may be replaced by chlorine, bromine, iodine, fluorine, sulphur, selenium, cyanogen, the radicals, SO₄ (in sulphuric acid), NO₃ (in nitric acid), &c., &c., its hydrogen may be replaced by any metal, or by such compound radicals as can play the part of metals, as cyanogen and SO₄ play that of chlorine. In organic chemistry there are, as we shall see, many such radicals, of which ethyle, C₂H₅=AE, is a good example.
Such being the nature of salts in general, it is easy to see how neutral salts are formed when acids and bases act on each other. They were formerly supposed to combine directly, but we now know that if the acid be a hydrogen acid, or a hydrated acid, and the base an oxide, this is not Chemistry, the case, but that water is always formed, as in the general equation, HR+MO=MR+HO. We have just stated how this applies to sulphuric acid, HO, SO₄, or rather, H₂SO₄. But when anhydrous sulphuric acid acts on an anhydrous base, the reaction is different; no hydrogen being present, no water can be formed, but yet the same neutral salt is formed, as, to take the case of sulphuric acid and soda, both anhydrous, in the equation, NaO+SO₄=Na₂SO₄. Here, instead of simply uniting together, the acid and base react on each other; the oxygen of the base is transferred to the acid, producing the radical, SO₄, and with this the metal unites.
The salts of ammonia come into the same category as those of metallic protoxides. For, as has been already explained, in every salt of ammonia, NH₄, with an oxygen acid, there is found, besides the ammonia and anhydrous acid, invariably 1 eq. of water, HO, or rather its elements. The salt, NH₄, SO₄, if it exist at all, is not sulphate of ammonia. That salt contains the elements, NH₄, HO, SO₄, which, on the old view, are arranged as NH₄O, SO₄, sulphate of oxide of ammonium, and on the new as NH₄, SO₄, or, making ammonium, NH₄=Am, it is written Am, SO₄, perfectly corresponding to K, SO₄, sulphate of potash, which it resembles very closely in properties. When ammonia, NH₄, acts on hydrogen acids, such as hydrochloric acid, it was formerly supposed to combine directly with the acid, and the resulting salt, sal-ammoniac or hydrochlorate of ammonia, was written NH₄, HCl. It is now believed that here also ammonium is formed by the hydrogen of the acid combining with the ammonia, and that the compound metal thus formed combines with the residual chlorine, just as potassium would do; so that the result is NH₄+HCl=NH₄Cl=Am Cl, and the salt is now called, accordingly, chloride of ammonium, being perfectly analogous in all respects to chloride of potassium or sodium. In other words, as cyanogen or SO₄ may replace the oxygen of water or the chlorine of sea-salt, so ethyle, C₂H₅=AE, and ammonium, NH₄=Am, can replace the hydrogen in water and the metal in salt, being, in fact, compound metals.
On the views above explained, neutral salts become exceedingly simple, and the law of their formation very easily remembered, while water, acids, and bases all fall into the same category.
Besides neutral salts, there are acid or supersalts, and alkaline or subsalts. The former, in the case of such acids as sulphuric acid, may be regarded as compounds of the acid with a neutral salt. Thus acid sulphate, or bisulphate of potash is KO, HO, 2 SO₄=K, SO₄+H, SO₄=HJ, SO₄. The latter are compounds of the neutral salt with an additional quantity of the base, as, for example, subnitrate or basic nitrate of lead, which is 2 PbO, HO, NO₃=Pb O, NO₃+Pb O, HO=Pb, NO₃+Pb O, HO.
There is, however, another kind of acid salts, namely, those of polybasic acids. Of such acids, phosphoric acid is an excellent type, in two of its three modifications, the dibasic and tribasic phosphoric acids. Polybasic acids, especially dibasic ones, are very frequent in organic chemistry. Of the organic dibasic acids, oxalic acid is the type.
A dibasic acid is one which, to form a neutral salt, requires 2 eqs. of base. Dibasic phosphoric acid is PO₄, 2 HO, or rather H₃, PO₄, the 2 eqs. of hydrogen being replaceable by metals. The neutral dibasic phosphate of silver is Ag₂, PO₄. But if only 1 eq. of hydrogen be replaced by a metal, we have the acid only half neutralized, or an acid salt, as the acid dibasic phosphate of silver, which would be Ag₁, PO₄, or that of potash, which is K₁, PO₄.
The same is true of tribasic acids, which form three series of salts with the same base, according as 1, 2, or 3 eqs. of Chemistry. Hydrogen are replaced by the metal. Tribasic phosphoric acid is $\text{PO}_4$, $3\ \text{HO} = \text{H}_3\ \text{PO}_4$; and it forms with soda, three salts, namely, the acid salt $\text{Na}_2\ \text{H}\ \text{PO}_4$, the acid salt $\text{Na}_2\ \text{H}\ \text{PO}_4$, and the neutral salt $\text{Na}_2\ \text{PO}_4$. The two latter are alkaline in reaction on test paper, although acid and neutral in composition; but, in fact, all three, as well as the two salts of the dibasic acid, are strictly speaking, neutral salts in composition, since they all contain the same number, whether two or three, according to the acid, of basic equivalent, whether metal or hydrogen. Accordingly, all the three salts of soda with the tribasic acid, form, with salts of silver, the same yellow precipitate of neutral tribasic phosphate of silver, $\text{Ag}_3\ \text{PO}_4$. Oxalic acid is $\text{C}_2\ \text{O}_4$, $2\ \text{HO} = \text{H}_2\ \text{C}_2\ \text{O}_4$, and it forms a neutral oxalate of potash, $\text{K}_2\ \text{C}_2\ \text{O}_4$; an acid oxalate of potash called binoxalate, $\text{K}_2\ \text{C}_2\ \text{O}_4$, and a double acid oxalate of potash, called quadroxalate, $\text{K}_2\ \text{C}_2\ \text{O}_4 + \text{H}_2\ \text{C}_2\ \text{O}_4$.
With regard to salts considered individually, they may be studied either under the head of all the salts of one acid radical with different bases, or all those of one base with different acid radicals. On the former plan they are arranged as sulphates, nitrates, phosphates, chlorides, bromides, &c.; on the other as the salts of potassium, sodium, ammonium, iron, lead, silver, &c. There are conveniences belonging to both systems, but our space will not permit us to enter into either. We can only point out that all the salts of one radical, all the sulphates, or all the chlorides exhibit the characters of that radical. Thus all the soluble sulphates form an insoluble precipitate of sulphate of baryta when mixed with salts of that base. All the chlorides are Chemistry, in like manner precipitated by salts of silver. All the nitrates delagrate with red-hot charcoal, &c. Nor are we confined to one character; for all the sulphates, for example, when ignited with charcoal, yield sulphurets, and the smell of hydrosulphuric acid is perceived when acids are added to the ignited mass. This is because they all contain sulphur.
Again, all the salts of one metal or base exhibit the chemical characters of that metal. Thus all the salts of sesquioxide of iron give Prussian blue with ferrocyanide of potassium. All the salts of silver give the insoluble chloride on the addition of hydrochloric acid or solution of salt.
Now, as we have in all cases given the characters by which acids and radials, metals and bases, may be recognised, the chemical characters of any salt may be known by referring to those of its elements. We may merely state here that the most valuable and important salts, most of which have been noticed incidentally under the head of their acids or their bases, are the sulphates, especially those of lime, magnesia, baryta, soda, potash, alumina and potash, iron, zinc, copper, and ammonia; the nitrates of potash, soda, strontia, lead, mercury, and silver; the carbonates of lime, magnesia, potash, soda, ammonia, iron, zinc, lead, &c.; the phosphates of soda, potash, lime, of magnesia and ammonia; the chlorate of potash, the chromates of potash and of lead; and many salts of organic acids not yet described, as oxalates of lime and of ammonia, acetates of potash, soda, alumina, iron, zinc, and lead; and tartrates of potash, potash and soda, and potash and antimony. The haloid salts, such as chloride of sodium, iodide of potassium, fluoride of calcium, &c., have been described in their proper place.
ORGANIC CHEMISTRY.
We must now turn to the chemistry of organized bodies, animal and vegetable, and of the unorganized or structureless products of animal or vegetable life; both of which classes of compounds are called organic.
As formerly explained, the elements of organic bodies are the same as those which constitute the inorganic world, save that the relative proportions are different, and that few comparatively of the elements can enter into the composition of organic compounds. The chief mass of such compounds is formed of only four elements, carbon, hydrogen, nitrogen, and oxygen; frequently of carbon, hydrogen, and oxygen alone; sometimes of carbon and hydrogen only. In every case of an organized structure, however, or of any substance capable of being formed into such a structure or tissue, there are not only the four elements just mentioned, but also sulphur, and several mineral salts in small proportion, but equally essential with the rest. These salts are phosphates, chlorides, alkalies, probably introduced as carbonates, oxide of iron, and frequently iodides and fluorides. Where these saline matters are absent—that is, where the substance, on being burned, leaves no ashes—it is invariably destitute of organized structure, and frequently either crystallized or liquid, both these forms being incompatible with organization.
Organic substances then are characterized by the small number of their elements, and, since they are themselves exceedingly numerous, by the great variety of proportions in which the same elements are united. By far the greater number of organic compounds are only products of organic life, and not themselves organized; and these consist either of the four elements which may be called organic, carbon, hydrogen, nitrogen, and oxygen, or of carbon, hydrogen, and oxygen, without mineral matter or ashes. Such compounds are the vegetable acids, sugar, gum, oils and fats, the vegetable bases, colouring matters, resins, and the like, in plants, and in animals such compounds as fats and oils, bile, urea, animal acids, and bases, &c. To these must be added the innumerable compounds derived from them by various chemical processes. The few organized tissues, and the substances of which these may be formed, are such bodies as bone, muscle, nerve, membranes, woody tissue, albumen, fibrine, casein, gelatine, chondrine, and the like.
Now, all such organic substances, organized or not, agree in containing a large amount of carbon; and as this is combined with the elements we have named, oxygen, hydrogen, nitrogen, and in some cases sulphur, the action of heat on them, with or without the access of air, is peculiarly characteristic, and enables us at once to recognize organic compounds. Heated in close vessels, they blacken, give off water, oily matter, and combustible gases, and leave behind a black mass, composed of carbon and ashes, if there be ashes present. Heated in the open air, they are oxidized, the whole of their hydrogen being given off as water, their carbon as carbuncle acid, their nitrogen as ammonia or as nitrogen gas, while the ashes alone remain. In the first case, which is called the destructive distillation of organic matter, the oxygen present is chiefly taken up by hydrogen to form water, while the carbon enters into new combinations with hydrogen and oxygen, or with hydrogen alone, or with nitrogen; and as all the compounds thus formed are gaseous, the carbon is carried off, as far as the quantity of the other elements admits of, but a large part is always left as charcoal, for want of other elements to combine with it. All organic bodies, therefore, are charred by heating when air is excluded, as in a retort or in the bottom of a tube, and burn when heated with a full supply of air. These characters depend on the nature of the elements they contain, and above all, on the presence of so large a proportion of carbon.
Organic bodies differ from the inorganic in their comparatively complex formulas. Thus, in inorganic chemistry we constantly meet with such formulas as those of water, HO, hydrochloric acid HCl, potash KO, sulphuric acid SO$_2$ or HO, SO$_3$, and the like. But the simplest organic Chemistry, compounds are more complex than this. Formic acid is \( \text{C}_2\text{H}_4\text{O}_2 \), oxalic acid \( \text{C}_2\text{H}_4\text{O}_4 \), acetic acid \( \text{C}_2\text{H}_4\text{O}_2 \), and these are by far the simplest organic compounds. Benzoic acid is \( \text{C}_6\text{H}_5\text{O}_2 \), urea is \( \text{C}_2\text{H}_4\text{N}_2\text{O}_2 \), sugar is \( \text{C}_{12}\text{H}_{22}\text{O}_{11} \), quinine is \( \text{C}_{20}\text{H}_{24}\text{NO}_3 \); and while many organic compounds are equally or more complex, some of them, especially those which are capable of forming blood and tissues, contain hundreds of atoms in a single molecule. This peculiar complexity of constitution, while but a small number of elements are employed, is a very marked character of organic compounds, and one consequence of it is, that they are much more easily decomposed by heat or by chemical means than inorganic substances, while the products of their decomposition are singularly varied. In fact, when so many atoms are present, and the elements are capable of uniting two and two or three together, in an endless variety of proportions less complex than the compound acted on, the results may be modified almost ad infinitum by altering the circumstances, such as temperature, or the reagents employed, which may be oxygen, or different oxidizing agencies of various energy, or acids, or bases, or chlorine, or any two or more combined, or any of the various modes of deoxidation, or of removing hydrogen, and so on; when such are the conditions, it is easy to see that the results must be infinitely more varied than they can possibly be in the case of inorganic compounds, the composition of which is in general so little complicated. This capability of undergoing numerous decompositions or transformations under the influence of the known chemical agencies is another characteristic feature of organic compounds; and there are causes of change which are almost peculiar to organic substances, such as the action of what are called ferments, and the power we have of replacing one or more atoms of one of the elements of such compounds, generally the hydrogen, by its equivalent of other elements, or even of compound radicals, or groups acting the part of elements. We may say, then, that organic compounds are complex in their constitution, and in consequence peculiarly liable to transformations and decompositions of various kinds—a character which renders them eminently fitted for the functions they have to perform in plants and animals. And while this is true of organic compounds generally, it is especially true, as was formerly hinted, of those which contain nitrogen, from the fact that that element has nearly equal affinities for the three elements which accompany it, and a great tendency also to combine with two or with all three of them in various proportions. Those organic bodies, and they are numerous, which undergo spontaneous transformations, are always compounds containing nitrogen.
Another peculiarity of organic compounds is this, that all their chief elements are either gaseous in themselves, or have a strong tendency to form gaseous or volatile compounds; so that the ultimate result of the transformations of the most complex of them, aided by the atmosphere, is their entire conversion (the ashes alone excepted) into the least complex gaseous forms; and they are sent into the air in those forms, which are, carbonic acid, \( \text{CO}_2 \); water, \( \text{HO} \); ammonia, \( \text{NH}_3 \); hydrosulphuric acid gas, \( \text{HS} \); and sulphuric acid, \( \text{HO}_2\text{SO}_4 \). The decay of a dead animal or of a dead tree produces these very substances; and the whole mass of both, excepting the ashes, is dissipated in these forms, chiefly by the action of the atmospheric oxygen, aided by their own tendency to change. In this way, not only is the accumulation of dead organic matter prevented, but its disappearance is, as we shall see, the regular and unfailing source of food to the new generation of plants, and to the animals which feed on them. There are no elements known to us which are capable of undergoing these successive changes, except those which we find in organic matter.
Such are the characters which distinguish organic from inorganic compounds; and it will be seen that, while in both classes the same laws of combination prevail, the peculiarities of the former depend on the peculiar nature of their principal elements.
The number of natural organic compounds is so great, and that of the compounds derived from them artificially is so much greater, that we cannot pretend to describe them all. We can only state such general laws as are deducible from what is known, and indicate the groups or series into which organic substances naturally fall. We shall find that they have a peculiar tendency to form groups of analogous constitution and properties, and that these groups exhibit a repetition, on a larger scale, of what we have already seen among elementary bodies. There are, no doubt, many organic compounds which as yet appear to stand alone; and this renders a satisfactory classification for the present unattainable. But this is entirely due to the imperfection of our knowledge, and the rapid daily progress of organic chemistry is constantly opening up new views, which enable us to include in the known series more and more compounds every day. This progress also demonstrates that the natural groups of organic compounds are formed on the same principles as those of inorganic substances; that the types, so to speak, are the same, while the differences do not affect essential or fundamental points, and the general analogy is unmistakeable.
**COMPOUND ORGANIC RADICALS.**
Organic chemistry has been defined as the chemistry of compound radicals, as opposed to inorganic chemistry—that of elementary or simple radicals. But since we have come to admit in the latter such compound radicals as \( \text{SO}_4 \) in sulphuric acid and sulphates, \( \text{NO}_3 \) in nitric acid and nitrates, and many others, this definition cannot be maintained. We might say, indeed, that organic chemistry was that of such compound radicals as contain carbon. It is probable that all organic compounds contain at least one such radical (except in the case of ammonia and its derivatives, amide and ammonium, if considered organic), and that this is the cause of their complexity.
A compound organic radical is a group which plays the part of an element, and enters as a whole into combination with either elements or other compound radicals. Only a few of the organic radicals admitted by chemists are known in the separate state, but some are known with certainty; and where this is not the case, yet the assumption of the existence of such a radical often simplifies, in an extraordinary degree, the understanding of a whole series of connected substances, and reduces them to a form as easily remembered as in the case of a metal or a negative radical, such as chlorine.
Among organic radicals we find the same diversity of character as among elementary bodies. Some are negative, resembling chlorine, &c., in their relations; others positive, resembling hydrogen or metals; some, again, are more analogous to combustible bodies like carbon and sulphur; and some cannot be referred exactly to any of these categories, but partake of more than one. These differences of negative and positive, however, are, as the reader knows, differences of degree; so that all radicals, compound as well as simple, may be arranged in a series, in which each is positive to the next on one side, and negative to the next on the other. Among the elements this is well known; of the organic radicals, too few are yet known to enable us to establish such a series, save in a very fragmentary manner.
Of strongly negative organic radicals, analogous to chlorine, cyanogen is the type, and the analogy is here truly surprising. Thus we have—
| With Chlorine, Cl | With Cyanogen, C, N = Cy | |------------------|------------------------| | Hydrochloric acid, HCl | Hydrocyanic acid, HCy | | Hypochlorous acid, ClO | Cyanic acid, CyO | | Chloride of potassium, KCl | Cyanide of potassium, KCy | | Bichloride of mercury, HgCl₂ | Bicyanide of mercury, HgCy₂ | Chemistry. There are other negative radicals, chiefly derived from cyanogen, such as ferrocyanogen, C₄N₄Fe = Cy₄Fe = Cl₄Cy, sulphocyanogen, C₄NS₂ = CyS₂ = Cy₄, and various others, which exhibit a general resemblance to chlorine in their relations, forming acids with hydrogen and salts with metals.
Of such positive radicals as are analogous to hydrogen and metals, and can, indeed, replace them, the simplest and the type is methyle, C₄H₄ = Me. Let us compare it with potassium. We have—
| With Potassium, K | With Methyle, C₄H₄ = Me | |-------------------|------------------------| | Protioxide, basic, KO | Protioxide, basic, MeO | | Hydrated protioxide, KO, HO | Hydrated protoxide, MeO, HO | | Chloride, KCl | Chloride, MeCl | | Iodide, KI | Iodide, MeI | | Sulphuret, KS | Sulphuret, MeS | | Cyanide, KCy | Cyanide, MeCy | | Nitrate, KNO₃ | Nitrate, MeNO₃ | | Carbonate, KO₃CO₃ | Carbonate, MeO₃CO₃ | | Acetate, KO₃C₂H₅O₂ | Acetate, MeO₃C₂H₅O₂ |
This list might be extended to a great length, and the analogy would hold good. It is easy to see how much the assumption of the radical methyle simplifies its compounds, the formulae of which, written at full length, no one could be expected to remember, many of them being very like each other. Thus the carbonate is C₄H₄O₃; the cyanide, C₄H₄N; the hydrated oxide, C₄H₄O₂; and the acetate, C₄H₄O₂.
There are very many radicals of this class, and all more complex than methyle, but all equally simple when considered as radicals, each having its own symbol. Thus, we have ethyle, C₄H₄ = Ae; amyle, C₁₀H₁₆ = Ayl; cetyl, C₁₈H₃₆ = Ct; phenyle, C₁₂H₁₄ = Ph; and many others.
Of the radicals analogous to sulphur or carbon, benzoyle is a type. Its formula is C₆H₅O₂; its symbol Bz; and we have it, as well as sulphur, in combination with—
| Sulphur. | Benzoyle. | |----------|-----------| | Hydrogen | H₂ | | Oxygen | SO₂, HO | | Chlorine | Cl₂ |
The analogy is not so close here as in the other cases, but the principle is the same. There are a good many radicals of this type, all forming with hydrogen volatile oils, with oxygen volatile acids. Acetylene, C₂H₂ or rather formylic, C₂H₂ is the type of another allied group of radicals, which form with hydrogen volatile oily products, and with oxygen volatile acids of an oily character.
Such are the general characters of some of the best known groups of organic radicals, and it is precisely the compounds connected with these which are best known, and the study of which is most simplified by the admission of these radicals.
ISOMERISM IN ORGANIC COMPOUNDS.
Another remarkable feature in organic compounds is the frequent occurrence of isomerism or polymerism. This is the natural result of the large number of atoms generally present, which of course admits of a great variety in their arrangement, giving rise to isomeric compounds; while the absolute number also varies, being double, or treble, or manifold in one compound of what it is in another, thus producing polymeric compounds. It is obvious that in either case the transformation of one compound into the other must be comparatively easy, since nothing is necessary to be added nor taken away.
As examples of isomerism, that is, of bodies with the same proportion of elements and the same absolute quantity, which makes the atomic weight or equivalent the same, we may mention cyanate of ammonia (of oxide of ammonium), and urea. The former is AmO₃CyO = NH₄O₃C₄NO₃, and the latter the rational formula is not known with certainty, but the empirical formula is C₄H₄N₂O₃, which, it will be seen, is the same, absolutely and relatively, as the other. Again, acetate of oxide of ethyle is AcO₃AcO = C₄H₄O₃C₄H₄O₃ = C₄H₄O₄, while butyric acid is C₄H₇O₂HO = C₄H₄O₄.
These two substances are totally different, and we are able to express the difference in the rational formula, which shows the first to be a neutral salt of oxide of ethyle, the second a hydrated acid. A still more striking case of isomerism is that of the following substances, in several of which the rational formula is unknown, but all of which have the same atomic weight, and entirely different properties:
| Substance | Empirical Formula | Rational Formula | |-----------|------------------|-----------------| | Alanine | C₄H₇NO₂ | C₄H₇NO₂ | | Sarcoine | C₄H₇NO₂ | C₄H₇NO₂ | | Carbamate of oxide of ethyle | C₄H₇NO₂ | C₄H₇NO₂ | | Hypotrioxide of propyle | C₄H₇NO₂ | C₄H₇NO₂ |
Here we have at all events three totally distinct rational formulas, and in regard to the two first substances it is not that they have the same rational formula, but that we do not yet know the difference, which, as both seem to be hydrated bases but of distinct properties, must of course be in the arrangement of the anhydrous base C₄H₇NO₂. There must be a difference, and we might even from analogy conjecture several modes of explaining the difference of properties, but nothing is certainly known of it. It is quite probable that several more substances having the same composition and atomic weight may still be added to this list. These examples of strict isomerism will suffice. As to polymerism, we have an example of it, connected with the four substances just mentioned; for lactamide, a body quite different from all four, has the empirical formula C₄H₁₁N₂O₃, exactly double of theirs. Its rational formula is probably C₄H₁₁N₂O₃, 2NH₃, which represents the neutral amide of lactic acid, a bisbasic acid. We have also an example of polymerism, connected with acetic ether and butyric acid, the empirical formula of which is C₄H₉O₂. That of aldehyde is C₄H₅O, or exactly one-half, while its rational formula is C₄H₅O, HO, that is, hydrated protoxide of acetylene. Besides this, we have metaldehyde and cladehyde, polymeric with aldehyde, the precise equivalent of which is doubtful. There are also the three acids, formed of cyanogen and oxygen, namely—
| Cyanic acid | CyO₃HO | C₄NO₃HO | | Fulminic acid | Cy₃O₃₂HO | C₄N₃O₃₂HO | | Cyanuric acid | Cy₃O₃₃HO | C₄N₃O₃₃HO |
Many other examples might be given, both of isomerism and of polymerism; but those already given are sufficient to illustrate the principle. There is, indeed, a remarkable class of compounds, namely, the volatile bases, homologous with ammonia, and in which the hydrogen of that substance is partially or entirely replaced by radicals of the ethyle series, which exhibit isomerism carried to an extraordinary point, as will be more particularly explained under the head of these bases. Suffice it here to say, that we may easily form two volatile bases similar in properties, but quite distinct, of the formula C₄H₄N; three such bases of the formula C₄H₄N; four of the formula C₄H₄N; six of C₄H₄N; and so on, the number regularly increasing with the amount of carbon, so that with 20 eqs. of carbon we may have 16 volatile bases, all of the same empirical formula C₄H₄N, and yet all distinct, and each having its own well ascertained rational formula. Nor does this stop here, for with every 2 eqs. of carbon by which the formula is augmented, the number of possible isomeric (not polymeric) volatile bases is increased by two. This will give the reader some notion of the extraordinary fertility of organic chemistry, and of the important part performed by isomerism in the transformation of organic compounds. It is but the other day that these volatile bases were discovered, and already some dozens of them are known.
The examples of isomeric and polymeric transformation are very numerous, and there can be no doubt that this is a principle constantly in action in living organisms, animal or vegetable. The artificial formation of urea is a striking instance. The cyanate of oxide of ammonium, which we Chemistry have just seen to be isomeric with urea, spontaneously changes into that substance when its solution is left to itself, and rapidly if warmed. Urea, when heated, is transformed or resolved into ammonia, and hydrated cyanuric acid, polymeric with cyanic acid. That is to say, 3 eqs. of urea yield three of ammonia and 1 of cyanuric acid, $C_3H_4N_2O_3 = 3NH_3 + Cy_3O_3$, 3 HO. Again, this very cyanuric acid, when heated, is resolved into 3 eqs. of cyanic acid, $Cy_3O_3$, 3 HO = 3 (CyO, HO). Cyanic acid, left to itself, is transformed into cyanamide, a body polymeric with it, possibly having twice its equivalent, $2(CyO, HO) = C_4H_2N_2O_4$. Cyanamide, when heated, is resolved, like cyanuric acid, into cyanic acid again, $C_4H_2N_2O_4 = 2(CyO, HO)$. If we now add ammonia, we obtain cyanate of oxide of ammonium, and this can be made again to pass through the whole series of metamorphoses just mentioned. Hydrobenzamide, by boiling with potash, is transformed into the base amarine, isomeric or perhaps polymeric with it. Furfuramide, in the same way, is transformed into the base furfurene, which has exactly double its equivalent. Every case of fermentation, strictly so called, is one of isomeric or polymeric transmutation; not, however, generally into one, but into two or more compounds. Dry grape sugar $C_{12}H_{22}O_{11}$ yields, in the vinous fermentation, 2 eqs. of alcohol and 4 of carbonic acid, $C_{12}H_{22}O_{11} = 2(C_2H_5O_2) + 4CO_2$. The same substance, in the lactic fermentation, yields the isomeric lactic acid, $C_{12}H_{22}O_{11} = C_3H_6O_3 + 2HO$. Lactic acid, in the butyric fermentation, is resolved into butyric acid, carbonic acid, and hydrogen, $C_3H_6O_3 + 2HO = C_4H_8O_2 + HO + 4CO_2 + H_2$. It is easy to see how very important a principle this is, in reference to the vital changes which constitute organic life, animal or vegetable. It is in some such way that the food of plants and animals is assimilated, and becomes converted into those substances of which the animal and vegetable frames are composed. It is more particularly in the animal body, however, that isomeric transformations prevail, because the food of animals is complex, and therefore liable to transformation, and adapted to undergo it. We can even, in some measure, imitate artificially the change by which some parts of the food of animals are dissolved into blood. For we can so treat fibrine as to obtain from it a solution of albumen, much resembling the serum of blood; and albumen is either isomeric with fibrine or very nearly so.
ORGANIC TYPES. SUBSTITUTION.
We have seen that great advantage is gained by admitting the existence of organic compound radicals. There is, however, another kind of organic group, which has not the properties of radicals. These are named types, the meaning of which is, that the atoms are grouped together in a certain mode, on which the properties of the compound so entirely depend, that, provided this grouping or arrangement be retained, great changes may be made in regard to the individual elements, without changing the general character of the compound. This leads us to the very remarkable and important law of substitution, which has become so fertile in discoveries of late years. Some writers have imagined that the notion of types was incompatible with that of radicals, but this is not the case. Every radical, nay, every compound of a radical, may also be a type, and we shall find that both ideas are useful in enabling us to classify our knowledge.
The fundamental idea of a type may be found in inorganic chemistry. Hydrochloric acid, HCl, is a type, and so is common salt, NaCl. All compounds, which, like hydrochloric acid, consist of 1 eq. hydrogen and 1 eq. of a powerful negative radical, are acids. All those which consist of 1 eq. of metal and 1 eq. of negative radical, are salts. We can substitute for the chlorine in either, bromine, iodine, cyanogen, or sulphur, and the compound will still have the original character of an acid or a salt. And in the case of salt, we may substitute for the sodium, potassium, ammonium, Chemistry, barium, iron, lead, silver, &c., and still the result is a salt. In fact, every compound is, or represents, a type, and every chemical change is a substitution. But in inorganic chemistry, the only substitutions which do not destroy the type are those of like for like, of chlorine for iodine, &c., or of one metal for another. It cannot well be otherwise, from the simplicity of inorganic formulas.
But in organic chemistry, where the formulae, and consequently the molecules, are so much more complex, the type acquires a new significance. The elements of all organic compounds being the same, and often in the same amount and proportion, the arrangement or relative position of the atoms comes to be a matter of the utmost importance, as fixing the character of the group, that is, of the type. A certain mode of arrangement gives acid properties; another, the properties of a base; a third, those of an oil; a fourth, those of an ether, and so on. And so powerful is the influence of arrangement in these complex molecules, that substitution is no longer confined to replacing like by like, but extends to the replacement of an element by its equivalent of another, not only not analogous to it, but actually opposite to it.
Naphthaline is $C_{10}H_8$. The character of the type is, that it is volatile and combustible. Now, we may remove 1 eq. of hydrogen, and replace it, not by anything analogous to hydrogen, but by 1 eq. of chlorine, forming the body $C_{10}H_7Cl$; chloranaphite, which has the same general characters. We may go on replacing the hydrogen, atom by atom, by chlorine, and yet the type will remain unaltered. That is, the properties of naphthaline depend chiefly on the way in which the atoms are grouped, and, provided the grouping be unchanged, it does not appear to signify much whether the 8 atoms attached to the 20 of carbon be all hydrogen, or partly hydrogen and partly chlorine. In like manner, bromine may be substituted for the hydrogen, and yet we know that, in general, chlorine and bromine are strongly opposed to hydrogen, being negative, while it is positive. Here, then, we have negative atoms playing the part of positive ones, and this is the peculiar feature of that kind of substitution in organic compounds which we are now considering. And since the negative character of such bodies as chlorine and bromine is thus, as it were, sunk, nay, changed almost to its opposite, it is evident that in naphthaline the nature of the compound molecule must depend far more on the arrangement or grouping, than on the original nature of the atoms it contains. Even the last atom of hydrogen in naphthaline may be thus replaced by chlorine, yielding the body $C_{10}H_7Cl$, which has still the general characters of the type. The peculiarity of this form of substitution (for we must remember that almost all chemical changes consist in substitution of one element for another, as when the oxide of a metal, MO, is converted into the chloride, MCl, or the sulphuret, MS, or the cyanide, MCy, or the sulphate, M_2SO_4, &c., &c., where chlorine, sulphur, cyanogen, and SO_4, are successively substituted for oxygen) is still better seen in the action of nitric acid or naphthaline. The first effect is that 1 eq. of hydrogen is oxidized to water; but the oxygen being taken from nitric acid, NO_3, leaves nitrous acid, NO_2, and this complex atom at once takes the place of the hydrogen removed, forming the compound $C_{10}H_7NO_2$, which has still the typical characters, although the place of 1 eq. of hydrogen is now occupied by a compound, containing 4 eqs. of oxygen; the body of all others most opposite to hydrogen. And this is so far from being a solitary case, that a large proportion of organic compounds, whether acid, basic, or neutral, form analogous compounds, in which hydrogen is replaced by the same number of atoms of nitrous acid, of chlorine, and of bromine, the general character of the compound remaining the same. Chemistry. Many examples might be given. Acetic acid, \( \text{C}_4\text{H}_6\text{O}_2\), HO, acted on by chlorine, yields chloracetic acid \( \text{C}_4\text{Cl}_2\text{O}_2\). Aniline, a base, \( \text{C}_8\text{H}_7\text{N}\), acted on by bromine, yields the base bromaniline, \( \text{C}_{12}\text{Br}\text{N} \). The neutral oil, benzole, \( \text{C}_{12}\text{H}_8 \), yields, with nitric acid, the oil nitrobenzene, \( \text{C}_{12}\text{NO}_4 \).
It is easy to see that in this way a very large number of new compounds may be obtained, and, in fact, such are every day discovered, the experimenter being guided by the laws we have explained. It must be noticed, however, that although the type, generally speaking, is not altered by such substitutions, as we have just seen that the substitution-products from an acid, a base, and a neutral oil, are acid, basic, and oily and neutral, yet the negative energy of the elements substituted for hydrogen is not altogether lost or sunk. For, although we have from aniline, a base, basic substitution products, such as chloraniline, bromaniline, and nitraniline, in all of which 1 eq. of hydrogen is replaced successively by 1 eq. of chlorine, bromine, and nitrous acid, yet when 2 eqs. of hydrogen are thus replaced, the basic properties are much weakened, and when 3 eqs. have been replaced, as in trichloraniline and tribromaniline, these properties are gone, and the compound is neutral. But the very fact that, in this form, 3 eqs. of chlorine, one of which neutralizes the most basic metals, are just sufficient to destroy the basic character of 1 eq. of a feeble base, proves how much the negative character of chlorine, bromine, or nitrous acid is affected by the peculiar position they are made to occupy in the compound molecule, which only allows their negative character to appear to a small extent, when their quantity reaches a certain point.
Such are the general facts concerning types, and the peculiar form of substitution we have endeavoured to explain, by which the type is not materially changed, although hydrogen be replaced by its opposites. These facts are so far from being inconsistent with the existence of compound radicals, that these radicals are themselves, as types, equally capable of this form of substitution with any other compounds. Indeed, in the case of aniline, which is itself a substitution product of another kind, where hydrogen is replaced, not by its opposites, but by its homologues, as we shall presently explain, it is the radical phenyle, \( \text{C}_6\text{H}_5 \), contained in it, that undergoes the substitution of chlorine, bromine, and nitrous acid for hydrogen.
This leads us to consider that other form of substitution, also peculiar to organic compounds, to which we have just alluded, and to its results, namely, the formation of what are called homologous series, involving principles which, in reference to the classification and understanding of organic compounds, and to their artificial formation, are of far greater practical value than any we have yet expounded. Indeed, we can now see that the progress of science must inevitably reduce the whole of organic chemistry, in which, we must remember, only the same three or four elements are perpetually met with, to a collection of homologous series, in which every compound will have its natural place, indicative at once of its origin, its immediate derivation, and its properties both physical and chemical. This is so much the case, that the student, if he have a clear conception of the nature and relations of the series we call homologous, will have a far better idea of organic chemistry than he could have without this, even if we had space to describe the innumerable organic compounds, which, without this guiding principle, would form, as they have long done, a perfect chaos of isolated facts, which no memory could retain, and to which it would be impossible to give a rational or connected form. For this reason, we shall give a full explanation of this part of the subject, referring the reader to larger works for the voluminous details concerning individual compounds which are altogether inconsistent with our space.
Although we cannot yet include nearly all organic compounds in the series we are about to describe, yet a large number of the more important may be thus included, and thus a catalogue of the known homologous series will form the skeleton, as it were, or groundwork of an arrangement, in which all the parts may be seen to be mutually related. Those substances which do not themselves naturally fall into any of the series will be mentioned as groups, according to their natural affinities, and it will be found that they are in most cases related to the series of which we speak, through some of the products of their decomposition or transformation.
Lastly, after giving a brief account of those substances which cannot yet be included in the homologous series, we shall explain the changes which occur in living organisms, so far as these are known.
Homologous Series.
1. These series have gradually, and of late rapidly, developed themselves from the researches of modern chemists. They arise from a kind of substitution, the commonest of all in organic chemistry, in which hydrogen is replaced by certain compound radicals, which, being themselves homologous, of course give rise to homologous series, when substituted for hydrogen in various compounds. The origin of these homologous series of radicals themselves is more obscure; but, whatever that origin may be, these radicals are so related to each other as to constitute what may be called the chief or fundamental homologous series. Of these, more than one are known, but we shall select the best known and most important, which is that of the methylc or ethylic radicals, so called because methyle and ethyle are the two first radicals of the series. Let us consider these two. Methyle is \( \text{C}_2\text{H}_5 \); ethyle is \( \text{C}_3\text{H}_7 \); and they are, in all respects, closely analogous to one another, and, as has been already stated, to hydrogen and metals. Now what is the difference between them? \( \text{C}_2\text{H}_5 - \text{C}_3\text{H}_7 = \text{C}_1\text{H}_2 \). Consequently the difference is \( \text{C}_1\text{H}_2 \) or 2 \( \text{C}_1\text{H}_1 \). So that, by adding \( \text{C}_1\text{H}_1 \) to the formula of methyle, we obtain that of ethyle. To ascertain the true starting point, let us, after subtracting \( \text{C}_1\text{H}_2 \) from ethyle, which leaves \( \text{C}_2\text{H}_5 \) or methyle, subtract the same amount, \( \text{C}_2\text{H}_5 \), from methyle itself, \( \text{C}_3\text{H}_7 - \text{C}_2\text{H}_5 = \text{H} \). Therefore hydrogen is the origin or point of departure of this series of radicals, and we have already seen that they are analogous to hydrogen. On the other hand, let us add to the formula of ethyle, once more \( \text{C}_1\text{H}_1 \), and we have \( \text{C}_4\text{H}_9 + \text{C}_1\text{H}_1 = \text{C}_5\text{H}_{10} \), which is the formula of propyle. Another addition of \( \text{C}_1\text{H}_1 \) to propyle gives \( \text{C}_6\text{H}_{12} \), which is butyle, and again the addition of \( \text{C}_1\text{H}_1 \) to butyle gives \( \text{C}_7\text{H}_{14} \) = amyle, and so on. Such is the nature of this first or fundamental homologous series, and all other homologous series yet known are formed on the same principle of the addition of \( \text{C}_1\text{H}_1 \), neither less nor more, at each step, the starting point alone being different. There is every reason to believe that this first series extends from methyle (or from hydrogen), \( \text{C}_1\text{H}_1 \) to melissyle \( \text{C}_{10}\text{H}_{22} \), although only a few of the radicals, members of this series, are yet known in a separate form.
The first thing to be noticed is, that all the members of the series, being derived from \( \text{H} \) by the addition of \( \text{C}_1\text{H}_1 \) in successive steps, contain, and must contain, invariably 1 eq. of hydrogen more than of carbon. Secondly, for the same reason, the number of equivalents of carbon is in all an even number, or divisible by 2, while that of the equivalents of hydrogen is odd. These facts are expressed by giving to the series the general formula \( \text{C}_n\text{H}_{2n+1} \), in which \( n \) signifies 2, or a multiple of 2 by a whole number. The general formula may also be written \( \text{C}_{2n}\text{H}_{(2n)+1} \). But the former is the simpler mode. The formula \( \text{C}_n\text{H}_{2n+1} \) includes all the radicals of this, the methylc or ethylic series. In this, as in all similar homologous series, the compounds... Chemistry. lowest in the scale, that is, with least carbon and hydrogen, are the least dense, the most volatile, and have the strongest affinities; and these properties vary in proportion to the amount of \( \text{C}_2\text{H}_2 \) added, according to a regular law. The density of the vapour or gas increases, and the boiling point rises with perfect regularity, as we rise on the scale. Methyle and ethyle are gases like hydrogen, at ordinary temperatures; but while methyle requires 20 atmospheres to liquefy it, ethyle is condensed by 2 atmospheres, and the condensed liquid boils under the ordinary pressure at 23° or 9° below the freezing point. Propyle and butyle are oily liquids, the latter boiling at 226°, and amyle is an oily liquid boiling at 311°. Higher in the scale, the radicals are solid, but fusible and volatile; and the higher we go, the higher are the melting and boiling points. This at least is found to be the case in all other homologous series, and is no doubt true in this, although as yet all the radicals high in the scale are not known in the separate state.
2. Such is the first or fundamental homologous series of radicals, homologous with, and analogous to, hydrogen. Now these radicals, in the second and more common form of substitution seen in organic compounds, are substituted for hydrogen, atom for atom, in various compounds, and thus give origin to many homologous series as there are different compounds in which hydrogen can be replaced by these radicals. Hydrogen, \( \text{H} \), is the starting point of the radicals; and water, \( \text{H}_2\text{O} \), is the starting point of their protodizes, so that we have—
| Hydrogen | \( \text{H} \) | |----------|-------------| | Methyle | \( \text{C}_2\text{H}_2 \) | | Ethyle | \( \text{C}_2\text{H}_4 \) | | Propyle | \( \text{C}_2\text{H}_6 \) | | Butyle | \( \text{C}_2\text{H}_8 \) | | Amyle | \( \text{C}_2\text{H}_{10} \) |
and so on, the two series running absolutely parallel. The five protodizes just named are all known, as well as a good many higher in the scale. They are in fact what are called the ethers, oxide of ethyle being common ether. Oxide of methyle or methylic ether is a gas at ordinary temperatures, and the others named are liquids less volatile than ether, while higher in the scale they are solids, as oxide of cetyl, \( \text{C}_5\text{H}_{10}\text{O} \), which is a crystalline solid, like fat or wax. The general formula of this series is \( \text{C}_n\text{H}_{2n+1}\text{O} \).
3. The third homologous series is that of the hydrated protodizes of the radicals, or the alcohols; of which the starting point may be said to be 2 eqs. of water \( \text{H}_2\text{O} \), \( \text{HO} \), which we may suppose to exist, since water can play the part both of acid and base, both negative and positive, and may possibly form double molecules of hydrate of water. At all events we have only to add \( \text{C}_2\text{H}_2 \) to the first equivalent of water, in successive quantities, to obtain the series of the alcohols, which are—that is, the first 5 of them—
| Water | \( \text{H}_2\text{O} \), \( \text{HO} \) | |-----------|----------------------------------| | Hydrated oxide of methyle \( \text{C}_2\text{H}_2\text{O} \), \( \text{HO} \) | Methylic alcohol. | | Ethyle | \( \text{C}_2\text{H}_4\text{O} \), \( \text{HO} \) | Ethylc or common do. | | Propyle | \( \text{C}_2\text{H}_6\text{O} \), \( \text{HO} \) | Propylic alcohol. | | Butyle | \( \text{C}_2\text{H}_8\text{O} \), \( \text{HO} \) | Butylic alcohol. | | Amyle | \( \text{C}_2\text{H}_{10}\text{O} \), \( \text{HO} \) | Amylic alcohol. |
The whole of these alcohols are formed in the peculiar fermentation of sugar, called the vinous or alcoholic fermentation, and all but the first can only be produced in this way, so far as is yet known. When sugar dissolved is placed in contact with yeast, fermentation ensues, and at a certain temperature, if the sugar be pure, only ethylic alcohol and carbonic acid are produced. Dry grape sugar is the substance which ferments. Its formula is \( \text{C}_12\text{H}_{22}\text{O}_{11} \), and in fermentation, \( \text{C}_2\text{H}_2\text{O} \) yield 4 \( \text{CO}_2 \) and 2 \( \text{C}_2\text{H}_5\text{O} \). But when impurities are present, other analogous fermentations, though to a less extent, accompany this one; and in the fermentation of the juice of the grape, but especially of the expressed residue or mark of the grape, and also in that of infusion of grain or of malt, the four other alcohols here named, and one or two others next above them in the scale, are formed. We do not know exactly what are the products of the fermentations which produce them, but they must differ from those of the vinous fermentation. Thus, 3 eqs. of sugar \( \text{C}_12\text{H}_{22}\text{O}_{11} \) may yield 4 eqs. of propylic alcohol \( \text{C}_2\text{H}_5\text{O} \), 4 eqs. of water, 4 \( \text{H}_2\text{O} \), and 12 of carbonic acid, \( \text{12CO}_2 \). Again, 5 eqs. of sugar may yield 4 of amylic alcohol, 12 of water, and 20 of carbonic acid. But the changes may be more complex. All that we know is, that in some circumstances not yet fully investigated, 5 or 6 different alcohols are formed from sugar. The amylic alcohol was discovered in the alcohol from potatoes and grain a good many years ago, and since then in that from the grape. In the latter, the methylic, propylic, butylic, and caproic alcohols have very recently been detected. Methylic alcohol is obtained, however, chiefly from the distillation of wood, and is often called pyroxylic spirit.
The propylic and butylic alcohols are perfectly analogous to the rest, and intermediate in properties between common alcohol and amylic alcohol, or oil of potato spirit, which has long been known. This series exemplifies admirably the nature of a homologous series. The physical properties of the alcohols are graduated in exact proportion to the increased amount of carbon and hydrogen. Thus, the boiling point rises about 34° for each step or addition of \( \text{C}_2\text{H}_2 \); so that knowing the boiling point of one alcohol, we can calculate that of all the rest. This was done with respect to the two newly discovered alcohols before they were obtained, and the result agreed perfectly with the calculation. A good many alcohols are known higher in the scale. Spermaceti yields one of them, cetyllic alcohol \( \text{C}_2\text{H}_{25}\text{O} \), \( \text{HO} \), and two others have been obtained from wax, namely cerotic or ceric alcohol \( \text{C}_2\text{H}_{26}\text{O} \), \( \text{HO} \), and melissic alcohol \( \text{C}_2\text{H}_{27}\text{O} \), \( \text{HO} \). These three are crystalline, fusible, volatile solids, but have a high boiling point. General formula \( \text{C}_n\text{H}_{2n+1}\text{O} \), \( \text{HO} \).
It is unnecessary to repeat in each case the statement, which holds good in all, that the physical properties and chemical affinities, in a homologous series, vary with the amount of carbon and hydrogen; the density and boiling point rising and the affinity diminishing as the carbon and hydrogen increase.
4. The fourth series is that of the hydretes of the radicals of the first series, or positive radicals. The general formula is \( \text{C}_n\text{H}_{2n+1}\text{H} \), \( \text{H} = \text{C}_2\text{H}_2\text{H} \), or \( \text{C}_2\text{H}_2\text{H} \), hyduret of methyle. This is marsh gas, sometimes written \( \text{CH}_4 \). But \( \text{CH}_4 \) is polymeric only with the true hyduret. The next is hyduret of ethyle, \( \text{C}_2\text{H}_4\text{H} \), \( \text{H} = \text{C}_2\text{H}_4\text{H} \). This series consists of gases, liquids, and solids, and it is believed that some kinds of naphtha, and some kinds of paraffine, belong to it. Naphtha may be \( \text{C}_9\text{H}_{18} \), \( \text{C}_9\text{H}_{18} \), \( \text{C}_9\text{H}_{18} \), and the like, and paraffine may be in some cases, \( \text{C}_9\text{H}_{18} \) and \( \text{C}_9\text{H}_{18} \). At all events wax yields paraffine, and the substances in wax contain, as we have seen, \( \text{C}_4\text{H}_{10} \) and \( \text{C}_6\text{H}_{14} \). Marsh gas, \( \text{C}_2\text{H}_4 \), or perhaps \( \text{C}_2\text{H}_4 \), or a mixture of both, is produced by the decay of dead vegetable matter at the bottom of stagnant water; also in coal mines. It is formed artificially in various processes.
5, 6, 7, 8. It will be seen that these four series are closely related together, the first containing the positive radicals, while the others contain compounds of those radicals. But these radicals form many compounds, and each compound of any one radical, as methyle or ethyle, indicates another homologous series. We have seen the oxide, the hydrated oxide, and the hyduret, each belonging to such a series. Now, the chloride of methyle is one of a fifth series, the general formula of which is \( \text{C}_n\text{H}_{2n+1}\text{Cl} \). The iodide belongs to a sixth, of the general formula \( \text{C}_n\text{H}_{2n+1}\text{I} \); the bromide to a seventh; formula \( \text{C}_n\text{H}_{2n+1}\text{Br} \). All these, at least in the lower part of the scale, are volatile ethereal liquids, and become no doubt solid higher up. These series are exactly parallel to those already mentioned. An eighth series consists of the cyanides, which are remarkable as con- Chemistry containing two compound radicals, but otherwise are quite analogous to the rest. These cyanides are interesting from their being either identical or isomeric with the compounds of another series, the nitryles, connected with a second series of radicals, the negative radicals, to be presently mentioned. The cyanides are also interesting; since from them it is possible to reproduce the corresponding alcohols; and in this way we may be able to obtain certain alcohols which could not otherwise be procured.
9. 10. A ninth homologous series is that of the sulphurets of the positive radicals, which, in the lower part of the scale, are ethereal liquids, with an insupportable garlic odour; general formula $C_nH_{n+1}S$. A tenth series consists of compounds of the sulphurets with hydrosulphuric acid, of the general formula $C_nH_{n+1}S + H_2S$. Of these the types are methylo-mercaptan and ethylo-mercaptan, or simply mercaptan, so called from its strong action on oxide of mercury. These two compounds are $C_4H_8$, $S$, $H_2S$ and $C_4H_8$, $S$, $H_2S$, while the corresponding sulphurets are $C_4H_8$, $S$ and $C_4H_8$, $S$. The mercaptans have also a strong and offensive garlic odour. It will be seen that the sulphurets are the oxides or ethers in which sulphur has taken the place of oxygen, and the mercaptans are the hydrated oxides or alcohols, in which the same substitution has taken place; for we have—
| Ethers. | Sulphurets. | Alcohols. | Mercaptans. | |---------|-------------|-----------|------------| | $C_2H_6O$ | $C_2H_6S$ | $C_2H_6OH$ | $C_2H_6SH$ | | $C_4H_{10}O$ | $C_4H_{10}S$ | $C_4H_{10}HO$ | $C_4H_{10}SH$ | | $C_6H_{12}O$ | $C_6H_{12}S$ | $C_6H_{12}HO$ | $C_6H_{12}SH$ |
The two series might be extended as far as any of the others.
11. We now come to another group of homologous series, still containing the same radicals, namely the salts of their oxides, or compounds of the oxides with oxygen acids, or, as they are called, the compound ethers. The ethers are capable of uniting with almost all acids, such as sulphuric, nitric, hyponitrous, carbonic, oxalic, acetic, benzoic, and in fact all organic acids. It is evident that the compounds of each acid with the ethers form a homologous series. We shall merely give as an example of the neutral compound ethers, an eleventh series, the carbonates of the oxides of the second series. Their general formula is $C_nH_{n+1}O.CO_3 = C_{n+1}H_{n+1}O_3$. Those of methyle and ethyle are volatile ethereal liquids, as are indeed the whole class of compound ethers when low in the scale.
12, 13, 14. A twelfth series is that of the acid sulphates of the oxides of the second series. General formula $C_nH_{n+1}O.HO_2SO_4$. These are formed when the alcohols are acted on by excess of sulphuric acid. They are strongly acid, and, when neutralized by fixed bases, form what may be considered either as double salts, or salts of acids containing the ethers along with sulphuric acid. The two first of these acid sulphates are $C_4H_8O.HO_2SO_4$, called sulphomethylic acid, or double sulphate of water and oxide of methyle; and $C_4H_8O.HO_2SO_4$, sulphoethylic—or sulphovinic acid, or double sulphate of water and oxide of ethyle. The rest of the series are perfectly analogous to these. When these two, or any of the others are neutralized with potash, which replaces the water, we obtain the sulphomethylate and sulphoethylate of potash, or double sulphates of potash and oxide of methyle or ethyle, which, in fact, belong to a thirteenth homologous series, since every base forms a new series with these acids. The two acids, with their potash and lime salts, may be thus compared:—
| Acids. | Potash Salts. | Lime Salts. | |--------|--------------|------------| | $C_4H_8O.HO_2SO_4$ | $C_4H_8OKO_2SO_4$ | $C_4H_8OKaO_2SO_4$ | | $C_4H_8O.HO_2SO_4$ | $C_4H_8OKO_2SO_4$ | $C_4H_8OKaO_2SO_4$ |
The lime salts, of course, form a fourteenth series, and here, as in the case of the neutral compound ethers, there is no limit to the number of series, but that of the acids and bases capable of uniting with the oxides of series 2, and the acids of series 12.
15. The next, or fifteenth homologous series that we shall specify, is not only in itself a very remarkable one, but at the same time the source of an infinite number of additional series. It still contains the same positive radicals which have been present in all the series hitherto named. In this one they are combined with amide, $NH_2$, and the result is a series of volatile bases formerly alluded to, homologous with ammonia, which is their starting point, as hydrogen is of the radicals; (for ammonia is amide + hydrogen). They are in the highest degree analogous to ammonia, which is the true type of the volatile organic bases. Their general formula is $C_nH_{n+1}NH_2$, and therefore they contain no oxygen. The formula may also be written $C_nH_{n+1}N$, which makes it easy to remember, that the hydrogen in all of them exceeds the carbon by 3 eqs., and that there is 1 eq. of nitrogen, and no oxygen. The following are a few of those in the lower part of the scale. We have added a third column to show the analogy with ammonia more clearly, in which the radicals, as well as the amide, are represented by their abbreviated symbols:—
Ammonia, $H_2N = NH_2H = AdH$ Methylamine, $C_2H_5N = NH_2C_2H_5 = AdMe$ Ethylamine, $C_2H_5N = NH_2C_2H_5 = AdEt$ Propylamine, $C_3H_7N = NH_2C_3H_7 = AdPr$ Butylamine, $C_4H_9N = NH_2C_4H_9 = AdBu$ Amylamine, $C_5H_{11}N = NH_2C_5H_{11} = AdAyl$
and so on throughout the whole series of radicals.
No series is more striking than this. Its discovery was predicted by Liebig exactly ten years before it was made, and the properties of the compounds belonging to it plainly indicated. The analogy to ammonia is so perfect, that the base nearest to ammonia, methylamine, can hardly be distinguished from it. It is, like ammonia, a gas, absorbed in large quantity by water, of a pungent smell, almost identical with that of ammonia; it forms white fumes with hydrochloric acid, and its salts exactly resemble those of ammonia. It occurs in various decompositions, and in putrefaction, along with ammonia, and it has been frequently taken for ammonia and described as such before its true nature was known. Ethylamine is only a degree less like ammonia, being at ordinary temperatures a very volatile liquid, the smell of which, while analogous to that of ammonia, yet differs from it. It also has been often overlooked from this resemblance. As in all other series, the compounds higher in the scale are less and less volatile and more oily, and at a certain point become solid and crystalline. Not only do these bases form as many new homologous series as there are acids to combine with them, but with them all the reactions of ammonia may be repeated, giving rise to new compounds. Thus, ammonia forms four or five new bases with platinum; so do these volatile bases, methylamine and ethylamine, so that each of these four or five platinum bases represents a new series, and each of their salts with acids represents another. Thus not only do the sulphates of methylamine, &c., form a series, but the sulphate of each of the four or five platinum bases of ammonia does so likewise. And so of all the other salts. The bases of the series are called amide bases.
16. The sixteenth is also one of volatile bases, but not containing amide. Ammonia is still the type, but in this case it is viewed as composed of $NH$, $H_2$, or of imide $NH$, with 2 eqs. of hydrogen. The homologous bases of this series consist of imide with 2 eqs. of methyle, or of ethyle, &c.; or of imide with 1 eq. of methyle and 1 of ethyle, or 1 eq. of ethyle, and 1 of propyle, &c., &c. The following list contains a few of them:—
Ammonia, $H_2N = NH_2H = IdH$ Dimethylamine, $C_2H_5N = NH_2C_2H_5 = IdMe$ Diethylamine, $C_2H_5N = NH_2C_2H_5 = IdEt$ Dipropylamine, $C_3H_7N = NH_2C_3H_7 = IdPr$ Methylpropylamine, $C_2H_5N = NH_2C_2H_5 = IdMePr$ Ethylpropylamine, $C_2H_5N = NH_2C_2H_5 = IdEtPr$ Chemistry, and so on. These bases are very much similar to the others. They are called imide bases, and their general formula is NH₂(CₙHₙ₊₁). It will be seen by the first column, that several of them are isomeric with amide bases, but the second and third columns, which give the rational formulas, show that they are distinct in constitution as they are in properties, although analogous. It must be observed that the general formula of this series NH₂(CₙHₙ₊₁), may also be written (CₙHₙ₊₁)N, which is the same as that of the preceding series in its second form. The same general form also (CₙHₙ₊₁)N, includes also the next series, although it also may be expressed so as to show the difference.
| Ammonia | N₂H₄ | |---------|------| | Trimethylamine | C₃H₇N | | Triethylamine | C₆H₁₅N | | Triamylamine | C₉H₁₉N | | Methylidodethyramine | C₁₀H₂₁N | | Ethylidodiamine | C₁₁H₂₃N | | Methylidodiamine | C₁₁H₂₃N |
Even among the few here given, it will be seen that three are isomeric with bases in the last table, and two of these also with two bases in the first table, series 15. But the rational formulas in the last two columns show that they differ in constitution, as they do also in properties. The bases of this series are called nitryle bases.
The three series just mentioned, of all of which ammonia is the type, include all the known volatile organic bases, natural or artificial, that is, all such as are not decomposed but volatilized, unchanged by a due application of heat. An amide base is easily converted into an imide base by the action of the iodide of one of the radicals of series 1, and an imide base is converted by the same means into a nitryle base. And all of them may be derived from ammonia by the action, in successive steps, of such an iodide. Let us take iodide of ethyle, AeI. The first action is NH₂ + AeI = NH₂Ae₁HI. That is, the iodine takes 1 eq. of hydrogen, forming hydriodic acid, while the ethyle replaces that eq. of hydrogen, forming the amide base, ethylamine, which combines with the hydriodic acid. The next step is the action of iodide of ethyle on ethylamine, NH₂Ae₁ + AeI = NH₂Ae₂HI; the result is, hydriodate of diethylamine. And in the third stage, when iodide of ethyle acts on diethylamine, we obtain the hydriodate of triethylamine, NH₂Ae₂ + AeI = NH₂Ae₃HI. Nothing can show more plainly that all these bases are simply ammonia, the hydrogen of which is replaced, in part or in whole, by positive radicals of series 1. It is also evident, that since there are only 3 eqs. of hydrogen in ammonia, we cannot push further the substitution of these radicals for hydrogen, after we have replaced the whole 3 equivalents. If we attempt to do so, we find that we obtain indeed new bases, but of a different type, being no longer volatile, but decomposed by heat, and containing oxygen. The explanation of this is very interesting. We cannot indeed replace more than three atoms of hydrogen in ammonia by our radicals, but we can add to the 3 eqs. of radical a fourth, and no more, or, in other words, we can replace the fourth eq. of hydrogen also in ammonia, which contains 4 eqs. of hydrogen. This leads to the formation of the next series.
18. The eighteenth series is a most remarkable and interesting one, of fixed bases, that is, bases which cannot be volatilized without decomposition, and which no longer are of the type ammonia, but, in composition, of the type of hydrated oxide of ammonium; and as that body is unknown in a separate form, we can compare them to nothing so well as to hydrated oxide of potassium, or caustic potash, to which they are in a most astonishing degree analogous. To illustrate their formation, let us suppose iodide of ethyle to act on triethylamine. Here there is no more hydrogen left to be replaced, for all 3 eqs. are already replaced, and all the hydrogen present is in the form of ethyle. The action is NH₂Ae₁ + AeI = NH₂Ae₁I. The ethyle of the iodide
17. The seventeenth series is again one of volatile bases, of the type of ammonia, and of the general formula (CₙHₙ₊₁)N, agreeing in this with the two preceding series, as has just been stated. But the more precise formula here is that which is taken from ammonia, viewed, not as amide + 1 eq. hydrogen, nor as imide + 2 eqs. hydrogen, but as nitrogen + 3 eqs. hydrogen, N + H₃. This being the type, in these bases the whole 3 eqs. of hydrogen are replaced by methyle, or by ethyle, &c., partly by one and partly by another of the radicals of series 1. The following are some of them. Their general formula, strictly stated, is N + 3(CₙHₙ₊₁).
| Ammonia | N₂H₄ | |---------|------| | Trimethylamine | N + 3(C₃H₇) | | Triethylamine | N + 3(C₆H₁₅) | | Triamylamine | N + 3(C₉H₁₉) | | Methylidodethyramine | N + 3(C₁₀H₂₁) | | Ethylidodiamine | N + 3(C₁₁H₂₃) | | Methylidodiamine | N + 3(C₁₁H₂₃) |
Unites with triethylamine to form a compound metal, tetrathylum, N Ae₁, analogous to ammonium, NH₄, and this metal unites with the iodine, forming the iodide of tetrathylum, N Ae₁I, exactly similar to iodide of ammonium, NH₄I. To obtain the base, this iodide, which is a crystallizable salt, is acted on by oxide of silver and water. The action is, N Ae₁I + AgO + HO = AgI + N Ae₁HO; and the results are, iodide of silver and hydrated oxide of tetrathylum. The latter is obtained as a crystalline mass by evaporation in vacuo.
In composition, it corresponds to the hydrated oxides of ammonium and potassium. We have—
Hydrated oxide of ammonium... NH₄O, HO = AmO, HO ... potassium... KO, HO ... tetrathylum... Na₄O, HO = ThO, HO
(Tth = Na₄O, tetrathylum). Hydrated oxide of ammonium is not known, as, when we attempt to separate it from the salts of ammonium, it is instantly resolved into ammonia and water. NH₄O, HO = NH₄ + 2HO. The reason of this would seem to be, that the attraction of the oxygen of the oxide for the fourth eq. of hydrogen is so strong as to detach it, that eq. being of course held by a feebler force than the others. If, however, this hydrated oxide could exist in a separate form—and possibly we may some day succeed in obtaining it, perhaps under the influence of intense cold—it would certainly resemble caustic potash, and the hydrated oxide of tetrathylum. The latter can exist in a separate form, just because the attraction of oxygen for the fourth eq. of ethyle is very much less than for hydrogen; that is, at ordinary temperatures; for at higher temperatures hydrated oxide of tetrathylum undergoes precisely the same change as that of ammonium at ordinary temperatures, being converted into ethylamine, corresponding to ammonia, and hydrated oxide of ethyle, corresponding to 2 eqs. of water. N Ae₁O, HO = N Ae₁ + AeO, HO. It is on this account that we conjecture that under intense cold the ammonium compound might be permanent. The action of heat on this hydrated oxide of tetrathylum is characteristic of this whole series of bases.
In properties, hydrated oxide of tetrathylum is so very like caustic potash, that were it not for the action of heat, it might, in solution, be confounded with it. It has a caustic alkaline taste, feels soapy to the fingers, as potash does, attracts water and carbonic acid from the atmosphere, precipitates the salts of metals as potash does, converts oils into soaps when boiled with them, and forms insoluble or sparingly soluble salts, with bichloride of platinum and other tests, exactly as potash does. The chief difference is, that besides the caustic alkaline taste, it has a bitter taste; and this is true of the whole class of bases to which it belongs. This and the action of heat distinguish them from potash and soda. But these same characters connect them with the fixed vegetable bases, such as quinine, morphine, strychnine, Chemistry, nine, and the like; all of which are bitter, and all of which, when heated, yield a volatile nitryl base, as the base in question yields triethylamine. In short, the bases of this series are of the same type as the fixed vegetable bases, and this being so, it is easy to see that there is no improbability in our being able to form artificially the natural fixed organic bases. Before going farther, we shall here give the formulae of a few of the artificial bases of this series, the general formula of which is $N_4 (C_nH_{n+1})O, HO$. They are called ammonium bases.
Hydrated oxide of ammonium (type) $NH_4O, HO = AmO, HO$
Hydrated oxide of tetramethylammonium
$C_{12}H_{26}NO_2 = NMe_4O, HO = TmeO, HO$
$tetramethylammonium C_{18}H_{34}NO_2 = NAeO, HO = ThO, HO$
$tetramethylammonium C_{24}H_{42}NO_2 = NAtyO, HO = AymO, HO$
To show the analogy in composition with the natural fixed bases, let us take the formula of quinine, which is $C_{20}H_{22}NO_2$, which is intermediate between the second and third of those above given. But, in addition to this, there exists a volatile base, found in coal-tar, and formed also by the action of heat on quinine, and bearing to it the same relation that trimethylamine does to hydrated oxide of tetramethylammonium. It is called quinoline, and is a nitryl base.
Now, by the action of iodide of methyl, it is converted into an ammonium base, as follows. Its formula is $C_{12}H_8N$. Now, $C_{12}H_8N + C_2H_5I = C_{12}H_9N, I$. This iodide, acted on by oxide of silver, yields the base, $C_{12}H_9NO, HO = C_{12}H_9NO_2$, which is either quinine or a base isomeric with quinine. It is such considerations which render the ammonium bases so interesting, and we have dwelt somewhat fully on them, as well as on the amide, imide, and nitryl bases, because of the insight thus obtained into the mode of formation of two very important classes of vegetable products, the volatile bases, and the fixed bases. We have dwelt, however, only on the principles which regulate these very curious and important reactions, and not on the individual compounds, which our space forbids us to do. There is no part of the science which so plainly demonstrates the value and importance of the laws we have endeavoured to explain concerning types, substitution, and homologous series. Yet the whole of the facts in reference to these four series of bases are of quite recent discovery, ethylamine and methylamine dating only from 1840, while the imide, nitryl, and ammonium bases have all been discovered much more recently. There is every reason to expect important practical applications of these discoveries; but even should this not be the case, they have already done more for the science than hundreds of practical applications could ever do.
We shall now turn to a group of homologous series, related to those we have described, but more particularly to a series of negative radicals, derived from the compounds of the positive radicals of series I.
19. The nineteenth series here specified, is that of the derived or positive radicals themselves. They are little if at all known in the separate state, but may be traced in many compounds, and therefore it is convenient to assume their existence. They are derived, that is, their compounds are derived, from those of the positive radicals, by the removal of 2 eqs. of hydrogen, which is effected by oxidizing agencies, by chlorine, and otherwise. Their general formula is $C_nH_{n-1}$; and the following are the first in the series—
Formyle... $C_2H_2 = Methyle C_2H_2 - H$
Acetyly... $C_2H_4 = Ethyle C_2H_4 - H$
Propionyle... $C_3H_6 = Propyle C_3H_6 - H$
Butrylyle... $C_4H_8 = Butyle C_4H_8 - H$
Valerylyle... $C_5H_{10} = Amylyle C_5H_{10} - H$
and so on, regularly.
20. The twentieth series is that of the hydrated protoxides of these negative radicals, the general formula of which is $(C_nH_{n-1})O_2HO = C_nH_nO_2$. The type of this series is aldehyde, $C_2H_2O, HO = C_2H_2O$, the hydrated oxide of Chemistry. acetylye. It is called aldehyde, because it is obtained from alcohol by dehydrogenation, for alcohol, $C_2H_2O, HO = H_2 = C_2H_2O, HO$.
Aldehyde is formed whenever alcohol is acted on by oxygen, the first effect being the removal of 2 eqs. of hydrogen, converted by the oxygen into water. Thus, $C_2H_2O, HO + O_2 = 2HO + C_2H_2O, HO$. Aldehyde is a very volatile, pungent, inflammable liquid, having a strong attraction for oxygen, and reducing the salts of silver to the metallic state by this attraction. With 2 eqs. of oxygen it forms pure acetic acid, which is the teroxide of the same radical of which aldehyde is the protoxide. $C_2H_2O, HO + O_2 = C_2H_2O_2, HO$.
The whole series of homologous compounds, which, as a class, are called the aldehydes, agree with this one in their derivation, and in their attraction for oxygen, by which they are converted into volatile acids homologous with acetic acid. Several of them are found in nature, and others are formed in various processes. There are two remarkable characters which are found in all aldehydes, even in such as belong to a different series. But here we speak only of that series of aldehydes which is derived from the ethylic series of alcohols, and yields the acetic series of acids. These characters are, that the aldehydes combine with ammonia, forming in several cases permanent, crystallizable compounds; and that they also form crystalline compounds with the sulphites of potash or ammonia. By one or other of these characters aldehydes are detected when mixed with compounds of different properties, and may be purified. But their most important character is that of absorbing oxygen from the air, and producing the volatile and oily acids of the next series.
The following are a few of the aldehydes:
| Hydrated oxide of formyle... | $C_2H_2O, HO = C_2H_2O_2$ | |-----------------------------|---------------------------| | Do acetylye... | $C_2H_4O, HO = C_2H_4O_2$ | | Do propyle... | $C_3H_6O, HO = C_3H_6O_2$ | | Do butrylyle... | $C_4H_8O, HO = C_4H_8O_2$ | | Do valerylyle... | $C_5H_{10}O, HO = C_5H_{10}O_2$ | | Do deneathyl... | $C_6H_{12}O, HO = C_6H_{12}O_2$ | | Do caprylyle... | $C_7H_{14}O, HO = C_7H_{14}O_2$ |
These and some others are known. The two last-named are found, the former among the products of distillation of castor oil, the latter in the volatile oil of rue.
21, 22. The next, or twenty-first series, is that of the hydrated teroxides of the negative or formylic radicals, which are volatile, and with the exception of two, oily and fatty acids of great interest and importance. Their general formula is $C_nH_{n-1}O_3, HO = C_nH_nO_3$. They are found abundantly in nature, generally combined with oxide of lipyle or glycerine, forming the fixed oils and fats; but they also occur free, and some of them combined with oxide of ethylic. These acids are formed by the direct oxidation of the aldehydes, which, as we have seen, are themselves formed by the action of oxygen on the alcohols, which removes hydrogen from these compounds. Hence the typical process, which is the conversion of common alcohol into acetic acid, consists of two stages, the production of aldehyde by dehydrogenation, and the oxidation of the aldehyde thus produced. Representing alcohol by $C_2H_6O_2$ for shortness' sake, we have first $C_2H_6O_2 + O_2 = 2HO + C_2H_2O_2$; and secondly aldehyde, which is $C_2H_2O_2$, taking up 2 eqs. of oxygen, becomes acetic acid, $C_2H_4O_2 = C_2H_4O_2, HO$. It is in this way, and no other, that alcohol, wine, or beer, is converted into vinegar. If the supply of oxygen be deficient, great loss is sustained by the evaporation of the very volatile aldehyde, but with a full supply of oxygen the whole is acidified. As this oxidation, or slow combustion, or decay, of alcohol is set agoing by contact with a ferment, such as yeast, and air at the same time, it has been called the acetous fermentation; but it is merely a case of oxidation or Of all known homologous series, this one is the best known and the most complete, the series being unbroken from C₂ (in formic acid), to C₁₀ (in behenic acid), and at least two acids being known beyond that point. We give here the list of these acids, promising that the two first, which contain, relatively, a very large amount of oxygen, are not oily, but that oily properties begin to appear in the third, and that all the rest are oily and fatty, exhibiting a perfect gradation of physical properties, such as density, fusibility, volatility, &c.; being, in short, a perfect example of a homologous series.
| Acid | Formula | |-----------------------|---------| | Formic acid | C₂H₄O₂HO = C₂H₂O₃ | | Acetic acid | C₂H₄O₂HO = C₂H₂O₃ | | Propionic acid | C₃H₆O₂HO = C₃H₄O₃ | | Butyric acid | C₄H₈O₂HO = C₄H₆O₃ | | Valerianic acid | C₅H₁₀O₂HO = C₅H₈O₃ | | Caproic acid | C₆H₁₂O₂HO = C₆H₁₀O₃ | | Caprylic acid | C₇H₁₄O₂HO = C₇H₁₂O₃ | | Pelargonic acid | C₈H₁₆O₂HO = C₈H₁₄O₃ | | Capric acid | C₉H₁₈O₂HO = C₉H₁₆O₃ | | Marigolic acid | C₁₀H₂₀O₂HO = C₁₀H₁₈O₃ | | Laurostenic acid | C₁₁H₂₂O₂HO = C₁₁H₂₀O₃ | | Cocinic acid | C₁₂H₂₄O₂HO = C₁₂H₂₂O₃ | | Myristic acid | C₁₄H₂₆O₂HO = C₁₄H₂₄O₃ | | Benic acid | C₁₆H₃₀O₂HO = C₁₆H₂₈O₃ | | Cetyllic and Palmitic acids | C₁₈H₃₂O₂HO = C₁₈H₃₀O₃ | | Margaric acid | C₁₈H₃₂O₂HO = C₁₈H₃₀O₃ | | Bassic and Stearic acids | C₁₈H₃₂O₂HO = C₁₈H₃₀O₃ | | Balenic acid | C₁₈H₃₂O₂HO = C₁₈H₃₀O₃ | | Butinic acid | C₁₈H₃₂O₂HO = C₁₈H₃₀O₃ | | Behenic acid | C₁₈H₃₂O₂HO = C₁₈H₃₀O₃ | | Cerotic acid | C₁₈H₃₂O₂HO = C₁₈H₃₀O₃ | | Mellistic acid | C₁₈H₃₂O₂HO = C₁₈H₃₀O₃ |
The acids of this truly remarkable series are all volatile, that is, may all be distilled unchanged, but the boiling point rises at each step just as with the alcohols, and to the same extent, namely, about 34° for each addition of C₄H₈. The two first are products of oxidation, usually artificial, but formic acid occurs in the ant, and acetic acid in some vegetable juices. The remaining acids are all found in nature, and in general, combined with oxide of lipyle, C₂H₄O₂ or C₆H₁₂O₃, forming the neutral fixed oils and fats, vegetable and animal. Of the former, olive oil and palm oil are examples; of the latter, tallow and butter. These fats and oils, however, contain also a peculiar oily acid, not of this series, combined also with oxide of lipyle. This is oleic acid, C₁₈H₃₁O₂HO = C₁₈H₃₀O₃. The most abundant of the oils and fats are those containing oleic acid, stearic acid, palmitic acid, and margaric acid, which seems to be a compound, possibly a mixture of stearic and palmitic acids. The oils containing the acids lower in the scale, from C₁ to C₅, which are the more volatile of the oily acids, occur only in certain fats, and in small quantities, and give them their peculiar flavour, the fats higher in the scale having neither taste nor smell. The neutral fats are named shortly, after the acids they contain; thus, oleine, stearine, palmitine, margarine, butyrine, valerine, caproine, &c. Solid fats consist chiefly of stearine, palmitine, margarine, &c., with a little oleine; liquid oils of oleine, with some margarine, stearine, &c., dissolved. Butter is a very remarkable fat, containing butine, stearine, palmitine, and myristine, the stearine and palmitine together forming margarine, all of these being solid tasteless fats; and, in smaller quantity, caprine, capryline, caproine, and butyrine, which are oily and sapid, and give to butter its peculiar flavour, especially butyrine, the most abundant of them. It contains also oleine. But it is worthy of notice, that all the acids of the formic series in butter have formulae in which the number of atoms of carbon is divisible by 4, none of the intermediate acids being present. Valerine is the compound which, being present in small quantity in whale oil, as butyrine is in butter, gives to that oil its peculiar and unpleasant flavour. When the neutral fat oils, such as stearine, palmitine (which constitutes the chief part of palm oil), margarine, and oleine, are boiled with alkalis, they yield soaps, which are compounds of the oily and fatty acids with potash and soda, the former yielding soft, the latter hard soaps. In this process the basic oxide of lipyle is separated, and combining with water, forms a sweetish solution, which by evaporation forms a syrup, called glycerine, or the sweet principle of oils. Oxide of lipyle is C₂H₄O₂ and glycerine is 2(C₂H₄O₂) + 3HO = C₆H₁₂O₃. When glycerine is heated in sealed tubes with the oily acids, it again becomes oxide of lipyle and combines with the acids, reproducing neutral oils or fats. When heated by itself glycerine yields an intolerably acid pungent vapour, which condenses into a liquid called acroleine, or hydrated oxide of acryl, C₂H₄O₂HO = C₂H₄O₂. It appears to be either oxide of lipyle, which we have seen to be C₂H₄O₂ or C₆H₁₂O₃, or polymeric with it, the latter being the more probable view. It attracts oxygen with avidity, and is converted into an acid, acrylic acid, C₂H₄O₂HO = C₂H₄O₂ resembling acetic acid. In consequence of the formation of acroleine, the action of heat on oils is an excellent means of detecting the presence in them of oxide of lipyle or glycerine. A drop of any oil containing that compound, heated in the bottom of a test tube, produces the pungent vapour of acroleine which attacks the eyes strongly, and is indeed formed, as all must have perceived, when a candle is blown out so as to leave the wick ignited, that is red-hot, without flame.
The reader will perceive that we have taken this opportunity of giving a brief general sketch of the oils and fats; and have, in fact, appended to the homologous series of the oily acids the description of another series, No. 22, which includes the compounds of those acids with oxide of lipyle or glycerine, that is, the neutral oils and fats. We trust that this brief notice will suffice to give the student an idea of the chemistry of both of these very important series, the oily and fatty acids, and the neutral oils and fats. It will also serve to illustrate the advantage of studying homologous series, since otherwise this numerous class of bodies would present only a mass of confusion.
23. The next, or twenty-third series we shall name is that of the salts formed by the acids of series 21 with oxide of ammonium. We shall not, however, enter into details, but only state, that from this series two others arise by the separation of water. As an example of the series itself, we take acetate of ammonia, NH₄O, C₂H₄O₂. General formula NH₄O + (C₂H₄O₂)O₂.
24. The twenty-fourth series is derived from the preceding by the separation of 2 eqs. of water, and includes the amides of the acids of series 21. Example acetamide, which is acetate of ammonia, minus 2 eqs. of water, NH₄O, C₂H₄O₂ - 2HO = NH₂, C₂H₄O₂ = C₂H₄NO₂. General formula NH₂ + C₂H₄O₂O₂.
25. The twenty-fifth series is derived either from the twenty-third, by the separation of 4 eqs., or from the twenty-fourth by that of 2 eqs. of water, by which all oxygen is removed from both, and the result is a series of very remarkable volatile liquids, called nitriles, and containing the elements of one of the negative radicals, with 1 eq. of nitrogen. Take for example acetonitrile, which is thus derived from acetate of ammonia. NH₄O, C₂H₄O₂ - 4HO = C₂H₄N, or from acetamide; NH₂, C₂H₄O₂ - 2HO = C₂H₄N.
The most important point in regard to this series is, that in composition they are either nitures of the formylic radicals, or cyanides of the methyl radicals one step lower in the scale. Thus acetonitrile is either C₂H₄N, or C₂H₄N, which latter formula is cyanide of methyle.
Now it is not yet certain whether in all cases the nitriles, as obtained from the ammonia salts of the acids of the formic series, are really the cyanides of ethylic radicals, or only Chemistry, isomeric with them. In some cases they certainly appear to be identical with these cyanides as otherwise obtained, but in others they seem to be different. Supposing them to be the cyanides, then it will be possible from any acid of the series No. 21 to obtain the cyanide of the ethylic radical, having 2 eqs. of carbon less than the acid, as from acetic acid cyanide of methyle. Now from the cyanides we can reproduce the alcohol from which they are derivable. And thus we may probably be able to form artificially alcohols which otherwise might never be known. For example, the alcohol with 30 eqs. of carbon is unknown; but from the ammonia salt of the acid with 32 eqs. of carbon, palmitic acid, we can obtain the body palmitonitryle C₉H₁₆N, which is probably the cyanide of the radical C₂₀H₄₀N. And so, from this cyanide it might be possible to form the alcohol in question, which contains the radical C₂₀H₄₀N. The general formula of the nitriles is CₙHₙ₋₁N or CₙHₙ+₁ + CₙN.
26. The next, or twenty-sixth series, will be that of the terchlorides of the formylc radicals, of which chloroform, the terchloride of formyle is the type. The properties of chloroform are now well known. At present no other member of this series has been studied, but judging from that one they merit investigation. General formula CₙHₙ₋₁Cl₃.
27. The oil of olefiant gas, or of the Dutch chemists, represents a twenty-seventh series. It is the hydrochlorate of a protochloride of acetylene, CₙHₙCl₂HCl = CₙHₙCl₂. Of this series also hardly any others are known. The oil in question has a singular resemblance to chloroform in its taste and smell, as well as in its action on the system when inhaled. General formula, CₙHₙ₋₁Cl₂HCl.
28. The twenty-eighth series is that of the hydrates of the formylc radicals, the type of which is olefiant gas, or hydrate of acetylene, CₙHₙH = CₙHₙ+. This is a series of combustible gases, liquids, and solids, formed abundantly in the distillation of organic substances, such as wood, coal, or animal matter, along with the hydrates of the methylic radicals, typified by marsh gas CₙHₙ. It is probable that several species of naphtha and of paraffine belong to this series, as well as to series 4. The compounds of this series, No. 27, are absorbed by chlorine even in the dark, which is not the case with those of series 4.
29. The next or twenty-ninth series is very remarkable; it is that of which oxalic acid is the type, and consists of dibasic acids, having a singular relation to the acids of series 21. Oxalic acid is C₂O₄·2HO = C₂H₂O₄. Now, if we compare this with the formula of formic acid, C₂H₂O₄, we perceive that they differ exactly by C₂O₄, that is, by 2 eqs. of carbonic acid; so that, to obtain the formula of the acids of this series, we have only to add C₂O₄ to those of the acids of series 20, thus—
Monobasic volatile acids. Bibasic fixed acids.
Formic acid, C₂H₂O₄ + C₂O₄ = C₄H₄O₆ oxalic acid.
Acetic acid, C₂H₂O₄ + C₂O₄ = C₄H₄O₆ acetic acid.
Propionic acid, C₃H₆O₄ + C₂O₄ = C₅H₆O₆ succinic acid.
Butyric acid, C₄H₈O₄ + C₂O₄ = C₆H₈O₆ adipic acid.
Valerianic acid, C₅H₁₀O₄ + C₂O₄ = C₇H₁₀O₆ pimelic acid.
Caproic acid, C₆H₁₂O₄ + C₂O₄ = C₈H₁₂O₆ sebacic acid.
Glanthyllenic acid, C₇H₁₄O₄ + C₂O₄ = C₉H₁₄O₆ suberic acid.
Caprylic acid, C₈H₁₆O₄ + C₂O₄ = C₁₀H₁₆O₆
Pelargonic acid, C₉H₁₈O₄ + C₂O₄ = C₁₁H₁₈O₆ sebacic acid.
It will be seen that up to CₙH₂ₙO₄ there are only two blanks in this series; and it is a proof of their close relation to the oily volatile acids, that every one of these, except perhaps the last, is formed, along with the parallel oily acids, in the oxidation of fats and fatty acids by means of nitric acid. It is only very recently that these relations have been recognised and the series established; and as it includes oxalic acid, one of the commonest acids in plants, we are entitled to expect that the progress of science will develop series in which the other acids of acid fruits and leaves will find their place. We have another proof of the close relation between these two series of acids, the formic series and the oxalic Chemistry, series, in the fact that oxalic acid, when heated, yields formic and carbonic acids, which, in the above table, are shown to exist in it by their elements at least. This is, indeed, one of the best methods of obtaining formic acid. It seems probable that we shall succeed in applying the same method to obtain from the other acids of the oxalic series the oily acids parallel to them, as, for example, cinnamhylic acid, from suberic acid, and the rare pelargonitic acid from sebacic acid. This, however, has not yet been done. Sebacic acid is formed when oleic acid is distilled, and the production of it by heat is an excellent test of the presence of oleine in any oil or fat. The oxalic series of acids are all bibasic, and their general formula is CₙHₙ₋₂O₄ = CₙHₙ₋₄O₂·₂HO.
30. The next, or thirtieth series, is that of the cyanates of the oxides in series 2. The type is cyanic acid, which is remarkable for its transformation into urea, when combined with ammonia. Besides this, when heated with potash, it yields carbonic acid and ammonia, CₙNO, HO + 2 KO, HO = 2 (KO, CO₂) + NH₃. Now, the homologous cyanates of oxides of methyle, ethylic, &c., will undergo the same transformations. By the latter, heating with potash, they yield, instead of ammonia, the homologous bases, methylamine, ethylamine, &c., which were discovered by Wurtz in this way. The former metamorphosis, that is, with ammonia, gives rise to the next series, which is a very remarkable one. It is unnecessary to dwell longer on these cyanates, the general formula of which is (CₙHₙ+₁O₂).
31. The thirty-first series is that of which urea is the type. And here we have another example of the comprehensiveness of the principle of homologous series. Urea has long been considered as an isolated body, without any visible relation to others, and now we find that, viewed in the light of the principle alluded to, it is a type of a numerous class of compounds, the discovery of which is due to that principle. The following are the first members of this series:
Cyanic acid, with ammonia—
C₂NO, HO, NH₂ yields C₄H₄N₂O₄ urea.
Cyanate of oxide of methyle, with ammonia—
C₂NO, C₂H₂O₄NH₂ yields C₄H₄N₂O₄ methyo-urea.
Cyanate of oxide of ethyle, with ammonia—
C₂NO, C₄H₄O₂NH₂ yields C₆H₆N₂O₄ ethyo-urea.
Cyanate of oxide of amylo, with ammonia—
C₂NO, C₆H₁₀O₄NH₂ yields C₈H₁₀N₂O₄ amylo-urea.
The perfect analogy which here prevails is fully seen, if we consider hydrated cyanic acid as cyanate of oxide of hydrogen, and the cyanates of oxide of methyle, &c., as compounds in which methyle, &c., replace that hydrogen. The rational formula of urea is not certainly known, but as it is basic, we may suppose it to represent 2 equivalents of ammonia, in which 2 equivalents of hydrogen are replaced by CO₂ or carbolic oxide, thus: N₂H₄ = 2 eqs. ammonia, and urea = N₂H₄ = 2 eqs. ammonia, or N₂H₄(CO₂) = 2 eqs. ammonia.
Urea………………………………………N₂H₄(CO₂)
Methyo-urea………………………………N₂C₂H₄(CO₂)
Ethyo-urea…………………………………N₂C₄H₆(CO₂)
Amylo-urea…………………………………N₂C₆H₁₀(CO₂)
The compounds of this series, homologous with urea, are perfectly analogous to it in properties. Urea, the type, is found ready formed in urine, and is produced artificially by the above-mentioned transformation of cyanate of ammonia. It crystallizes in prisms, which in form as well as in taste resemble nitre. It is soluble in alcohol, and forms with acids salts, being a weak base. The nitrate and oxalate Chemistry of urea are sparingly soluble, and crystallize readily. The action of heat on urea has been already explained, as well as its production, under the head of isomeric and polymeric transformations.
32. The next series we shall mention is that which consists of compounds of the aldehydes with ammonia. Only one of them, that composed of acetic aldehyde and ammonia, is well known; but there is no doubt of the existence of several others, the tendency to form such compounds being a character of the aldehydes. The best known of these compounds, aldehydammonia as it is called, is \( \text{NH}_4\text{HO}, \text{C}_4\text{H}_4\text{NO}_2 \). It crystallizes readily, and undergoes some remarkable transformations. The general formula of this series is \( \text{C}_n\text{H}_{n-1}\text{O}, \text{HO}, \text{NH}_4 \). One of its transformations is that caused by sulphurous acid of which 2 eqs. unite with 1 of aldehydammonia, or 1 eq. of aldehyde unites with 1 eq. of bisulphite of ammonia, to form the compound \( \text{NH}_4\text{HO}, \text{C}_4\text{H}_4\text{O}_2\text{SO}_3 = \text{C}_4\text{H}_4\text{NSO}_3 \). This compound is isomeric with taurine, a very remarkable substance obtained from bile. It is probable that this is one of a new homologous series.
33. The type of the next series is derived from formic aldehyde, by the action of hydrocyanic acid and water, \( \text{C}_2\text{H}_2\text{O}_2 + \text{C}_2\text{NH} + 2\text{HO} = \text{C}_4\text{H}_5\text{NO}_2 \). This last formula is that of a remarkable base, found in bile and elsewhere in the animal body, and from its sweet taste called glycocine, glycooil, or sugar of gelatine. We prefer the first name. It is best obtained by boiling hippuric acid, an acid found in urine, with strong hydrochloric acid, when two eqs. of water are taken up, and it is resolved into benzoic acid and glycocine. Hippuric acid is \( \text{C}_9\text{H}_8\text{NO}_3 \), and with 2 eqs. of water it yields \( \text{C}_9\text{H}_8\text{O}_4 \), benzoic acid, and \( \text{C}_4\text{H}_5\text{NO}_2 \), glycocine. Glycocine is a base, and forms crystallizable salts with acids, but it also forms crystalline compounds with bases and with neutral salts. Of the series of glycocine three only are as yet known, which are—
| Glycocine | \( \text{C}_4\text{H}_5\text{NO}_2 = \text{NH}_4, \text{C}_4\text{H}_5\text{O}_4 \) | | Alanine | \( \text{C}_6\text{H}_5\text{NO}_2 = \text{NH}_4, \text{C}_6\text{H}_5\text{O}_4 \) | | Leucine | \( \text{C}_8\text{H}_7\text{NO}_2 = \text{NH}_4, \text{C}_8\text{H}_7\text{O}_2 \) |
The last column represents these compounds as amides of the acids which constitute the next series. Alanine is obtained by the action of hydrocyanic acid on aldehyde. Leucine is found in the animal body, as is also glycocine. It cannot be doubted that other compounds of this series will be discovered, and they are likely to be compounds of much interest.
34, 35. The next series consists of acids, and the type is lactic acid. They are in so far connected with the aldehydes, that they consist of formic acid, coupled with the aldehydes. Thus we have—
| Glycolic acid | \( \text{C}_2\text{H}_2\text{O}_2 = \text{C}_2\text{H}_2\text{O}_2 + \text{C}_2\text{H}_2\text{O}_2 \) | | Lactic acid | \( \text{C}_3\text{H}_4\text{O}_3 = \text{C}_3\text{H}_4\text{O}_3 + \text{C}_3\text{H}_4\text{O}_3 \) | | Leucic acid | \( \text{C}_4\text{H}_6\text{O}_4 = \text{C}_4\text{H}_6\text{O}_4 + \text{C}_4\text{H}_6\text{O}_4 \) |
The two first acids, if regarded as monobasic, will be written thus—
| Glycolic acid | \( \text{C}_2\text{H}_2\text{O}_2\text{HO} = \text{C}_2\text{H}_2\text{O}_2 \) | | Lactic acid | \( \text{C}_3\text{H}_4\text{O}_3\text{HO} = \text{C}_3\text{H}_4\text{O}_3 \) |
And their ammonia salts, minus 2 eqs. of water, according to the usual law, will give the amides, glycolamide and lactamide, which have the composition of glycocine and alanine, but seem to be only isomeric with them.
Glycolate of ammonia, \( \text{NH}_4\text{HO}, \text{C}_2\text{H}_2\text{O}_2 - 2\text{HO} = \text{C}_2\text{H}_2\text{O}_4, \text{NH}_4 \)
Lactate of \( \text{NH}_4\text{HO}, \text{C}_3\text{H}_4\text{O}_3 - 2\text{HO} = \text{C}_3\text{H}_4\text{O}_4, \text{NH}_4 \)
The reason why these two amides are not identical with glycocine and alanine seems to be that the acids are really dibasic, and that therefore the true formulae of the acids, as well as the amides, are double those just given.
It is probable that the amides form a distinct series by themselves. There is, besides, another series, strictly isomeric with the glycocine series, namely, the hyponitrites of the oxides of series 2.
| Hyponitrite of oxide of methyle | \( \text{C}_2\text{H}_2\text{O}_2\text{NO}_2 = \text{C}_2\text{H}_2\text{NO}_2 \) | | Ethyle | \( \text{C}_2\text{H}_2\text{O}_2\text{NO}_2 = \text{C}_2\text{H}_2\text{NO}_2 \) | | Propyle | \( \text{C}_3\text{H}_4\text{O}_2\text{NO}_2 = \text{C}_3\text{H}_4\text{NO}_2 \) | | Caproyle | \( \text{C}_5\text{H}_6\text{O}_2\text{NO}_2 = \text{C}_5\text{H}_6\text{NO}_2 \) |
The analogue of the first of these in the glycocine series is unknown. The others are analogous to and isomeric with glycocine, alanine, and leucine. This may be called series 35.
36. Another series, isomeric with 33 and 35, is that of which the type is urethan or carbamate of oxide of ethyle. Carbamic acid is an acid amide, or bicarbonate of ammonia minus 2 eqs. of water. \( \text{NH}_4\text{HO}, 2\text{CO}_2 - 2\text{HO} = \text{C}_2\text{H}_2\text{NO}_2 \). This last is carbamic acid, and with oxide of methyle it forms a compound isomeric with glycocine. \( \text{C}_2\text{H}_2\text{O} + \text{C}_2\text{H}_2\text{NO}_2 = \text{C}_4\text{H}_4\text{NO}_2 \). The compound with oxide of ethyle is isomeric with alanine; that with oxide of amyle is isomeric with leucine.
There is still another compound, sarosine, a base, which is isomeric with alanine, but whether it be one of a series we do not yet know.
37. Analogous to the last series is that of the compounds of oxamic acid with the oxides of series 2. They are beautifully crystallized bodies, as are also those of series 36, and are formed by the action of ammonia on the oxalates of the oxides of methyle, ethyle, &c. Oxamic acid is acid oxalate of ammonia, minus 2 eqs. of water. \( \text{C}_4\text{O}_4, \text{HO}, \text{NH}_4\text{O} - 2\text{HO} = \text{C}_4\text{H}_4\text{NO}_2 = \text{C}_4\text{H}_4\text{NO}_2, \text{HO} \), and with oxide of methyle, this acid, oxamic acid, forms the first of the new series. \( \text{C}_2\text{H}_2\text{O} + \text{C}_2\text{H}_2\text{NO}_2 = \text{C}_4\text{H}_4\text{NO}_2 \). This is sometimes called oxamethylan. The next one is oxamethan or oxamate of oxide of ethyle, \( \text{C}_2\text{H}_2\text{O} + \text{C}_2\text{H}_2\text{NO}_2 = \text{C}_4\text{H}_4\text{NO}_2 \).
38. The next series is one consisting of certain newly discovered acids, the two first of which are known. These contain glyolic and lactic acids, coupled with benzoic acid, and thus form a connecting link between the extensive group of allied homologous series now under consideration, and that group to which benzoic acid, its congeners, and their derivatives belong. These acids are—
| Benzyglycolic acid | \( \text{C}_9\text{H}_8\text{O}_5 = \text{C}_9\text{H}_8\text{O}_5 + \text{C}_9\text{H}_8\text{O}_5 \) | | Benzalactic acid | \( \text{C}_9\text{H}_8\text{O}_5 = \text{C}_9\text{H}_8\text{O}_5 + \text{C}_9\text{H}_8\text{O}_5 \) | | Benzenolactic acid | \( \text{C}_9\text{H}_8\text{O}_5 \) is said to exist, but has not yet been studied. The amides of these acids probably form a new series, only one of which is yet known.
39. This is hippuric acid, \( \text{C}_9\text{H}_8\text{NO}_3 \), which is the amide of benzyglycolic acid; that is, benzoglycolate of ammonia, \( \text{NH}_4\text{C}_9\text{H}_8\text{O}_3 \), minus 2 eqs. of HO, which gives \( \text{C}_9\text{H}_8\text{NO}_3 \). This is a very remarkable acid, found in large quantity in the urine of herbivorous animals. When boiled with strong hydrochloric acid, it is first resolved, like other amides, into ammonia and the acid, which is here benzoglycolic acid, 2 eqs. of water being taken up. But the benzoglycolic acid is itself resolved into benzoic acid and glyolic acid, 2 eqs. of water being taken up, and the glyolic acid, acting on the ammonia, produces, with the separation of 2 eqs. of water, glycolamide or glycocine. So that the ultimate results of the operation are benzoic acid and glycocine. Hippuric acid as yet stands alone, but as we already know homologues both of benzoglycolic acid and of glycocine, it cannot be doubted that we shall in time discover homologues also of hippuric acid.
40. The next series we shall mention is that of which acetone is the type. When the salts of acetic acid are decomposed by heat, they yield carbonic acid, which remains combined with the base, and acetone which distils over. In Chemistry, the case of acetate of lime we have CaO, C₄H₈O₃ = CaO, CO₂ + C₄H₈O₂. The true formula of acetone appears to be double of this, or C₄H₈O₂, and it is regarded by some as a hydrated oxide analogous to alcohol; that is, C₄H₈O, HO. This analogy is far from close, but all the acids of the acetic series, at least above acetic acid, seem to form singular compounds, which are isomeric with the aldehydes of the acids next above each. Thus acetone is isomeric with propylaldehyde. Various opinions are entertained as to the real nature, and even as to the formulae of these compounds, but for the present we adopt the formulae which give to all of them 2 eqs. of oxygen.
We now come to a group of homologous series, of very recent discovery, and as yet but little known, save in the case of one or two, but which indicate the existence of a very large number of compounds of the most remarkable composition and properties. These are the compounds in which the elements of the radicals of series 1 are combined with a certain class of metals, giving rise to new and most singular radicals or compound metals having most energetic affinities, and in their compounds very analogous to metals. We can only briefly mention the characters of these compounds.
41. The first series of this group is that which contains zinc. When iodide of methyle or ethyle is heated with zinc in a closed tube, there is formed a crystalline mass, consisting of iodide of zinc, along with the new radical, zinco-methyle in the former, zinco-ethyle in the latter case. On distilling the mass in hydrogen gas, iodide of zinc is left, and the new radicals distil over. They are volatile, fetid, spontaneously inflammable liquids, and appear to act as energetic positive radicals, analogous to metals, combining with oxygen, chlorine, sulphur, &c. They decompose water, producing oxide of zinc and the carbohydrogen of series 4. Thus with zinco-methyle, which is C₄H₈Z₆, and water HO, we have ZnO and C₄H₈; zinco-ethyle is C₄H₈Z₇, and zinco-amyle which has been formed, is C₁₀H₁₁Z₇. No other radicals of this series are yet known.
42. The next series contains antimony. It is formed by the action of an alloy of potassium and antimony on iodide of methyle or ethyle. The formula of stibiomethyle is SbMe₂ = SbC₄H₈. That of stibethyle is SbAc₂ = SbC₁₂H₁₄. These properties resemble those of zinco-ethyle, and they are powerful radicals, of the class of metals.
43. This series also contains antimony. The formula of the first compound is SbMe₂ = SbC₄H₁₁, and it is called stibiomethylum. It is analogous to ammonium and potassium, and forms a hydrated oxide, resembling caustic potash.
44. The next series contains tin, and the compounds are called stannomethyle and stannoethyle. Their formulae are SnC₄H₈ = SnMe₂ and SnC₁₂H₁₄ = SnAc₂. They are analogous to the preceding.
45. In this series, 2 eqs. of the preceding one seem to be condensed into one, so that the formulae are, SnC₄H₈ = SnMe₂, and SnC₁₂H₁₄ = SnAc₂. These also are powerful quasi-metallic radicals.
46. In the next series lead is the metal combined with the organic radicals. A compound has been described, consisting of Pb, Ac₂, which, like the others, is a positive radical, forming a base with oxygen, and salts with chlorine, iodine, &c. There seem to be several other radicals, formed of lead and ethyle, in different proportions. They are all liquid and fuming, and burn when kindled, producing thick fumes of oxide of lead. Each of the lead radicals will of course belong to a distinct series.
47. Tellurium also combines with ethyle to form one or more radicals. The best known is tellurethyle, TeAc = TeC₄H₈. Another, which belongs to a different series, is TeAc₂. They are both very fetid and poisonous liquids, and powerful radicals.
48. Arsenic forms similar compounds, both with ethyle and methyle. The best known of them is kakodyle, AsMe₂ = C₄H₈As₂. This is a crystalline volatile substance, having all the chemical relations of a metal. Its protoxide is a volatile fetid, spontaneously inflammable, and frightfully poisonous liquid, which is strongly basic. Its teroxide is an acid, and is devoid of smell and of poisonous action. Its compounds with chlorine, iodine, sulphur, cyanogen, &c., are all volatile, fetid, and poisonous. There are several other compounds of arsenic with methyle and ethyle, forming so many separate series, but as yet they are little known.
49. The next series we shall mention is typified by kakoplatyle, which consists of kakodyle, platinum, and water, or perhaps oxygen and water. It is also a positive radical, of the formula C₄H₈AsPtO, HO, and forms a hydrated oxide, a chloride, iodide, sulphuret, &c., &c.
50. In the next series, methyle and ethyle are combined with phosphorus. There are several compounds with each, and they appear to correspond to the compounds of phosphorus with hydrogen. The compound PMe₂, which corresponds to kakodyle, is like it a very fetid and poisonous liquid. Besides this, there are the radicals P₂Me₂, PH₂Me and P₂Me₄, all of which are analogous to the first. Each of course indicates a separate series.
We have only indicated the existence of these very remarkable compounds of metals and phosphorus with radicals of the methylic series. Already they are very numerous, and they have all striking properties and strong affinities. New compounds of this class are daily discovered, and almost every new one is the first of a new series. Besides the metals we have named, bismuth and potassium are said to form similar compounds, not yet described. It will be seen that all the metals which have yet been found to unite with the methylic radicals are more or less volatile, and all the compounds are so, whereas the compounds of most of these metals with oxygen, chlorine, sulphur, &c., are fixed in the fire. Most of these compound radicals or compound metals are spontaneously inflammable in the air, from their strong attraction for oxygen, and most of them are poisonous in the highest degree, apparently because they bring the metals they contain in contact with the system in a very fine state of division.
We have now indicated most of the established homologous series, connected with the methylic radicals. It will be seen that these include a large number of important organic compounds, such as alcohol, ether, compound ethers, volatile and oily acids and their salts, volatile and fixed bases and their salts, carbohydrogens, amides, &c. There are, however, many compounds which cannot as yet be classified in this way. But before turning to these, we must mention another group of homologous series, not directly connected with the methylic radicals, but rather in some points running parallel to the series already described. This is the benzoic group, so called from benzoic acid, which is a characteristic feature of the group.
1. The first series of this group is that of which benzoic acid is the type. This acid is found ready formed in gum benzoin, and is also produced by the oxidation of hyduret of benzoyle, by the decomposition of hippuric acid, so that it often occurs in the urine of herbivora, and among the products of the oxidation of such bodies as fibrine, albumen, &c. Its formula is as follows, with those of its homologues:
| Benzoic acid | C₆H₅CO₂HO | |-------------|-----------| | Toluic acid | C₆H₅CH₃CO₂HO | | Xylic acid | C₆H₅CH₂CO₂HO | | Camphoric acid | C₁₀H₁₆O₃ |
The third acid is hardly known, but some of its derivatives are known, and are perfectly homologous with those of benzoic acid. Toluic acid is connected with substances found in balsam of Tolu, and cuminic acid with those found in oil of cumine. These acids are all crystallized, Chemistry, volatile, soluble in water and in alcohol, and approach in characters to resinous bodies.
2. In the next series are those compounds of which the type is hyduret of benzoyle. This is an oily liquid, found in the oil of bitter almonds with hydrocyanic acid. These substances, with others, are formed in the fermentation of amygdaline, a substance peculiar to bitter almonds. The hyduret when pure is $C_{14}H_{8}O_{2} = C_{14}H_{8}O_{2}$. It absorbs 2 eqs. of oxygen from the air, and is soon converted into benzoic acid; $C_{14}H_{8}O_{2} + O_{2} = C_{14}H_{8}O_{3}$. It may be viewed as the hyduret of the radical benzoyle, $C_{14}H_{8}O_{2}$; and this radical, with 1 eq. of oxygen, forms dry benzoic acid, $C_{14}H_{8}O_{2} + O = C_{14}H_{8}O_{3}$. At the same time the hydrogen is converted into water, which combines with the dry acid to form the crystals $C_{14}H_{8}O_{3} + H_{2}O = C_{14}H_{8}O_{4}$. The oil of cumine, $C_{14}H_{8}O_{2}$, may be viewed as the hyduret of cumyle, $C_{14}H_{8}O_{2}$, and is homologous with it. These hydurets may be regarded as the aldehydes of the acids they yield.
3. The next series may be that of the radicals, benzoyle, cumyle, &c. They are hardly at all known.
4. The next is that of the amides of the acids of series 1. Benzamide, tolylamide, cuminamide, &c. Benzamide is benzoyle + amide, or $C_{14}H_{8}O_{2}NH_{2}$, and the others are analogous.
5. The next may be that of chloride of benzoyle, $C_{14}H_{8}O_{2}Cl$.
6. The next, that of cyanide of benzoyle, $C_{14}H_{8}O_{2}Cy$.
7. The next may be that of sulphuret of benzoyle, $C_{14}H_{8}S$. Many more might be added, but these will suffice to illustrate the compounds in which benzoyle, $C_{14}H_{8}O_{2}$, may be traced.
8. The next series contains products of decomposition of the acids of this series. When benzoic acid is heated with excess of lime, it is resolved into 2 eqs. of carbonic acid, containing all its oxygen, and a remarkable carbhydrogen, containing all the hydrogen, $C_{14}H_{8}O_{2} + 2CaO = 2(CaO, CO_{2}) + C_{14}H_{8}$. This last is benzoyle, or hyduret of phenyle, $C_{12}H_{6}$. It is a somewhat fragrant liquid, which is found also in coal tar. Four homologous liquids are known, which are toholole, $C_{14}H_{8}$; xylole, $C_{16}H_{10}$; cumole, $C_{18}H_{12}$; and cymole, $C_{20}H_{14}$.
9. The next series is that of which the radical phenyle, $C_{12}H_{6}$, is the type. They are not known in the separate state, but enter into many compounds, the bodies of the last series being their hydurets. They have some analogy to the methyllic radicals.
10. The next series is that of the hydrated oxides of the phenyllic radicals. Hydrated oxide of phenyle, the type, $C_{12}H_{6}O$, is found in coal tar, and often called carbolic acid. It much resembles creosote, and it is most probable that the compound next to it, $C_{14}H_{8}O_{2} = C_{14}H_{8}O_{2}HO$, is creosote itself.
11. We next come to the compounds of the phenyllic radicals with amide, which, as in the case of the ethylic radicals, are volatile bases. The first of them is phenylamine or aniline, $C_{14}H_{8}N = C_{14}H_{8}NH_{2}$, $NH_{2} = NH_{2}Ph (Ph = C_{14}H_{8})$. It is an oily base, distinguished by the great tendency of its salts to crystallize. Its homologues are solid but fusible, and quite analogous to it. We have—
| Phenylamine | $C_{14}H_{8}N = NH_{2}$ | |-------------|------------------------| | Toluidine | $C_{14}H_{8}N = NH_{2}$ | | Xylidine | $C_{14}H_{8}N = NH_{2}$ | | Cumylamine | $C_{14}H_{8}N = NH_{2}$ | | Cymylamine | $C_{14}H_{8}N = NH_{2}$ |
Aniline is obtained by heating indigo with potash, and is also found, with some of the others, in coal tar and animal oil, that is animal tar oil. In this oil, obtained by distilling bones, there is another homologous series of volatile bases, discovered by Dr Anderson, isomeric with these, but far more volatile. The first of them, picoline, is isomeric Chemistry, with aniline, lutidine with toluidine, &c.
12. There are no compounds which yield a greater number of substitution products than those we are here reviewing. In the first place, besides the amide bases above given, there are two other series, imide and nitryl bases, of which the types are diphenylamine, $NH_{2}Ph$, and triphenylamine, $NPh_{3}$. These also have their homologues, and form two new series. Then aniline, by replacement of its own hydrogen by chlorine, bromine, &c., and nitrous acid, yields such compounds as chloraniline, dichloraniline, trichloraniline, bromaniline, dibromaniline, tribromaniline, nitraniline, dinitraniline, and others, in which 1, 2, or 3 eqs. of the hydrogen of the radical phenyle in aniline are replaced by the elements just mentioned. To take an example or two, we have—
| Aniline | $NH_{2}C_{12}H_{6}$ | |---------------|---------------------| | Chloraniline | $NH_{2}C_{12}H_{6}Cl$ | | Dibromaniline | $NH_{2}C_{12}H_{6}Br_{2}$ | | Nitraniline | $NH_{2}C_{12}H_{6}NO_{2}$ |
Most of these are basic and crystallize well. The homologues of aniline yield similar products, so that each is the commencement of a series.
13. Besides this, the hyduret of phenyle, or benzole and its homologues, also yield similar substitution products with chlorine, bromine, and nitrous acid. Thus we have, with others,
| Benzole | $H_{2}C_{12}H_{6}$ | |---------------|-------------------| | Nitrobenzole | $H_{2}C_{12}H_{6}NO_{2}$ | | Dinitrobenzole| $H_{2}C_{12}H_{6}NO_{4}$ | | Chlorobenzole | $H_{2}C_{12}H_{6}Cl$ | | Bromobenzole | $H_{2}C_{12}H_{6}Br$ |
These compounds, each of which represents or typifies a new homologous series, give rise also to various reactions, producing other compounds. But even without this, we have here another large group of homologous series.
14. Another considerable group consists of the various substitution products derived from benzoic acid itself. For example, there is nitrobenzoic acid. Benzoic acid, $C_{14}H_{8}O_{2}$, or rather $C_{14}H_{8}O_{2}HO$, has one of the 5 eqs. of hydrogen in the anhydrous acid replaced by nitrous acid, and gives the new acid, $C_{14}H_{8}O_{2}NO_{2}$, $O_{2}HO$. Then there is bromobenzoic acid, as well as others, each of which typifies a series.
Here also might be added two other series, namely, that of benzoglycolic acid and that of its amide, which is hippuric acid; but these have been already noticed among the series connected with the ethylic radicals. These two series, in fact, serve to connect the benzoic with the ethylic group of homologous series.
Hyduret of benzoyle gives rise to a very large number of new compounds, by the various reactions it undergoes with different substances, such as bases, ammonia, sulphuret of ammonium, &c. &c. Among these new products are several remarkable bases, such as amarine, sophine, and picrine. It is not known that these belong to homologous series, but it is probable.
Allied to the benzoic group are some others, of which but few members are yet known.
Thus oil of anise and oil of estragon yield when oxidized by nitric acid an acid, anisic acid, $C_{14}H_{8}O_{2}$. Oil of Gaultheria procumbens contains, in union with oxide of methyle, an acid called salicylic acid, because it can be formed artificially from salicine, the bitter principle of willow-bark. Sal- Chemistry: salicylic acid is \( \text{C}_9\text{H}_6\text{O}_3 \), and is therefore homologous with anisic acid.
There are also the hydrures of salicylic and of anisyle, which bear the same relation to these two acids as hydruret of benzoyle does to benzoic acid. Hyduret of salicylic is the oil of spiraea, and is isomeric with benzoic acid, \( \text{C}_{14}\text{H}_{12}\text{O}_3 = \text{C}_9\text{H}_6\text{O}_3 \cdot \text{H}_2\text{O} \).
There are many interesting compounds connected with salicylic acid and hydruret of salicylic, and these probably belong to homologous series, as the two bodies themselves do.
Again there is oil of cinnamon, which yields hydruret of cinnamyle, \( \text{C}_9\text{H}_6\text{O}_3 \cdot \text{H}_2\text{O} \), and this by oxidation becomes cinnamic acid, \( \text{C}_9\text{H}_6\text{O}_3 \cdot \text{H}_2\text{O} = \text{C}_9\text{H}_6\text{O}_3 \). This acid is very analogous to benzoic and salicylic acids. Heated with lime, it yields the carbolhydrogen \( \text{C}_9\text{H}_6 \) analogous to benzole or hydruret of phenyle, along with 2 eqs. of carbonic acid. It is probable that these compounds are each members of new homologous series, and that these series are nearly allied to those of the benzoic group.
Having thus very briefly indicated the existence and nature of a large number of homologous series, we must shortly notice those compounds which cannot as yet be reduced to such series, although we have every reason to expect that in time they may be so classified.
These we must notice very briefly, but as they form certain well-marked natural groups, it will be possible, in small space, to convey a general notion of their nature and properties.
1. Organic Acids.
These are numerous, and it is but in very few cases that we know, as yet, anything about their constitution, that is, about the radicals they contain. We have seen that something is known, in that respect, of formic and acetic acids, of the oily acids homologous with these, of oxalic acid, and of benzoic acid and its congeners.
The commonest of the vegetable acids not yet noticed are the following, oxalic acid being prefixed, as having a great analogy in properties with most of them, and as being of all the simplest in composition. These acids are all crystallizable, soluble in water, and, with one or two exceptions, sour to the taste. As a general rule the number of eqs. of oxygen exceeds that of hydrogen; and lastly, they are either monobasic or polybasic, as indicated by the number of eqs. of basic water in each:
- Oxalic acid \( \text{C}_2\text{O}_4 \cdot 2\text{H}_2\text{O} = \text{C}_2\text{H}_2\text{O}_4 \) - Fumaric and aconitic acids \( \text{C}_4\text{H}_6\text{O}_4 \cdot 2\text{H}_2\text{O} = \text{C}_4\text{H}_6\text{O}_4 \) - Gallic acid \( \text{C}_7\text{H}_6\text{O}_5 \cdot 2\text{H}_2\text{O} = \text{C}_7\text{H}_6\text{O}_5 \) - Racemic and tartaric acids \( \text{C}_4\text{H}_6\text{O}_6 \cdot 2\text{H}_2\text{O} = \text{C}_4\text{H}_6\text{O}_6 \) - Malle acid \( \text{C}_4\text{H}_6\text{O}_6 \cdot 2\text{H}_2\text{O} = \text{C}_4\text{H}_6\text{O}_6 \) - Citric acid \( \text{C}_6\text{H}_8\text{O}_7 \cdot 3\text{H}_2\text{O} = \text{C}_6\text{H}_8\text{O}_7 \) - Mesoic acid \( \text{C}_6\text{H}_8\text{O}_7 \cdot 3\text{H}_2\text{O} = \text{C}_6\text{H}_8\text{O}_7 \) - Tannic acid \( \text{C}_7\text{H}_6\text{O}_6 \cdot 3\text{H}_2\text{O} = \text{C}_7\text{H}_6\text{O}_6 \) - Kinic acid \( \text{C}_8\text{H}_6\text{O}_6 \cdot 2\text{H}_2\text{O} = \text{C}_8\text{H}_6\text{O}_6 \)
Citric acid is found in the juice of the fruits of the orange or citron tribe, and in other acid fruits, as in the currant. Malic acid occurs in unripe fruits of the apple and pear tribe, especially in the fruit of the mountain ash or service tree. Tartaric acid is found in the grape as acid tartrate of potash, and racemic acid, which is isomeric with it, occurs only in the grapes of certain districts. Oxalic acid occurs in wood sorrel, Oxalis acetosella, and in the leaf stalks of rhubarb; also in other plants, as acid oxalate of potash; in lichens, Sedum, Sempervivum, &c., as oxalate of lime. Fumaric acid occurs in fumaria, aconitic acid in aconite and equisetum, meconic acid only in opium, the juice of the poppy, and kinic acid in cinchona bark. Tartaric acid and gallic acid, which are not sour, but astringent, are found in nutgalls, oak bark, and other astringent vegetables.
The frequency of polybasic, especially dibasic and tribasic acids, among vegetable acids, gives rise to many acid salts, such as the acid tartrate and acid oxalate of potash, and to many double salts, as the tartrate of potash and soda, and the tartrate of potash and antimony, Rochelle salt, and tartar emetic.
The neutral salts of vegetable acids with lime, oxide of lead, and oxide of silver, are usually insoluble, or if not, sparingly soluble. As there is a general analogy in composition, especially in regard to the excess of oxygen over hydrogen, so there is a general analogy in properties. But the astringent acids above named, and others like them, strike a deep blue or green colour, approaching to black, with the salts of iron; and kinic acid, in which the oxygen only equals the hydrogen, is a very weak acid.
Like all vegetable products, these acids, and all similar to them, are formed by the plant from carbonic acid and water, which contain the elements of all of them. But if we take as many eqs. of carbonic acid as the acid contains of carbon, and as many eqs. of water as it contains of hydrogen, which of course is the smallest quantity that can yield a given acid, we shall find that these materials always contain more oxygen than the acid formed from them. In other words, the plant in forming them deoxidizes carbonic acid and water, more or less, and thus oxygen, so removed, is given out as gas. Thus, oxalic acid, \( \text{C}_2\text{H}_2\text{O}_4 \), cannot be formed from less than 4 eqs. of carbonic acid and 2 of water, which are \( \text{C}_2\text{H}_2\text{O}_4 \), so that in this case 2 eqs. of oxygen are given out. All the other acids contain a smaller proportion of oxygen than oxalic acid, and therefore, in their formation, more oxygen is given out. Moreover, they may be formed either from carbonic acid and water, or from oxalic acid and water, or from any acid containing more oxygen than themselves; and it is probable that it is in this way by a succession of steps, that the plant produces all the vegetable acids, of which only the chief have been given above.
2. Neutral and Mild Organic Compounds.
Kinic acid, in which the hydrogen and oxygen are equal, leads to the next group, in all of which that is the case. They are few in number, but very abundant, widely distributed, and of great importance, as they constitute the chief mass of the vegetable kingdom. They are mild in character, and generally tasteless or sweet. They are as follows:
- Woody fibre or cellulose, \( \text{C}_6\text{H}_{10}\text{O}_5 \) - Woody fibre or cellulose, \( \text{C}_6\text{H}_{10}\text{O}_5 \) - Starch \( \text{C}_6\text{H}_{10}\text{O}_5 \) - Cane sugar \( \text{C}_6\text{H}_{12}\text{O}_6 \) - Gum \( \text{C}_6\text{H}_{12}\text{O}_6 \) - Grape sugar, dry \( \text{C}_6\text{H}_{12}\text{O}_6 \) - Grape sugar, crystallized \( \text{C}_6\text{H}_{12}\text{O}_6 \)
In consequence of the equality between the oxygen and hydrogen in these compounds, they may be viewed as formed of carbon plus water; or, in other words, in forming them from carbonic acid and water, either directly or indirectly, that is, by successive steps, the plant gives out exactly as much oxygen as was contained in the carbonic acid from which they were derived. Hence their formation follows that of the acids, and they are probably formed in general from these acids, which would account for the uniform presence of the latter in vegetable juices.
Another fact, depending on the circumstance that they all contain 12 eqs. of carbon, and differ only in the amount of water, or its elements, is this: that all before grape sugar in the table may be converted, even artificially, into that kind of sugar. The conversion of starch into sugar constantly takes place in germination, as in malting, and that of both starch and woody fibre into sugar occurs in the ripening of fruits. In these processes, it is effected by the contact of a ferment. It consists in the addition of water or of its elements. The same result is obtained artificially by boiling them with diluted sulphuric acid, and also, in the case of starch, by adding an infusion of malt. Woody fibre is insoluble in all solvents, and perfectly indifferent. Its most remarkable character is that of forming gun-cotton, or nitro-cellulose, when acted on by nitric acid. In that case, 2, 3, or more eqs. of nitric acid are taken up, while water is in some cases expelled, in others not. Gun-cotton is, in some instances at least, $\text{C}_6\text{H}_8\text{O}_4 + \text{NO}_3$, so that if formed from cellulose $a$, 4 eqs. of nitric acid are taken up; if from cellulose $b$, 2 eqs. of water are given out at the same time. But there are several varieties of gun-cotton.
Woody fibre, by long digestion with alkalies or acids, is partially converted into a substance which, like starch, strikes a blue with iodine.
Starch consists of small grains, which are said to be hollow sacs, formed of an insoluble membrane, containing a soluble jelly. Others say that the grains are formed of successive layers of insoluble matter. Hot water causes them to swell and burst, allowing the contents to escape. The leading characters of starch are the becoming deep blue with iodine, and the being converted into sugar and rendered soluble by acids and by ferments. Before becoming sugar, it passes through an intermediate stage, in which it is dissolved as dextrine or gum.
Cane sugar is known by its crystals, and by being more soluble and sweeter than grape sugar. In contact with acids or a ferment, it becomes grape sugar, and then, but not before, it undergoes fermentation.
The action of the ferment appears to depend on its being in a state of decomposition, consequently of molecular motion; and this motion, communicated to the molecules or rather to the atoms of the sugar, suffices to destroy the existing equilibrium and produce a new one. Sugar undergoes several different fermentations, which we shall mention under grape sugar.
Gum is tasteless, viscid, soluble in water, insoluble in alcohol. By the action of nitric acid it is converted into mucic acid, $\text{C}_{12}\text{H}_{10}\text{O}_{14}$, 2 HO, and not, like sugar, into oxalic acid.
Grape sugar is distinguished from cane sugar by being less soluble and less sweet, and also by being easily decomposed into brown products by heating with diluted alkalies. It is the only kind of sugar which undergoes fermentation; all the others are first converted into grape sugar and then ferment.
When the ferment is yeast, or vegetable fibrine in a state of decomposition, the vinous fermentation takes place in solution of sugar. The juice of the grape and infusion of malt both contain sugar and fibrine, and only require to be exposed to the air. But if the air be carefully filtered, by being made to pass through tubes filled with cotton, no fermentation takes place. Hence, and because certain low organisms appear in fermenting liquids, it is probable that the change is induced in the ferment, not as was supposed by the oxygen of the air, but by the introduction of the minute spores or germs of these organisms, which find an appropriate soil in the fibrine. The vinous fermentation is expressed by the equation—
$$\text{C}_{12}\text{H}_{10}\text{O}_{14} = 4 \text{CO}_2 + 2 (\text{C}_4\text{H}_6\text{O}_2)$$
We have already stated that other allied fermentations take place, by which propylie, butylic, amylic, and other alcohols are formed along with common alcohol, but in small quantity. In these, water is probably also one of the products.
When caseine is the ferment, sugar, at the temperature of from 70° to 90°, is converted into lactic acid, or undergoes the lactic fermentation, which is this:
$$\text{C}_{12}\text{H}_{10}\text{O}_{14} = \text{C}_{12}\text{H}_{10}\text{O}_{10}, 2 \text{HO}$$
With the same ferment at a rather higher temperature, lactic acid undergoes the butyric fermentation, especially if first neutralized. The change is—
$$\text{Lactic acid.} \quad \text{Butyric acid.}$$
$$\text{C}_{12}\text{H}_{10}\text{O}_{14} = \text{C}_4\text{H}_6\text{O}_4 + 4 \text{CO}_2 + \text{H}_2$$
There is another fermentation not yet fully understood, but which occasionally accompanies the lactic fermentation. In this, sugar disappears, and we find only gum and mannite. Mannite is $\text{C}_6\text{H}_{12}\text{O}_6$, or $\text{C}_{12}\text{H}_{22}\text{O}_{11}$; and as gum is $\text{C}_{12}\text{H}_{22}\text{O}_{11}$, it is not easy to see where the mannite gets the excess of hydrogen. Probably some other substance is formed which has escaped notice as yet. It must contain an excess of oxygen, and is therefore probably an acid.
Sugar of milk has the same formula as dry grape sugar, and passes into that form by contact with acids and ferments.
In consequence of its being the only source of the compounds of ethyle, such as alcohol and ether, as well as of other alcohols and ethers, sugar is closely connected with the ethylic group of homologous compounds. We know nothing of its intimate constitution, except that, although resolved into alcohol and carbonic acid by fermentation, it does not seem to contain carbonic acid, nor consequently alcohol, ready formed. For by the action of permanganate of potash it is entirely converted into oxalic acid and water, which implies the addition to its elements of 18 eqs. of oxygen. Now, since carbonic acid is the ultimate product of the full oxidation of carbon in all organic compounds, it is hardly conceivable that oxalic acid, which is an inferior stage of oxidation, should be the sole product of the oxidation of carbon in a substance where any part of that carbon was already in the form of carbonic acid. We cannot, therefore, regard sugar as a compound of ethyle, and for the present must consider it as an appendix to the ethylic series, without knowing the precise relation between them.
Besides the kinds of sugar we have named, all of which pass into grape sugar, and in that form undergo fermentation, there appears to be a kind of sugar which is uncrystallizable, but which is probably rendered so by the presence of impurities. Molasses, or the syrupy uncrystallizable mother liquor from the cane juice is rendered uncrystallizable by the action of bases on the sugar during the evaporation, which produces two brown acids, glucic and melassic acids, the presence of which deprives a great part of the sugar of its power of crystallizing. This source of loss is now greatly diminished by carefully neutralizing with acid the lime used in clarifying the cane juice, and also by evaporating in vacuo, at a low temperature. The uncrystallizable sugar in molasses, and that in the residues of the cane, may be fermented, and yields the spirit called rum, which when new contains a trace of butyric acid, derived, no doubt, from a small portion of sugar having undergone the lactic and butyric fermentations. This butyric acid, on keeping, gradually combines with oxide of ethyle from a portion of alcohol, producing butyric ether, and the spirit thus acquires its very peculiar and fragrant odour, as well as the pleasant flavour of pine-apple. In Germany, rectified potato spirit, being first purified by rectification from all the oils which make the crude spirit so coarse in flavour, is converted into highly-flavoured rum by the addition of a very minute quantity of butyric ether artificially prepared. The presence of this ether in the pine-apple, to which it gives the flavour, is one of the few instances of the occurrence of a compound of ethyle as a natural product, and even here it derives its origin from sugar.
It is entirely in the form of sugar that all the starch in seeds, which usually contain it, becomes available in germination for the growth of the first stem and leaves; and it is in the same form that the starch in the food of man and animals enters the circulation, and is enabled to perform its proper function of supporting, by its slow oxidation, the animal heat. Here we see the extreme importance of the tendency in an organic substance like starch to undergo Chemistry, isomeric transformation, for starch and grape sugar, differing only by 2 HO, may be held as isomeric. In the insoluble form of starch, this important element of food is stored up till required; and whether in germination or in digestion, for these processes are almost exactly the same, is rendered soluble and conveyed into the circulation or the juices of the animal or the plant. The reader will also observe that cellulose or woody fibre is most probably formed from sugar by another transformation of the same kind, in which water is separated.
3. Neutral Compounds; bitter, acrid, coloured, or yielding colours with ammonia.
In this group, which is a very numerous one, but formed of compounds generally limited to families, genera, or even species of plants, we include such bodies as the following. In their formation, the deoxidizing process has been carried a step farther than in the last group, for not only all the oxygen of the carbonic acid (or a quantity equal to it), but also a part of that of the water, has been given out. In the vegetative process, therefore, they are naturally produced after, and in all probability from, the substances of group 2.
| Mannite | C₆H₁₀O₅ or C₂₂H₄₁O₁₃ | |---------|----------------------| | Parietine | C₁₀H₁₄O₅ | | Antiarine | C₁₄H₁₄O₅ | | Smithicine | C₁₅H₁₄O₅ | | Quassine | C₁₈H₁₄O₅ | | Elaterine | C₁₉H₁₄O₅ | | Salicine | C₁₉H₁₄O₅ | | Pectine | C₁₉H₁₄O₅ | | Hematoxyline | C₁₉H₁₄O₅ | | Limonine | C₁₉H₁₄O₅ | | Calceine | C₁₉H₁₄O₅ | | Phloridzine | C₁₉H₁₄O₅ |
We must observe that all of these formulae are not absolutely ascertained, and that few of these substances have been as yet fully studied. But the general character of their formulae is no doubt correct, and some, such as mannite, orcin, salicine, pectine, and phloridzine, are well known. As to their properties, mannite, as it is close to sugar in composition, so is it also in taste and mildness. Antiarine and elaterine are acrid and virulent poisons; quassine, salicine and phloridzine are bitter and febrifuge; pectine and pectic acid, a body closely allied to it, form the vegetable jelly of the juices of plants, such as the apple, currant, or carrot juices, and in fact are almost universally present. Hematoxyline is the red colouring principle of logwood, and is a type of a class hardly studied as yet. Orcine, which crystallizes beautifully, is a colourless principle found in some lichens, which, with ammonia, gives rise to the fine and permanent blue dye called archil, and is also a type of an interesting class of compounds recently investigated with great success by Schumke and others, particularly by Stenhouse. The rest are devoid of marked characters. This list is only a selection from a very large number of similar bodies, which, for the most part, have yet to be investigated, and on which, therefore, we need not dwell.
4. Oxygenated Volatile Oils, and Volatile Acids derived from them.
These we have already noticed under the head of the benzoic group. They are strongly marked in character, and in forming them the deoxidizing process has been carried still farther, as may be seen in the following list, which includes only the most important of them.
| Oil of bitter almonds | C₁₁H₁₄O₅ | | Benzoe acid | C₁₁H₁₄O₅ | | Oil of spruce | C₁₁H₁₄O₅ | | Salicylic acid | C₁₁H₁₄O₅ | | Oil of anise | C₁₁H₁₄O₅ | | Anisic acid | C₁₁H₁₄O₅ | | Cumarine | C₁₁H₁₄O₅ | | Cumic acid | C₁₁H₁₄O₅ |
Oil of cinnamon | C₁₀H₁₄O₅ | Cinnamic acid | C₁₀H₁₄O₅ | Oil of camphor | C₁₀H₁₄O₅ | Cuminal acid | C₁₀H₁₄O₅ |
It will be seen that in every case the oil, or in that of cumarine the resinoid crystalline body, differs from the related acid only by 2 eqs. of oxygen. These oils and resinoid bodies are moreover fragrant (cumarine is the odorous principle of the tonka bean), and both they and the acids, especially the latter, approach to resins in properties, as well as in composition.
5. Volatile Oily and Fatty Acids, with the oils and fats containing them.
As the growing plant pushes its deoxidizing agency still further, fixed oils and fats are produced, a class of compounds both important and abundant. We already know their proximate constituents, namely, the acids of the formic or acetic series (excepting only the two acids lowest in the scale, which are not oily) on the one hand, and on the other the basic oxide of lipyle, or of glyceryle, or glycerine. It is unnecessary to repeat the list of acids, but we shall quote a few for illustration, with the oxide of lipyle.
| Oxide of lipyle (the base in fixed oils and fats) | C₃H₇O | | Glycerine | C₆H₁₀O₅ 2(C₃H₇O) + 3HO | | Butyric acid | C₄H₇O₄ | | Capric acid | C₁₀H₁₈O₄ | | Myristic acid | C₁₂H₂₄O₄ | | Cetyl and palmitic acids | C₁₆H₃₀O₄ | | Margaric acid | C₁₈H₃₄O₄ | | Oleic acid | C₁₈H₃₄O₄ | | Stearic acid | C₁₈H₃₄O₄ | | Cerotic acid | C₁₈H₃₄O₄ | | Melissic acid | C₁₈H₃₄O₄ |
We have already explained that fixed oils and fats consist of such acids as these, combined with oxide of lipyle, which, when the oil is saponified by boiling with potash or soda, separates in the shape of glycerine. The only exceptions yet known are those of spermaceti, which is composed of cetyllic acid, isomeric with palmitic acid, combined with oxide of cetylie, C₁₆H₃₀O, and wax, which consists partly of free cerotic acid, partly of palmitic acid combined with oxide of cetylie, C₁₆H₃₀O; and in some kinds of wax of melissic acid and oxide of melissyle, C₁₈H₃₄O. Drying oils, such as oil of linseed, of walnuts, &c., consist of oxide of lipyle, united to a peculiar oleic acid, which rapidly absorbs oxygen and dries up into a resinous mass or varnish. The neutral fixed oils and fats, composed as we have stated, are produced by a very high degree of deoxidation, when compared with the preceding groups, and are therefore formed in an advanced stage of the vegetative process. Hence they abound in seeds. In some of them, as in wax, the oxygen is reduced to a small fraction. But, taken as a whole, the group may be represented as sugar or starch minus oxygen, for sugar is C₁₂H₂₂O₁₁, and the average composition of fixed oils and fats is represented by the proportion C₁₇H₁₅O₅ or C₁₂H₂₂O₁₁. Hence, if fats are formed in the animal body from starch or sugar, as it seems certain they are, it must be by a process of deoxidation, although the general nature of the animal vital process is that of oxidation.
6. Resins and Camphors.
This group is small in point of numbers, but very abundant and widely diffused. In it the oxygen is still farther diminished, as may be seen in the following list.
| Many resins | C₁₀H₇O | | Camphor | C₁₀H₁₄O | | Borneo camphor | C₁₀H₁₄O | | Many resins | C₁₀H₁₄O | | Many acid resins | C₁₀H₁₄O |
Among these bodies isomerism and polymerism prevail Chemistry, to a great extent. The general character of the group is that they are very inflammable, fusible, insoluble in water, soluble in alcohol, frequently acid, but weak acids. Camphor is very volatile.
7. Non-oxygenated Volatile Oils.
In this group, which is both numerous and widely diffused, no oxygen is left. Isomerism and polymerism predominate among them, so that the following short list includes the most frequent proportions.
- Oil of lemons and various others: \( C_9 H_{16} \) - Oil of turpentine and various others: \( C_{10} H_{16} \) - Tolnaft: \( C_{12} H_{14} \) - Styrole or cinnamole: \( C_{10} H_{14} \) - Metastyrole or dracole: \( C_{12} H_{14} \) - Oil of juniper and others: \( C_{12} H_{14} \) - Cumene: \( C_{10} H_{14} \) - Cyrene: \( C_{10} H_{14} \)
Most of the volatile or essential oils of this class have a strong aromatic smell, and are indeed the source of the smell of the plants in which they occur. They are usually obtained by distilling the plants, flowers, seeds, or exudations from trees, with water, with the vapour of which the oils readily pass over. Many of them occur in the exudation from trees, especially from many of the conifers, mixed with resins, constituting what is called turpentine or balsam. When this is distilled with water the resin is left behind, and in this way common resin is obtained along with oil of turpentine, from the turpentine of commerce. Balsam of copaiva and Canada balsam are turpentines which, containing more oil, are more fluid. These oils, exposed to air, absorb oxygen, and dry up into a resinous mass. Indeed most resins in composition are the oxides of the volatile oils which occur with them. Hence the use of oil of turpentine as a varnish and in oil painting. True varnishes, however, are solutions of resins in oil of turpentine, alcohol, naphtha, pyroxic spirit, and other solvents.
The groups we have thus briefly sketched include all those vegetable compounds which consist of carbon, oxygen, and hydrogen only. But there are many and very important compounds which contain also nitrogen, and these we shall now endeavour briefly to indicate according to their natural affinities.
In order that these substances should be formed, the plant must be supplied with nitrogen, and this is done chiefly in the form of ammonia, or of nitric acid, both of which are conveyed to plants in the water which reaches their roots. In germination, however, there is another source of ammonia, namely, the decomposition of the albuminous or sanguigenous matter in the seed. Now it is remarkable that in germinating plants, before true leaves have been formed, and, what is the same thing, in etiolated plants, or those grown in the dark, the juice is found to contain a large proportion of a crystallizable nitrogenized compound, namely, malamide or asparagine. It would seem, therefore, as if this were the first nitrogenized body produced by the plant. Its origin is obvious. The plant first produces some acids, and among these malic acid. This meets with ammonia, and, water being separated, malamide is formed, or we may simply suppose it to be produced from carbonic acid, water, and ammonia. In the first case, malate of ammonia, \( C_4 H_5 O_4 \cdot 2 NH_3 \), losing 2 eqs. of water, yields malamide or asparagine, \( C_4 H_5 N_2 O_4 \). In the second, 8 eqs. of carbonic acid, 4 of water, and 2 of ammonia, yield 1 eq. of malamide and 12 of oxygen; so that, whether malic acid be first formed, or malamide be directly produced, if it be formed from carbonic acid, ammonia, and water, it must be by deoxidation, as in all the preceding groups. This is no doubt the case in growing plants where it occurs, but in germination it may be formed, at least in part, by the decomposition of fibrine, albumen, or caseine. All other compounds of amide, or those of imide, or, in short, all derived from ammonia, are formed in growing plants in the same way, that is by deoxidation. There are thus formed several classes of compounds, neutral amides, such as asparagine or malamide, amygdaline, and similar bodies, of which white or colourless indigo, the source of the coloured indigo, is one; the volatile bases, which may be either amide, imide, or nitryl bases; and the fixed bases, which are either ammonium bases, or coupled compounds containing such bases. The formation of the volatile and fixed bases in the various forms of amide, imide, nitryl, and ammonium bases, we have already explained in their proper place. We shall here unite in one short list a few nitrogenized vegetable compounds of the kinds we have mentioned, all of which are produced in plants, either directly from carbonic acid, ammonia, and water, by deoxidation, or indirectly from ammonia acting on substances already formed by deoxidation from carbonic acid and water, as we have explained above with reference to malamide.
| Compound | Formula | |-------------------|---------------| | Asparagine or malamide | \( C_4 H_5 N_2 O_4 \) | | White indigo | \( C_4 H_5 N_2 O_4 \) | | Amygdaline | \( C_4 H_5 N_2 O_4 \) | | Nicotine | \( C_4 H_5 N_2 O_4 \) | | (volatile bases) | \( C_4 H_5 N_2 O_4 \) | | Morphine | \( C_4 H_5 N_2 O_4 \) | | Quinine | \( C_4 H_5 N_2 O_4 \) | | Strecholine | \( C_4 H_5 N_2 O_4 \) | | Caffeine | \( C_4 H_5 N_2 O_4 \) |
This list will give an idea of the composition of the greater number of crystallizable or volatile nitrogenized products found in plants. The number of fixed bases is very large, but they all resemble those quoted, which are the active principles of the plants in which they occur; morphine of opium, where it is associated with several other bases, codeine, papaverine, narcotine, thebaine, and narceine; quinine of cinchona bark, which also yields cinchonine and quinidine, and strychnine of nux vomica, which also contains brucine. Besides these, there are veratrine in veratrum, atropine in belladonna, aconitine in aconite, digitaline in digitalis, datrine in datura, colchicine in colchicum, and others of less interest. Nicotine and cocaine, the active and very poisonous principles of tobacco and hemlock, are in all respects analogous to the volatile bases of the ethylie and benzoic series already noticed. Amygdaline is a bitter substance, peculiar to the bitter almond, which, in contact with water and the albuminous compound of the almond, undergoes a peculiar fermentation, and is resolved into several bodies not entirely known, but among them are hydrate of benzoyl and hydrocyanic acid, which together form the oil of bitter almonds of commerce.
White indigo is the substance present in the juice of indigofera, or at all events is produced by the action of ammonia on a substance there present, and as soon as it is formed, attracts oxygen, and is converted into indigo, \( C_4 H_5 N_2 O_4 \), the white indigo losing 1 eq. of hydrogen. Indigo, when acted on by different reagents, yields a large number of very interesting products of decomposition. With 2 eqs. of oxygen it forms isatine, \( C_4 H_5 N_2 O_4 \), and this yields a whole series of substitution products, in which chlorine and bromine are substituted for its hydrogen, besides many derivatives from these. When heated with potash, isatine yields carbonate of potash, hydrogen, and aniline, or phenylamine, \( C_4 H_5 N_2 O_4 \); so that the products of decomposition of indigo and its derivatives fall into the phenylie series. By the action of nitric acid, indigo is converted into two acids, according to the strength of the nitric acid. One of these belongs to the salicylic series, and is nitrosalicylic or indigotic acid, \( C_4 H_5 N_2 O_4 \); the other is a yellow, intensely bitter, crystallizable acid, which forms with potash a salt nearly indissoluble. It has been called carbazotic, picric, nitropic, and nitrophensic acid; but it is simply hy- Chemistry. drated oxide of phenyle, or carbolic acid, \( \text{C}_9\text{H}_8\text{O}_2\), in which 3 eqs. of hydrogen are replaced by 3 of nitrous acid, \( \text{C}_9\text{H}_8\text{NO}_3 \). This again connects indigo with the phenyl series. The same acid, which might perhaps be best named trinitrocarbolic acid, is formed in many other cases of the oxidation of organic compounds by nitric acid, as, for example, from aloes, and from several resins. But we can only indicate the existence of the numerous derivatives of indigo in this place.
Caffeine is found, not only in coffee, but also in tea; and in Paraguay tea or guarana, used for the same purpose as tea or coffee. It has considerable analogy in composition, and also in the products of its decomposition, with certain animal products connected with uric acid, and it is probably in virtue of this that it acts as a kind of stimulant.
There are one or two volatile oils, such as those of garlic and assafoetida, which contain sulphur. One, if not both of these, is sulphuret of allylic, \( \text{C}_4\text{H}_6\text{S} \); allylic being a radical either isomeric or identical with propionyl, the radical of propionic acid. Oil of mustard and oil of cochlearia are the sulphocyanide of allylic, \( \text{C}_4\text{H}_6\text{S}, \text{C}_4\text{N}_2\text{S}_2 \), and contain, therefore, both sulphur and nitrogen. In the formation of these oils in plants, carbonic acid, water, ammonia, and sulphuric acid are employed, and, as in all other cases, oxygen is given out.
There are various substances of no great importance which we have not specifically mentioned, but which all find their place in one or other of the groups of vegetable products we have named. Such are various colouring matters, and various volatile and crystallizable bodies, allied to the volatile oils.
But there remains one most important group of compounds formed by plants alone, and essential to the food of animals. This is the group of the albuminous or sanguigenous bodies, the only substances from which the animal system can form blood. These are three in number—albumen, fibrine, and caseine; and they are all of vegetable products the most complex, containing not only the five elements already mentioned (carbon, hydrogen, nitrogen, oxygen, and sulphur), but also—as essential constituents, without which, though in small proportion, they cannot even exist—mineral salts, especially phosphates. Moreover, the number of atoms in these compounds is far larger than in any we have mentioned, amounting, indeed, to hundreds. It is evident that one chief object of vegetation is the formation of these substances, and also that from their complexity they must be the last formed; and in fact they abound in the seeds, tubers, and other parts capable of reproducing the plant, and after the formation of which the plant dies down, either for a season or permanently. They are always accompanied by the two other classes of compounds, which with these constitute not only the first food of the young plant, but the food of animals, namely, starch, sugar, gum, or cellulose, on the one hand, or oils and fats on the other; these two constituting the respiratory part of animal food, as the three more complex products constitute the sanguigenous part of that food.
We may either conceive these compounds to be formed directly from carbonic acid, water, ammonia, and sulphuric acid, with the separation of oxygen; or, what is much more probable, we may suppose them formed from compounds already of a certain degree of complexity, such as sugar, with the aid of ammonia and sulphuric acid, or finally from sugar or some such substance, acted on by some nitrogenized compound, such as malamide. The precise steps of the process are unknown, but it is obvious that, whether formed directly or indirectly, they must be ultimately derived from the original food of plants—carbonic acid, water, ammonia, sulphuric acid, and the mineral salts derived from the soil—and that this cannot take place without the separation of a large amount of oxygen. The nearest approach we can make to the formulae of these compounds is the following:
\[ \begin{align*} \text{Albumen and fibrine} & : \quad \text{C}_{12}\text{H}_{22}\text{N}_2\text{O}_5 \\ \text{Caseine} & : \quad \text{C}_{12}\text{H}_{22}\text{N}_2\text{O}_5 \end{align*} \]
besides the phosphates. It is very difficult to ascertain with certainty such formulae; but these, with respect to the proportions, represent the results of analysis; and as to the absolute number of atoms, we assume 2 eqs. of sulphur, because we find that these bodies contain sulphur in two different states, which implies at least 2 atoms.
These substances are essential to the growth of plants, as the vegetable cell, even if formed of cellulose alone, cannot be formed without the presence of one of these bodies. But in fact they also take part frequently in the formation of the cell wall, and the primordial utricle, or lining membrane of the cell, seems to consist chiefly of them.
Vegetable fibrine and albumen are isomeric; or, at least, the best analyses have not been able to show more difference between them than between different analyses of one of them. When dissolved in the vegetable juices, the fibrine coagulates spontaneously, the albumen when the liquid is boiled, and the caseine on the addition of an acid after the coagulation of the albumen, if all three or two of them be present together. In the solid form they are found, fibrine in the seeds of grasses and cerealia, albumen in those of nuts, almonds, and the kernels of stone fruit; and caseine in the seeds of the leguminosae. The fibrine in grain is accompanied by starch and a little sugar, and in some cases also a little oil; the albumen is almost always associated with oil, as in almonds, walnuts, hazelnuts, and many other seeds; and in the seeds of leguminosae the caseine is mixed chiefly with starch. In edible roots and tubers there is the same mixture. In the potato, fibrine and starch; in carrots, turnips, &c., fibrine, sugar and pectine; in pulpy fruits, fibrine, starch, sugar, and pectine, are the chief ingredients. In short, the vegetable cannot live and grow, and bear fertile seeds, without at the same time providing food for animals, not only in seeds, roots, and tubers, but also in leaves, leaf-stalks, leaf-buds, flower-buds; and, indeed, every part which is full of juice. And this leads us to consider the composition of the animal body.
But first we must remind the reader, that we have seen that plants live on carbonic acid, water, ammonia, sulphuric acid (in the form of sulphates), and phosphates, chlorides, alkalies, and other mineral matters—the three first compounds derived from the air, the rest from the soil. Secondly, that in germination, which takes place in the dark, oxygen is absorbed along with water, the albuminous matter in the seeds enters into decomposition, and becomes a ferment, by which means the starch is converted into sugar and dissolved, along with the greater part of the albumen, which is also rendered soluble by the fermentative action of the decomposed portion, while malamide appears, probably derived from the same source, and carbonic acid is given out. And thirdly, that as soon as the first leaves are formed, and light obtains access, the true, proper, vegetative process begins, in which, from the articles of their food above enumerated, plants produce acids, neutral substances, mild or acid, or bitter or coloured, bases, oils and fats, resins, volatile oils and volatile acids; and finally, sanguigenous compounds, the formation of all of these being dependent on light, and being accompanied by the continual evolution of oxygen. Such is the nature of the vegetative process, carried on in virtue of the energy derived from the solar rays, and it is marked by three essential characters; the first is, that light is absolutely essential to it; the second is, that it is essentially a constructive process, in which the least complex compounds forming the food of plants are built up into more and more complex forms, till at last the sanguigenous bodies, the most complex of all, are produced; and the third, that it is a process of deoxidation of the food. Chemistry of plants to a greater or less extent, and occasionally complete; but a deoxidation of a kind unknown in the laboratory, where we can only deprive bodies of oxygen by using others which seize and retain the oxygen, whereas the plant retains the carbon, hydrogen, and nitrogen, &c., and liberates the oxygen. The power required for this must be prodigiously great, and must far surpass that of our most energetic agencies; yet the vegetable cell effects it, without the help either of heat or of any other appliance. There can be no doubt that light is the source of this astonishing power; but, be this as it may, it is characteristic of vegetation.
Let us now turn to the animal system. We have stated that the food of animals is composed of two kinds of substance, the sanguigenous, and the respiratory. Both must be rendered soluble in order that they may enter the circulation, and this is effected in the process of digestion. It is remarkable, that this first animal process agrees with the first vegetable one, namely, with germination. In mastication, the food is divided and mixed with saliva, oxygen being added from the air, and being inclosed by the viscosity of the saliva. In the stomach, the gastric juice is added, which contains a little free acid, some albuminous matter dissolved, and the usual animal salts. The dissolved albuminous matter, acting as a ferment, at the temperature of the body, renders the sanguigenous portion of the food soluble, while either the same ferment, or, as is now believed, one peculiar to the saliva, converts the starch, if any be present, into sugar, so that it also is dissolved. The dissolved sanguigenous matter is gradually converted into blood, and from that fluid the various tissues are formed. The fibrine of flesh and the albumen of the blood are identical with vegetable fibrine and albumen; but the fibrine of the blood and the albumen of eggs are different. The two former, as we have already stated, are $\text{C}_{25} \text{H}_{38} \text{N}_{2} \text{S}_{2} \text{O}_{16}$. Now, when one of them is employed to produce blood fibrine, or hematofibrine, which is $\text{C}_{25} \text{H}_{38} \text{N}_{2} \text{S}_{2} \text{O}_{16}$, it may be in this manner that 2 eqs. albumen (or fibrine) with 2 eqs. of water are converted into 1 of hematofibrine, 1 of gelatine, $\text{C}_{25} \text{H}_{38} \text{N}_{2} \text{O}_{16}$, and 1 of cholic acid, one of the acids of bile, $\text{C}_{25} \text{H}_{38} \text{NS}_{2} \text{O}_{14}$. Or it may be that 2 eqs. albumen and 4 of water yield 1 eq. hematofibrine, 1 gelatine, 1 cholic acid, the other acid of bile, $\text{C}_{25} \text{H}_{38} \text{NO}_{12}$, and 2 of sulphuric acid. Lastly, these two processes may be combined, so that—
\[ \begin{align*} 4 \text{ eqs. albumen} & \quad \text{yield} \quad 2 \text{ eqs. hematofibrine.} \\ 6 \text{ eqs. water} & \quad \text{yield} \quad 2 \text{ eqs. gelatine.} \\ & \quad \text{yield} \quad 1 \text{ eq. cholic acid.} \\ & \quad \text{yield} \quad 2 \text{ eqs. sulphuric acid.} \end{align*} \]
By this it will be seen that the formation of blood fibrine is accompanied most probably by that of gelatine, necessary for membranes and bones, and that of the chief constituents of bile. Indeed, blood fibrine may be regarded as ordinary fibrine and albumen, half converted into gelatine and bile, for 1 eq. of it with 18 of water, may yield 3 of gelatine and 1 of cholic acid.
This example will illustrate the fact, that while the animal body cannot produce any sanguigenous body from food in which none of them is present, it can transform one into the other, as albumen into fibrine, fibrine into albumen, or both into caseine, or, as we have just seen, albumen or fibrine into hematofibrine; but that, where such changes are not isomeric transformations, they are a commencement of destruction, and their production, even if more complex, as is the case with hematofibrine, is not a pure case of construction as in the plant, but one in which with one more complex body others much less complex are produced. In the same way, when the food contains caseine, as milk does, and when hematofibrine is formed from caseine, it is accompanied by the production of chondrine, the substance of which cartilage, so necessary to the young animal, is formed.
In this way, then, the animal body, if supplied with albumen, fibrine, or caseine, can produce from them, or any one of them, the materials necessary, in addition to themselves, for the formation of blood, muscular fibre, membranes, cartilage, bones, &c., even although these should be in part more complex than the food. But it is beyond the power of the animal body to produce any one of these substances from food which does not contain at least one of them, and for that food it is absolutely dependent on vegetables. Although we do not know the details, there can be no doubt that the formation of nervous matter or cerebral substance, is effected on the same principles. In this stage, water, as we have seen, is taken up, but oxygen is not required, nor is it given out. It is after the formation of blood and of the tissues, by some such changes as those we have specified, that the true vital process peculiar to animals begins. This process is exactly the reverse of the vegetative one; for while the latter, acting by deoxidation of the least complex among compounds which are its food, constructs or builds up those that are more and more complex, till it produces the most complex of all, that is, the food of animals, giving out during the whole succession of changes a large amount of oxygen; the former takes up, in respiration, a large amount of oxygen, acts by oxidation, and beginning with the most complex compounds, destroys them, and breaks them up into such as are less and less complex, ending at last with the very same substances as form the food of plants, and giving out all the time, in respiration, carbonic acid, in quantity equal, or very nearly so, to the oxygen absorbed, the difference of oxygen being given out as water.
These two great processes are exactly opposed, and, in point of fact, exactly balance each other, so that the air remains always of the same composition, although animals are constantly removing oxygen and replacing it by carbonic acid, because plants, on the other hand, are constantly removing carbonic acid, and replacing it with oxygen.
As to the products of the oxidation and destruction of the tissues in the animal body, they are very numerous, and only partially known. Such bodies as gelatine, chondrine, and the like, are among them, and it is to be observed that these products of destruction of the tissues, even when they approach in complexity the sanguigenous bodies, are not capable of forming blood. Thus gelatine alone can never support animal life, not being convertible into blood, as fibrine, albumen, and caseine are.
After such complex products of oxidation as gelatine and chondrine, there come probably a number of intermediate compounds, which, however, are as yet unknown. But at a certain stage in the oxidizing process bile is formed, which is composed of the two acids, cholic acid $\text{C}_{25} \text{H}_{38} \text{NS}_{2} \text{O}_{14}$, and cholic acid $\text{C}_{25} \text{H}_{38} \text{NO}_{12}$, both combined with soda. We have already noticed these acids under the series of glycine, which may be formed from cholic acid, while taurine, a compound containing all the sulphur of the bile, is obtained from cholic acid. In both acids, these substances are coupled with cholalic acid, $\text{C}_{25} \text{H}_{38} \text{O}_{19} = \text{C}_{25} \text{H}_{38} \text{O}_{19}$. HO.
Anhydrous cholalic acid $\text{C}_{25} \text{H}_{38} \text{O}_{19}$
Anhydrous glycocine $\text{C}_{25} \text{H}_{38} \text{NO}_{12}$
Cholic acid $\text{C}_{25} \text{H}_{38} \text{NO}_{12}$
Anhydrous cholalic acid $\text{C}_{25} \text{H}_{38} \text{O}_{19}$
Anhydrous taurine $\text{C}_{25} \text{H}_{38} \text{NS}_{2} \text{O}_{14}$
Cholele acid $\text{C}_{25} \text{H}_{38} \text{NS}_{2} \text{O}_{14}$
Cholalic acid, by boiling with water, is converted into a resinous acid, isomeric with the anhydrous cholalic acid, which is called cholotic acid; and when this is further boiled with acids, it yields a very insoluble resin, called dyslysine, which is cholotic acid minus 3 eqs. of water, or $\text{C}_{25} \text{H}_{38} \text{O}_{19}$. Such are the chief products of bile. It is probable that all the sulphur of the tissues takes the form of cholic acid, that is, passes into the bile, before being expelled from the body as sulphuric acid by farther oxidation. The bile, which is mixed with the digested mass of food as it leaves the stomach, is apparently reabsorbed after producing some important effect in digestion, or in the conversion of the food into perfect chyle or blood, and being thus thrown into the circulation, it is destroyed by oxidation. We have already seen how the acids of bile may be formed from albumen or fibrine, along with hematothrine, and also from the latter body by the addition of water; but they are also formed by oxidation.
For example:
\[ \begin{align*} 1 \text{ eq. albumen}, & \quad 6 \text{ eqs. cholic acid}, \\ 10 \text{ eqs. water, and} & \quad 2 \text{ eqs. cholic acid}, \\ 56 \text{ eqs. oxygen,} & \quad 12 \text{ eqs. urea}, \\ & \quad 36 \text{ eqs. carbonic acid}. \end{align*} \]
Or cholic acid may be formed, beside various other processes of oxidation, from chondrine and gelatine, as follows:
\[ \begin{align*} 1 \text{ eq. chondrine by} & \quad 1 \text{ eq. cholic acid}, \\ \text{a fermentation, probably} & \quad 2 \text{ eqs. uric acid}, \\ & \quad 8 \text{ eqs. water}. \end{align*} \]
\[ \begin{align*} 1 \text{ eq. gelatine, with} & \quad 1 \text{ eq. cholic acid}, \\ 10 \text{ eqs. water,} & \quad 3 \text{ eqs. uric acid}, \\ & \quad 12 \text{ eqs. water}. \end{align*} \]
In all these three examples, it will be seen that the biliary products are accompanied by such as are urinary, urea, uric acid, and water, and also by carbonic acid. There are, no doubt, many other modes of decomposition and intermediate products, and some of these products we know, as for example, creatine \(C_8H_{14}N_2O_4\) and hippuric acid \(C_{18}H_{22}NO_9\), the former being found in the juice of muscle and in urine, the latter in urine. Now we can easily see how they may be formed, from gelatine for example, for—
\[ \begin{align*} 1 \text{ eq. gelatine, and} & \quad 3 \text{ eqs. creatine}, \\ 58 \text{ eqs. oxygen,} & \quad 2 \text{ eqs. hippuric acid}, \\ & \quad 12 \text{ eqs. water}, \\ & \quad 22 \text{ eqs. carbonic acid}. \end{align*} \]
Any of these substances, fully oxidized, will yield carbonic acid, ammonia, water, and, if sulphur be present, sulphuric acid. Thus—
\[ \begin{align*} 1 \text{ eq. of cholic acid, and} & \quad 1 \text{ eq. ammonia}, \\ 144 \text{ eqs. oxygen,} & \quad 2 \text{ eqs. sulphuric acid}, \\ & \quad 52 \text{ eqs. carbonic acid}, \\ & \quad 42 \text{ eqs. water}. \end{align*} \]
When uric acid is formed, it must, in warm blooded animals, be farther oxidized, so as to yield soluble compounds, or else by its insolubility it is deposited, producing calculous disease. In general, all the uric acid but a very small portion is thus oxidized, and the results are (uric acid = \(C_{10}H_4N_2O_2\))—
\[ \begin{align*} 1 \text{ eq. uric acid,} & \quad 2 \text{ eqs. oxalic acid}, \\ 3 \text{ eqs. water,} & \quad 1 \text{ eq. urea}, \\ 2 \text{ eqs. oxygen,} & \quad 1 \text{ eq. allantoin}. \end{align*} \]
or
\[ \begin{align*} 1 \text{ eq. uric acid,} & \quad 4 \text{ ammonia}, \\ 8 \text{ eqs. water,} & \quad 2 \text{ urea}, \\ 6 \text{ eqs. oxygen,} & \quad 10 \text{ carbonic acid}, \end{align*} \]
or
\[ \begin{align*} & \quad 4 \text{ water}, \\ & \quad 3 \text{ carbonic acid}. \end{align*} \]
It will be seen that the less complete oxidation of uric acid produces, besides urea, oxalic acid and allantoin. Oxalic acid does occur, and when it meets with lime is apt to form a calculus of the insoluble oxalate of lime. Allantoin is found in the allantoic fluid or foetal urine, and in the urine of very young animals, in whom respiration, and consequently oxidation, is somewhat imperfect. But when the oxidation is complete, urea or ammonia, carbonic acid, and water, are the products.
Many more examples might be given of the mode in which the changes in the animal body may be supposed to be effected, and in some such modes they must be effected. But as we do not know all the different stages of the oxidation, nor all the products, we only give these representations as possible or probable, in regard to the details, although in principle certain; for all the facts we know prove that in the animal body every change is the result either of oxidation, more or less complete, or of a transformation with or without the addition of water, but never, as in plants, of deoxidation with liberation of oxygen. On the contrary, oxygen is constantly absorbed, carbonic acid constantly given out, and the complex substance of the tissues is constantly broken up into less and less complex compounds, till the final result is the food of plants.
It is in the very performance of their proper functions that the tissues are oxidized, and as fast as a portion of any tissue being oxidized, is, while doing its work, broken up, the blood replaces it by a new portion derived from the food. At the same time the blood carries off the broken up or effete tissues, and out of them produces, according as the oxidation is more or less advanced, gelatine and the like, bile, juice of muscle, or urine. It is the blood which conveys to every part the oxygen necessary for the destruction of the tissues, that is, for the performance of their functions, which is their destruction. This is the reason why great efforts of any kind, muscular or otherwise, are attended with great waste of substance, and require an increased supply of food. It is the blood also, which, after it has carried the oxygen to act on the tissues, so as to enable them to perform their part, and in so doing to be destroyed, pro tanto; and after it has replaced the effete tissues which have, in becoming effete, fulfilled their office, by fresh material, also carries away not only the solid and liquid products of oxidation, but also the carbonic acid so largely formed, which it conveys to the lungs, and there exchanges for oxygen. But there is another source of carbonic acid besides the oxidation of the tissues. This is the oxidation or slow combustion of the respiratory food, of the sugar, &c., and the oils or fats, some of which are always present in food, as provided by Nature. And it is by this oxidation of the carbon and hydrogen of these matters as well as those of the tissues that the animal heat is kept up, without which none of the vital processes could be carried on. Now both the oxygen required for this purpose and the carbonic acid produced are carried to and fro by the blood, which at the same time has to perform three most essential functions, or rather four; first to enable the tissues, by oxidizing them, to perform their functions; secondly, to repair the waste of tissue; thirdly, to concoct or assist in concocting, out of the first products of oxidation, the various secretions and excretions; and lastly, to effect by the oxygen it carries the oxidation also of the respiratory food, or the production of animal heat, and to convey to the lungs the carbonic acid which is formed, and exchange it for oxygen.
The blood is admirably fitted for these purposes. It consists of water, holding in solution, besides salts, albumen and fibrine, and in this solution are suspended the red and white blood corpuscles. These seem to have much to do in the conveyance of the gases, which probably adhere to them. At all events, their colour changes from dark to bright red, according as the blood is loaded with carbonic acid (venous), or with oxygen (arterial). But that the blood may absorb so much carbonic acid, and yet give it out easily, it must be alkaline, and yet not too alkaline, which would retain the carbonic acid. This is accomplished by the presence of the peculiar phosphate of soda, tribasic with 2 eqs. of soda, which, acid in composition, is alkaline in character; namely, \(P_2O_5\), \(2NaO.H_2O\). It absorbs carbonic acid as well as carbonate of soda, and gives it off much more readily and completely. For another reason, the blood must be alkaline; for if it were acid, or even neutral, neither fibrine nor albumen could remain dissolved, nor could the necessary changes take place. Moreover, it must be phosphate of soda in the blood, and not that Chemistry. of potash, for potash tends to form the salt $\text{PO}_4 \cdot \text{K}_2\text{O} \cdot 2\text{H}_2\text{O}$, which is an acid salt. This very salt exists in the juice of muscle, which is almost in absolute contact with the blood, and in the gastric juice, but never in the blood, though the fluids which contain it are only separated from it by the most delicate possible membrane. The presence of these two fluids, blood and juice of muscle, one alkaline, the other neutral or slightly acid, in such close proximity, is probably connected with the existence of currents of electricity in the body, which have been demonstrated especially in muscular action. Two such fluids, with a porous solid between them, will always create an electric current.
It is obvious that for two chief reasons the supply of oxygen to the animal body must be abundant. It has to oxidize and destroy the tissues, that is, to enable them to perform their functions; and it also has to consume the respiratory food, and ensure the regular supply of animal heat. The effects of a deficient supply of oxygen are easily seen. The tissues being less thoroughly oxidized, the blood must become loaded with intermediate products. Among others, uric acid must occur, and give rise to calculous and gouty diseases. And this is the case. But deficiency of oxygen may arise from two causes: either from an absolute defect of oxygen, from diminished respiration, sedentary habits, which diminish respiration, and other analogous causes, or, what is more common, excess in food, whereby a full ordinary supply of oxygen becomes insufficient. This is the principal reason why excess in eating causes disease. Another cause may contribute to this, namely the deficiency of alkaline salts in the food, which is apt to occur if too much animal food and too little vegetable food be taken. The alkaline salts of vegetable acids are converted into carbonates in the system, and the presence of these greatly promotes oxidation; hence their absence or deficiency is injurious. For the same reasons, the strong wines of the south, which contain hardly any tartar, that is, acid tartrate of potash, are apt to cause calculus and gout, if habitually used; while on the Rhine, where wine is the only beverage, but the wines are weaker, and strongly charged with tartar, these diseases are unknown, save as imported.
When from any cause the supply of oxygen in proportion to the sanguigenous food is too small, the animal body possesses the singular power of obtaining a supply of oxygen from sugar or starch, which, by losing oxygen, are converted into fat. In this way the animal body can produce fat from sugar, like the plant, but the oxygen, instead of being given out, is employed to make up for the deficiency of that element. At the same time, as fat is formed along with it, the animal becomes fat. This explains why stall-fed animals fatten sooner than such as are outside; the former having a deficient supply of oxygen, that is, deficient respiration, compared with the latter; it also explains how the most fattening food is such as contains, with a certain proportion of sanguigenous matter, a large amount of starch or sugar. In this point, the practice of experienced feeders is entirely according to theory.
The food of animals and of man must contain a due proportion of sanguigenous and respiratory matter. For man, the best proportion is that found in grain and in milk, which are almost the only articles of food on which, alone, that is, on either of them without addition, life and health can be sustained. In them, the proportion is 1 part of sanguigenous matter to $4\frac{1}{2}$ or 5 of respiratory matter. Lean meat contains too little respiratory matter, although it contains a good deal of fat or oil diffused through it. Pease and beans and cheese are also too rich in sanguigenous matter, while potatoes and rice contain a great excess of respiratory food, which is the case also with very fat meat, such as bacon, &c. Hence, we usually add potatoes or rice to lean meat, and bacon or fat pork to pease and beans. Working men fed on potatoes require a very large supply of that food, so poor in sanguigenous matter, for it contains but 1 part of fibrine Chemistry, to 8, 10, or 11 of starch, to supply the daily waste of tissue, which starch cannot supply. With a large amount of potatoes they may thrive, but in that case much starch passes off unchanged in the excreta. On the other hand, when men are fed exclusively on flesh, they require a very large supply of it, as do carnivorous animals, because, besides supplying the waste of tissue, a large part has to be oxidized to yield the animal heat, for which it is far less fitted than starch. To burn off, or oxidize, so much sanguigenous matter requires a very large supply of oxygen, and this is the reason why carnivorous savages must lead a life of continual exertion, as they generally do in hunting for their food. For the same reason, carnivorous animals in confinement are always in motion except when asleep. The exercise increases the frequency and depth of respiration, and thus promotes oxidation. Lastly, the respiratory food is required, not merely to yield animal heat by its slow combustion, but also to yield fat by its deoxidation, which fat or oil assists in the formation of tissues from sanguigenous matter.
Such, in a very few words, are the general laws which regulate the food of animals. As to the excreta, they consist, for the most part, of the gases and vapours formed by oxidation, or carbonic acid and water, excreted by the lungs and skin, and ammonia, chiefly excreted in the form of salts in the urine; of the soluble salts which have served their purpose in the economy, or are the result of oxidation, as phosphates of potash, soda, and ammonia, sulphates, chlorides of potassium and sodium, &c.; of soluble organic excreta, as urea and creatine, with traces, in man, of uric and hippuric acids, which, with the soluble salts and other less known substances, are excreted in the urine; and, finally, of the insoluble salts, as phosphates of lime, magnesia, and iron, along with any undissolved or insoluble matter in the food, as woody fibre, excess of starch, resinous matters, and certain fetid products of the oxidation of sanguigenous bodies which are also insoluble, but have not been fully studied, all of which insoluble matters form, with a certain amount of water, the solid or semisolid excreta. In cold-blooded animals, such as reptiles, where oxidation is very imperfect, there is no liquid urine; the whole excreta form one mass, which, in serpents for example, consists partly of undigested matters, bones, hair, feathers, and the like, but chiefly of a white salt, urate of ammonia. The same is true, to a great extent, of carnivorous birds, such as sea fowl, whose excreta consist of the bones of fishes and urate of ammonia. Exposed to the air, they became partly altered, the uric acid being in part converted into oxalic acid and other products, and the result is guano, which owes its value as a manure to the phosphates it contains, to the salts of ammonia, and to the uric acid, which is a source of ammonia when further decomposed.
We have seen that the animal process is the reverse of the vegetable one; that it begins where the other ends, with the sanguigenous and respiratory substances, and ends where the other begins, in the excreta, gaseous, liquid, and solid, which amount to carbonic acid, ammonia, water, sulphuric acid, or sulphates, phosphates, chlorides, &c., in short, the very substances which are the food of plants. Urea, on being expelled in the urine, is soon transformed into carbonic acid and ammonia; for $\text{C}_2\text{H}_4\text{N}_2\text{O}_2 + 2\text{H}_2\text{O} = 2(\text{NH}_3, \text{CO}_2)$. This change takes place under the influence of a ferment, and the ferment in the urine is the mucus suspended in it; for if this be at once separated by filtration, the urea does not ferment.
We have noticed the composition of the best known among the constituents of the animal body, and the products of the various changes which occur during life. The various secretions are formed chiefly of water, with certain animal substances dissolved, generally in small quantity, and Chemistry, certain salts. Milk, which is important as a naturally prepared food, adapted more especially to the growth of the young animal, contains a considerable amount of caseine dissolved, which is identical with the caseine of peas, beans, and other leguminous plants. The respiratory food in milk consists of fat or oil, called butter, which we have already described under the head of the volatile oily acids of the acetic series, and of a peculiar form of sugar, called lactine or sugar of milk, the composition of which is $C_{12}H_{22}O_{11}$, the same as that of dry grape sugar, with which, however, it is only isomeric, not identical.
When milk is left to itself, the oil rises to the surface as cream. But soon after, the caseine enters into decomposition, becomes a ferment, and induces in the sugar the lactic fermentation, by which lactic acid is formed. This goes on till so much free acid is formed as checks the fermentation; which is, however, immediately renewed if the acid be neutralized by soda or chalk. The coagulation of the caseine instantly follows the formation of lactic acid, that is, as soon as the alkaline reaction proper to milk is neutralized, and it becomes distinctly acid. This is why milk when sour is found coagulated. The other method of coagulating milk, by means of rennet, an infusion of the lining membrane of the calf's stomach, depends on the dissolved sanguigenous matter in the rennet acting as a ferment, and coagulating the caseine rather by an action of contact, as it converts starch into sugar, than by the formation of lactic acid, for the coagulation by rennet is complete before the milk becomes perceptibly acid. The whey or serum, separated from the curd, contains all the sugar, various salts, especially phosphate of potash, and a small quantity of an albuminous matter not fully studied.
Cheese is the coagulated caseine, more or less perfectly separated from the whey, and containing more or less of the oil or butter, according as made from cream, from milk as drawn, or from skimmed milk, when only traces of oil are left. The different flavours and qualities of cheese also depend in part on the pastures, in part on the mode of manufacture followed in different places.
The gastric juice has been mentioned as resembling the juice of muscle, in being acid from the acid phosphate of potash, $PO_4$, KO, $2H_2O$. Its power of dissolving fibrine, albumen, &c., depends on its being acid, and on the presence of a ferment, or dissolved sanguigenous matter in a state of decomposition. We can imitate this solvent action out of the body by placing flesh in a solution of 1 part of hydrochloric acid in 1000 of water at the temperature of the body. A small part of the flesh, or of some of the membranes about it, is first dissolved, and by degrees the whole is softened and converted into chyme, in which the greater part of the fibrine is dissolved, and the oil suspended, giving it a milky aspect.
The pancreatic juice seems to have a special action in rendering fats and oils soluble, or at least capable of being absorbed. It is said to set free the acids which are more soluble than the fats themselves. Its composition is not perfectly known, but it resembles that of the saliva, which, as we have seen, is supposed to be the special agent in the conversion of starch into sugar. The bile and the urine we have already described. The latter is a solution of urea with salts, and certain little known products of the changes in the body, which are commonly grouped together as the extractive matter, besides traces of krea line, creatinine, a base differing from creatine in containing 4 eqs. of water less, hippuric acid, and uric acid. In the extractive matter of cow's urine there have been found a substance, tauric acid, very analogous to, and probably homologous with, carbolic acid, also carbolic acid itself, and two other acids, both volatile and resembling carbolic acid. Carbolic acid is $C_{6}H_{5}O_{2}$, tauric acid $C_{7}H_{8}O_{3}$, damaric acid is $C_{14}H_{12}O_{4}$, and damaric acid $C_{26}H_{22}O_{4}$. All these are, like carbolic acid, which occurs in tar, products of incomplete oxidation Chemistry, or combustion, as tar itself is; and their occurrence is a strong illustration in favour of the view which regards the body as a furnace, in which the food is the fuel, the carbonic acid, water, and ammonia are the products of complete combustion, and the soot and ashes combined are represented by the solid and liquid excreta.
The juice of muscle or of flesh is remarkable for being either neutral or acid, although in close proximity to the alkaline blood with only a thin and permeable membrane between them; also for containing potash where blood contains soda; and for the occurrence of creatine in much greater quantity than in the urine. It also contains albumen, coagulable by heat.
Uric acid has been much studied, in reference chiefly to its products when oxidized. It yields a very large number of remarkable derivatives, but for the present these, although interesting to the chemist, do not admit of any application so important as to render it necessary to detail them here. We have stated what the most practically important results of its more or less complete oxidation are, and in the human body it is only a trace of it which, from its sparing solubility, can enter the urine, the rest being converted into urea chiefly with allantoin and oxalic acid in one case, and in the more frequent one, carbonic acid and water, or carbonic acid and ammonia.
Now that we have traced the two great processes of organized life, the vegetable and animal, and have seen how they are mutually related, and how they balance, and are dependent on each other, we can easily understand the principles which ought to regulate agriculture. Vegetation is entirely a chemical process, and subject therefore to chemical laws, although the vital force which modifies their action be beyond our reach. The plants, as we have shown, nay, the single cell, can effect changes which are beyond the power of the chemist, with all his appliances of heat, electricity, and chemical agents. But still these are chemical changes. If, then, vegetation be a chemical process, the foundation of a rational agriculture must be laid in chemistry.
Now the food of plants consists of two parts, the atmospheric and the terrestrial. The former is but little in our power, and therefore it is to the latter, that is, to the soil, that we must direct our attention.
We have already specified those elements which the plant derives from the soil, and which are fortunately present in almost every soil. They are sulphur, in the form of gypsum, phosphates of lime and magnesia, oxide of iron, carbonate of lime, potash, soda, silicic acid, and in some cases iodides and fluorides. But some of the most essential, especially the phosphates, are often present in so small a proportion as not to suffice for the purposes of agriculture.
The first principle that may be laid down is this, that to render a soil generally fertile, all the mineral substances which are really essential to the crops must be present, and in sufficient quantity. The absence of one essential ingredient renders the others, however abundant, totally useless. No plant can grow in a soil destitute of phosphates, or of sulphates, or of alkalies. Some plants may grow, indeed, in the absence of one important mineral element, as, for example, of potash, but only on condition that some other analogous substance, such as soda in some cases, and lime in others, replaces it. There is no means of remedying the absence of phosphates or of sulphates, because nothing else can replace them.
The next point to be noticed is, that the crops raised for food in agriculture exhaust the soil of certain constituents to a far greater extent than any natural vegetation can do. In all cultivated plants, the edible part, whether seeds, roots, or leaves, has been brought to a most unnatural development, for the sake of the food they yield. Now, a great Chemistry, part, and the most valuable part of that food consists of sanguigenous matter; and this, as we have already stated, cannot exist without a certain amount of phosphates of lime and magnesia. There is no such thing known as albumen, fibrine, or caseine, without phosphates. Now of all the useful constituents of the soil, the phosphates are the least abundant, so that in many cases a cultivated crop or two exhausts the soil of all its available phosphates. The same thing is true of any other constituent required for the cultivated crop and not very abundant in the soil.
The next principle is this, that if the soil by nature can produce an average cultivated crop, this degree of fertility can only be kept up in one way, that is, by restoring to the soil exactly what we have removed of mineral matter in the crop. For this is another difference between natural vegetation and cultivated crops; that in the latter case a great part of the crop, and that by far the richest in mineral matter, especially in phosphates, is exported or abstracted from the land. This is the principle on which the use of manures depends, for manures are nothing but different means of restoring to the soil what we have extracted from it.
The next remark we would make is, that common or farm-yard manure is evidently, from its origin, a most excellent form of manure; for, consisting of straw which is part of the crop, and of the solid and liquid excreta of animals fed on another part of it, the latter, as we have explained, represent the ashes of that part of the crop on which the animals have fed. But the ashes of any crop are exactly the mineral substances which it required and extracted from the soil, and in the very proportions required; so that the ashes of any crop must be the best manure for another crop of the same, provided the first crop was a good one.
Unfortunately only a part of the crop is consumed on the spot and converted into manure, and therefore the farmer must have recourse to other modes of restoring what has been removed, or of supplying what may be deficient.
The most natural quarter to which he can apply is the excreta of large town populations, both of men and of animals, which have consumed that part of his crops which was exported. But hitherto this invaluable manure has been, for the most part, carefully washed down into the sea, and thus lost for ever to the land, except in so far as a part of it is recovered, at a most disproportionate cost, in the shape of sea-ware, and still more of guano. For the town manure, conveyed into the sea, there promotes the growth of sea plants of all kinds; on these small animals feed; on these again fish; on these larger fish, and on these perhaps sea-fowl, whose excreta, after ages of exposure, are imported as the most precious manure, while at the same moment we are recklessly casting away the very best manure for our crops, being the ashes or mineral part of these crops, contained in the excreta of towns.
Another manure, imported also at great cost, and like guano very likely to fail us ere long, is bones or bone dust. As we have already said of guano, in speaking of uric acid, that its value chiefly depends on the phosphates it contains, so is the value of bones measured by the phosphates. But the animals whose bones we purchase feed on our crops, or on others similar to ours, and every particle of phosphate in them has been extracted from the soil in these crops. In bones, therefore, we are only restoring, as in guano, at great cost, a part of what we have removed from the soil. And what we gain in bones is lost to the countries exporting them.
In short, every particle of manure ought to be carefully preserved, whether on the farm, or in large cities where it is now thrown away to the value of millions annually. Experience and observation have taught this truth long ago to the Chinese, who do not allow the smallest portion of that to be wasted which has been extracted from the soil; and yet probably they have no theory, no science to guide them. When shall we, who can see why this ought to be done, act with the same common sense as the Chinese have long Chemistry exhibited?
Besides the phosphates, for the sake of which farm-yard manure, guano, and bone-dust are chiefly valued, there are other substances which must be restored to the soil. Sulphate of lime or gypsum is fortunately present in considerable proportion in most soils, but where it is deficient one crop may exhaust the soil of it. It is easily obtained, being a common rock, or mineral.
The alkalis, although almost always present in considerable proportion, are yet apt to fail, because it is only that portion which is soluble that can avail the plant. Now the potash is all derived from felspar, but felspar is quite insoluble, and it is only in so far as it is decomposed that it yields its potash. This decomposition is effected by exposure to air, and one of the chief advantages of ploughing and fallow is to facilitate the decomposition of the disintegrated felspar, which is the chief ingredient of clay soils, and forms part of all soils. Some kinds of felspar are much more slowly decomposed than others, and but a small quantity of potash is available at any one time when such kinds prevail. One crop may entirely exhaust the available potash, and the most liberal supply of phosphates and sulphates will be of little use unless the supply of potash is at the same time attended to. Hence the use of nitre as a manure, or at least one use of it, and of carbonate or sulphate of potash.
But there is another expedient, which acts by increasing the supply of potash. This is the use of lime. The true action of lime is not, as has been supposed, to destroy the organic matter remaining in the soil, but to assist in the decomposition of felspar, which is rapidly decomposed when in contact with quicklime and water. This is the reason why lime is more advantageous in stiff clay soils, which are soils full of felspar.
The burning of very stiff clay also promotes the subsequent action of the weather on the felspar.
In grain crops and in grass much silica is required for the straw. Now silica abounds in all soils, except perhaps some chalky soils. But silica can only enter the plant in the form of alkaline silicates, and therefore the decomposition of felspar which directly supplies silicate of potash is doubly important.
A question naturally arises here. What is the value of organic matter in the soil or in manures. Now it is at once evident that it cannot be essential to the growth of plants as some have stated, that the soil, or the manure, or both, should contain organic matters, or mould, which is organic matter half decayed. For the first plants must have grown in a soil without a trace of mould. Moreover, direct experiment has often proved that plants will thrive in a purely mineral soil, provided it contain all the mineral elements essential to the growth of the plant. In that case the plant obtains from the air exclusively, through water, the carbonic acid and ammonia from which it obtains the whole of its carbon and nitrogen.
But fertile soils do contain mould and other organic matters, as do also most manures. Are these of no use? —far from it. The advantages are these. The slow and constant decay, or oxidation of the mould, &c., gives rise to a constant supply of carbonic acid in the soil itself. A part of this is conveyed to the plant dissolved in water along with the carbonic acid of the air. Another part of it being also dissolved by the water of the soil, dissolves out of the soil carbonates and phosphates of lime, magnesia, and iron, and is the chief means of introducing these into the juice of the plant. And in both ways, in supplying carbon and in supplying mineral matter, this carbonic acid derived from the carbonaceous matter in the soil greatly accelerates the growth of the plants, and very much shortens the period required for them to reach maturity. This, in our northern latitudes, is a matter of the last importance. But even in- Chemnitz dependent of this advantage in point of time, it is probable that a very large part of the phosphates, &c. enters the plant by virtue of the carbonic acid formed in the soil.
The advantages derived from the presence of ammonia in the manure, or of substances yielding it either in the manure or in the soil, is analogous. The plant, if supplied with all the necessary mineral matter, will, indeed, obtain the ammonia, without which it cannot avail itself of these from the atmosphere. But the proportion of ammonia in the air is so small, that a long time in our climate is required for this, and any addition to the supply of ammonia has the effect of enabling the plant to attain maturity sooner.
While, therefore, the plant is not absolutely dependent on the presence of organic matter in the soil or in the manure, there is a decided advantage in its presence there.
Those who have employed a special manure, such as gypsum, or bone-dust, or guano, with good effect, are apt to make sure of the same result on repeating the application. But they are often completely disappointed; for the effect of the first application, say that of gypsum, to a soil deficient in it, has been to produce a heavy crop for which gypsum alone was wanting. But it must be remembered that the heavier the crop the more probable it is that the raising of it has exhausted the soil for the time of some one of the other essential elements, perhaps of the phosphates, in which case a second application of gypsum is dead loss.
Again, it often happens that when a special manure has been found very successful, the same farmer or his neighbour immediately applies it to the first field he has in hand, and perhaps derives no benefit whatever from it. The reason is, that a special manure can only do good where the soil is deficient in the substance supplied by that manure. Gypsum will produce astonishing effects on soils destitute of that substance, but containing all the other elements of fertility; but if added to a soil which, like very many, contains already far more gypsum than is required for many crops, it is merely thrown away.
The advantage of rotation of crops is very obvious. Both the phosphates, which are usually minutely diffused in rocks, and silicate of potash, so essential to grain crops, are only rendered gradually available by the gradual disintegration and decomposition of the felspar and other rocks. If, then, by one crop, one mineral element has been more exhausted than another, let us suppose this to be the case with the available or soluble silicate of potash, a grain crop having been raised, a repetition of the same crop would fail for want of a sufficient supply of this material. But a green crop, requiring hardly any, if any, silicate of potash, would find sufficient phosphates, gypsum, lime, and alkalies, and would allow the action of the weather to go on gradually rendering available a new supply of the silicate. This example will illustrate the principle. In the application of it, as of the other principles we have laid down, experience is the best guide, because there are still very many points, the theory or principle of which is quite obscure, but in regard to which the experienced and intelligent farmer acts with confidence. We cannot attempt to do more here than briefly to indicate the general principles of the application of chemistry to agriculture. The agricultural reader must be referred to works expressly written on this most important subject, such as those of Davy, Liebig, Johnston, and others.
We have now brought to a conclusion the brief and imperfect sketch which we proposed to give of organic chemistry. Our limited space made it absolutely necessary to condense and select the matter presented to the reader. Moreover, the science is in a state of transition, and of very rapid progress, which renders the task doubly difficult. We have endeavoured to lay down, as much as possible, leading principles, and to avoid mere details. We have not even dedicated a section to the destructive distillation of organic substances; but most of the products will be found alluded to under various heads, as those of the hydurets of the ethylie and acetic radicals, the volatile bases of the ethylie and benzoic series, acetic acid, &c., &c.
We can only trust that the difficulty of condensing so large and varied a multitude of facts and their relations into so small a space will excuse the many imperfections of the execution.
(w.g.)