a concrete, gummy, resinous juice brought from the East Indies, usually in large masses, composed of little lumps or tears, of a milky colour, but soon changing, upon being exposed to the air, to a yellowish hue. We now know that the plant which affords this juice is Dorema ammoniacum. It is one of the Umbelliferae (Pent. digyn.), and grows on an arid soil in the province of Irak in Persia, 42 miles from Isfahan. It grows also near Herat in Khorassan, and on the north-western slopes of the Himalayas. The plant is said also to grow in Nubia, Abyssinia, and the interior parts of Egypt. It is brought to the western parts of Europe from Egypt, and to England from the Red Sea, by ships trading to the east. Such tears as are large, dry, free from little stones, seeds, or other impurities, should be picked out, and preferred for internal use; the coarser kind is purified by softening it in hot water and colature, and then carefully inspissating it; unless this be skilfully done, the gum will lose a considerable portion of its more volatile parts. There is often vended in the shops, under the name of strained gum-ammoniacum, a composition of ingredients much inferior in virtue. Ammoniac has a nauseous, sweet taste, followed by a bitter one; and a peculiar smell, somewhat like that of galbanum, but more grateful; it softens in the mouth, and grows of a whiter colour when chewed. Thrown upon live coals, it burns away in flame. It is partially soluble in water and in vinegar, with which it assumes the appearance of milk; but the resinous part, amounting to about one-half, subsides on standing. It is of considerable use in the Materia Medica as an antispasmodic.
Sal, a saline substance, formerly much used in dyeing and some other arts. At present not much of it is employed in this country, most of the sal-ammoniac manufactured in Great Britain being sent to Russia.
Sal-ammoniac is usually in the form of a hard, white cake, opaque, or only slightly translucent. Its taste is cooling, saline, and rather disagreeable; though it has been occasionally employed as a seasoner of food. Its specific gravity is 1·441, according to the mean of the experiments of Wallerius, Watson, and Kirwan. It requires rather more than three times its weight of cold water to dissolve it. The primary form is considered to be the cube; but it crystallises also in octahedrons, and in a figure bounded by 24 trapeziums, formed by replacing the angles of the cube by three triangular faces. These, when they increase very much, cause the faces of the cube to disappear, and thus form a 24-sided figure, known in mineralogy by the name of lenite crystal. A hundred parts of alcohol, of the specific gravity 0·884, dissolve 1½ part of this salt. When exposed to a moist atmosphere, it gradually absorbs water, and deliquesces, though very slowly. When heated, it sublimes unaltered in a white smoke, having a peculiar smell, very characteristic of sal-ammoniac. If a cold body be presented to this smoke, the sal-ammoniac condenses on it, and forms a white crust. When thus sublimed, it has the property of carrying along with it various bodies, which, when heated by themselves, are perfectly fixed.
If quicklime or potash be triturated with sal-ammoniac, a strong smell of ammonia exhales. If sulphuric acid be poured upon it, vapours of muriatic acid are separated in abundance. If equal bulks of muriatic acid gas and ammoniacal gas be brought into contact, they immediately combine and condense into sal-ammoniac. These facts, which are well known, show us that sal-ammoniac is a salt composed of muriatic acid and ammonia. The composition of this salt seems to have been first discovered by Tournefort in 1700. The experiments of Geoffroy junior in 1716 and 1723 were still more decisive, and those of Duhamel, in 1755, left no doubt upon the subject. Various experiments have been made by modern chemists to determine the proportions of the constituents of this salt. Dr Thomson first pointed out a process by synthesis, which has the advantage of being very simple, and at the same time rigidly accurate. He observed, that when muriatic acid gas and ammoniacal gas, both as dry as possible, are brought in contact with each other, they always combine in equal volumes; therefore sal-ammoniac is composed of 100 measures of muriatic acid gas, united with 100 measures of ammoniacal gas. Now, 100 inches of muriatic acid gas weigh 40·011 grains, and 100 cubic inches of ammoniacal gas weigh 18·3837 grains. Hence sal-ammoniac is composed of
\[ \begin{align*} \text{Muriatic acid} & : 40\cdot011 \text{ or } 4\cdot625 \\ \text{Ammonia} & : 18\cdot3837 \text{ or } 2\cdot125 \end{align*} \]
But 4·625 is the weight of an atom of muriatic acid, while 2·125 is the weight of an atom of ammonia. Hence, it is evident that sal-ammoniac is a compound of
\[ \begin{align*} 1 \text{ atom muriatic acid} & : 4\cdot625 \\ 1 \text{ atom ammonia} & : 2\cdot125 \end{align*} \]
and that an integrant particle of it weighs 6·750. But there is another way in which the composition of this salt may be viewed. Muriatic acid is a compound of chlorine and hydrogen. It has been shown, that most of the substances hitherto called muriates are in fact chlorides, or combinations of chlorine with the metallic bases of the alkalies, earths, or metallic oxides respectively. Thus, common salt is a chloride of sodium, or a compound of chlorine and sodium; horn silver is a chloride of silver, or a compound of chlorine and silver. If a hole be dug in a piece of sal-ammoniac; if this hole be slightly moistened by breathing on it; if a globule of mercury be put into it, and this globule be subjected to the action of a tolerably powerful galvanic battery, the mercury speedily acquires the consistence of butter, and swells up so as to amount to nearly four times its original bulk. In short, it is converted into an amalgam. Ammonia itself may be substituted for sal-ammoniac; but the experiment, in that case, is attended with greater difficulty. In this case the ammonia is evidently altered by the galvanic energy, and one of its constituents has combined with the mercury, and converted it into an amalgam. If the amalgam be put under water, it is speedily reduced to the state of pure mercury, while in the mean time ammonia and hydrogen gas are evolved. The same thing happens if the amalgam be put into a glass tube without any water. It would appear from this, that, by the galvanic energy, ammonia has been united to hydrogen, and converted into a substance which is capable of amalgamating with mercury.
Now, no instance can be produced of any substance uniting with mercury, and forming an amalgam which retains the metallic lustre, except a metal. Hence we are entitled to infer, that the mercury in the preceding experiment has united with a metal, and that the compound of ammonia and hydrogen is a metal. This supposed compound of ammonia and hydrogen has received the name of ammonium.
Ammonia itself has been shown to be a compound of
\[ \begin{align*} 1 \text{ atom azote} & : 175 \\ 3 \text{ atoms hydrogen} & : 0.375 \\ & = 2.125 \end{align*} \]
while muriatic acid is a compound of
\[ \begin{align*} 1 \text{ atom chlorine} & : 4.5 \\ 1 \text{ atom hydrogen} & : 0.125 \\ & = 4.625 \end{align*} \]
Were the atom of hydrogen in the muriatic acid to combine with the ammonia and convert it into ammonium, then ammonium would be a compound of
\[ \begin{align*} 1 \text{ atom azote} & : 1.75 \\ 4 \text{ atoms hydrogen} & : 0.50 \\ & = 2.25 \end{align*} \]
The integrant particle of it would weigh 2.25. We might conceive sal-ammoniac to be a compound of
\[ \begin{align*} 1 \text{ atom chlorine} & : 4.5 \\ 1 \text{ atom ammonium} & : 2.25 \\ & = 6.75 \end{align*} \]
According to this view, it would be a chloride of ammonium. The atomic constituents are the same according to both views; the only difference lies in the way in which these atoms are united. If sal-ammoniac be a muriate of ammonia, then one atom of hydrogen is united with one atom of chlorine, constituting muriatic acid, while three atoms of hydrogen are united with one atom of azote, constituting ammonia. If it be a chloride of ammonium, then four atoms of hydrogen are united to one atom of azote, constituting ammonium, an integrant particle of which is united to an atom of chlorine. It is impossible to determine, in the present state of chemical knowledge, which of these views is the true one. We have no other evidence of the existence of ammonium than the amalgam formed with mercury by means of sal-ammoniac and the galvanic battery, and the resolution of this amalgam into mercury, ammonia, and hydrogen. But this curious experiment is not easily explained upon any other supposition.
The name ammoniacus sal occurs in Pliny, lib. xxxi. cap. vii. He tells us that it was applied to a kind of fossil salt found below the sand, in a district of Cyrenaica, from which circumstance its name was derived. It was similar in appearance to the alumenum scissile, had a disagreeable taste, but was useful in medicine. The general opinion is, that the sal-ammoniac of the ancients was the same as that of the moderns; but the imperfect description of Pliny is far from being sufficient to decide the point. The native sal-ammoniac of Bucharia, as described by Model and Karsten, and which was analyzed by Klaproth, has no resemblance to the salt described by Pliny. The same remark applies to the sal-ammoniac of volcanoes. Dioscorides, in mentioning sal-ammoniac (book v. chap. cxxvi.), makes use of a phrase quite irreconcilable with the description of Pliny, and rather applicable to rock-salt than to our sal-ammoniac. Sal-ammoniac, he says, is peculiarly prized if it can be easily split into rectangular fragments. Finally, we have no proof whatever that sal-ammoniac occurs at present, either near the temple of Jupiter Ammon, or in any part of Cyrenaica. These circumstances induce us to conclude that the term sal-ammoniac was applied as indefinitely by the ancients as most of their other chemical words. It may have been given to the same salt which is known to the moderns by that appellation, but was not confined to it.
The name sal-ammoniac is derived, according to some, from the temple of Jupiter Ammon, in the neighbourhood of which it was found; according to others, from a district of Cyrenaica called Ammonia; but according to Pliny, from the sand in which it occurred,—the Greek name for sand being aqua.
But whether our sal-ammoniac was known to the ancients or not, there can be no doubt that it was well known to the alchemists. Albertus Magnus, in his treatise De Alchymia, informs us, that there were two kinds of sal-ammoniac, a natural and an artificial. The natural was sometimes white, and sometimes red; the artificial was more useful to the chemist. He does not tell us how it was prepared, but he describes the method of subliming it, which can leave no doubt that it was real sal-ammoniac. In the Opera Minraria of Isaac Hollandus the father, addressed to his son, there is likewise a description of the mode of subliming sal-ammoniac. There can be no doubt, then, that true sal-ammoniac was known in the thirteenth century. Basil Valentine, in his Curios Triumphalis Antimonii, describes some of the peculiar properties of sal-ammoniac in a still less equivocal manner, if possible; but, after the two older writers already quoted, his evidence is unnecessary.
Sal-ammoniac occurs native in Bucharia, and probably in other parts of the world. It is found also in small quantities near volcanoes, being formed during the extraordinary convulsions of these mountains. This fact seems in corroboration of an opinion advanced by some mineralogists, that the principal fuel of volcanoes is pit-coal, and that they are always moistened with sea-water; for sal-ammoniac is sublimed in small quantities during the burning of London bricks, the sand of which is brought from the sea-shore, while the fuel is pit-coal. In the Latin, English, and French chemical books published in the seventeenth and the beginning of the eighteenth century, the name of this salt is usually written sal-ammoniac. This we conceive to be an old German word; for Agricola has given us an alphabetical catalogue of all the Latin technical terms which he uses in his works, with a German translation of each. Now, the German translation which he gives of sal-ammoniacus is sal-armoniac. The present German name for this salt is salmiak.
Egypt is the country where sal-ammoniac was first manufactured, and from which Europe for many years was supplied with it. This commerce was first carried on by the Venetians, and afterwards by the Dutch. Nothing was known about the method employed by the Egyptians till the year 1719. In 1716 Geoffroy junior read a paper to the French academy, showing that sal-ammoniac must be formed by sublimation; but his opinion was opposed so violently by Homberg and Lemery, that the paper was not printed. In 1719 M. Lemaire, the French consul at Cairo, sent the academy an account of the mode of manufacturing sal-ammoniac in Egypt. The salt, it appeared, was obtained by simple sublimation from soot. In the year 1760 Linnaeus communicated to the Royal Society a correct detail of the whole process, which he had received from Dr Hasselquist, who had travelled in that country as a naturalist. This account is published in the 51st volume of the Philosophical Transactions, 1760, p. 504. Almost the only fuel used in Egypt is the dung of cattle. This is collected during the first four months of the year, when the cattle feed on spring grass, which in Egypt is a kind of clover. It is dried, and sold to the common people as fuel. The soot from this fuel is carefully collected and sold to the sal-ammoniac makers, who only work during the months of March and April; for at other periods of the year the dung of their cattle is not fit for their purpose. An oblong oven is built of bricks and moist dung, as long again as broad, and of such a size that the outside or flat part of the top of the arch may hold fifty glass vessels, ten in length, and five in breadth, each vessel having a cavity left for it in the brick work of the arch. These glass vessels are globular, with a neck an inch long and two inches wide. In general they are about eighteen inches in diameter. Each vessel is coated over with a fine clay found in the Nile, and afterwards with straw. They are filled two thirds with soot, and put into their holes at the top of the oven. At first a gentle fire is raised, and the temperature is gradually increased to the highest degree, at which it is kept for three days. A smoke with a sourish smell, not unpleasant, issues first from the glasses, then the salt sublimes, and coats the upper part of the vessel.
It was long supposed that camels' urine and camels' dung were essential for the success of the above process; but this is a mistake. The dung of black-cattle, horses, sheep, goats, &c. are all used promiscuously. The dung of these animals contains the sal-ammoniac ready formed. This depends upon the food which the animals live on, and accordingly it is only fit for the purpose at one season of the year. The soot contains the sal-ammoniac likewise ready formed, and merely mixed with a quantity of charcoal, oil, &c. from which it is freed by sublimation. Chaptal informs us that he found sal-ammoniac in the soot obtained by burning the dung of cattle that had fed on the saline plants in the marshes near the Mediterranean. Thus the Egyptian method of obtaining sal-ammoniac is the simplest possible.
The first attempt to manufacture sal-ammoniac in Europe was made by Mr Goodwin, a chemist of London, about the beginning of the eighteenth century. We do not know his process accurately; but he appears to have used the mother ley of common salt and putrid urine as ingredients. Dossie, in his Institutes of Experimental Chemistry, gives it as his opinion, that the salt obtained by this process was not sal-ammoniac, but sulphate of ammonia, and even describes a process for subliming that salt. But he must have been mistaken; for sulphate of ammonia, as appears from the experiments of Hatchett, is entirely decomposed when we attempt to sublime it. Goodwin's process, however, whatever it was, did not succeed, and was speedily abandoned. In the year 1740 a patent was taken out for making sal-ammoniac by a London manufacturer. The process was nearly the same as Goodwin's, and was equally unsuccessful. The first successful manufacture of sal-ammoniac in this country was established in Edinburgh by Dr Hutton and Mr Davy. We do not know in what year the manufactory was begun; but as the plan was concerted while these gentlemen were students at the university of Edinburgh, the establishment of the work cannot have been far from the year 1760. From the university of Edinburgh, Dr Hutton went to Paris. During his absence Mr Davy began the manufactory, and on his return admitted him as a partner. This original manufactory existed in Edinburgh till within these few years. The low price of sal-ammoniac during the war with Russia induced the proprietors to abandon it, as was the case with almost all the sal-ammoniac works in Britain.
Sal-ammoniac was first manufactured in France by Baumé, who established a work about the year 1760; but whether it was posterior or anterior to the work of Hutton and Davy, we do not know. Manufactories of it were afterwards established in Germany, Holland, and Flanders.
Various modes were followed in Europe to procure this salt. But the theory (if we can apply the term here) of most of the manufacturers was the same. They formed a sulphate of ammonium, which they mixed with common salt. A double decomposition took place. The sulphuric acid of the sulphate united with the soda of the common salt, and formed Glauber's salt, which was obtained in great abundance by crystallization, and sold as a medicine. The muriatic acid and ammonia, uniting together, formed sal-ammoniac, which was sublimed. When the British government imposed a heavy duty on Glauber salts, the manufacture of sal-ammoniac in this country received so severe a blow, that it is not likely ever to recover it. We shall give a short sketch of the processes followed in different manufactories, in order to afford a more distinct idea of the method of procuring this salt.
Before the French revolution, several manufactures of sal-ammoniac existed in Flanders, which deserve to be described; first, because they were in some measure an imitation of the original Egyptian method. Bricks, or rather balls, were formed of the following materials: twenty-five parts of pounded pit-coal, five parts of soot, two parts of clay, and as much of a saturated aqueous solution of common salt as was sufficient to convert the whole into a paste; this paste was moulded in an iron mould, and the balls suffered to dry. These were burnt in a brick furnace, along with a quantity of dry bones, the proportion of which does not appear to have been accurately determined. The furnace communicated by an aperture, two inches wide, into a vaulted brick chamber above. From the top of this chamber there was a communication, likewise two inches wide, with a horizontal gallery, which terminated in a perpendicular chimney. The fire was kept up with these materials for five or six Ammoniac, months, and then allowed to go out. By the combustion of the pit-coals, soot, and bones, a quantity of carbonate of ammonia is formed. The common salt is decomposed by the clay, and muriatic acid disengaged. This acid coming in contact with the carbonate of ammonia, decomposes it, and sal-ammoniac is formed. The sides and roof of the vaulted chamber are found coated with this impure sal-ammoniac, which is carefully removed. The bottom of the chamber, and the horizontal gallery above, contain likewise sal-ammoniac, but so much loaded with bitumen, that it requires to be burnt a second time before the sal-ammoniac can be extracted. The impure sal-ammoniac is put into egg-shaped clay vessels, twenty inches long and sixteen in diameter. Each is filled to within three inches of the top. The lower part of these vessels is exposed to a graduated heat for forty-eight hours, while the upper part, being left in the air, is comparatively cool. The oily matter is first driven off, and then the sal-ammoniac is sublimed in a cake in the upper part of the vessel. The charcoal, and any other fixed matter present, remains at the bottom. Finally, the clay vessels are broken, and the cakes of sal-ammoniac taken out. There is a small hole in the upper part of the clay vessels, and care is taken to keep this hole open during the whole process, to prevent the vessels from bursting. Fifteen parts of the sooty matter taken from the vaulted chambers yield about five parts of sal-ammoniac. (Journal des Mines, No. X. p. 3.)
The original process of Baumé was to distil animal substances, in order to procure from them carbonate of ammonia. With this salt he decomposed the muriate of magnesia, which exists in considerable quantity in the mother ley of common salt, when that substance is procured from sea-water; the liquid containing the sal-ammoniac was evaporated, and the sal-ammoniac sublimed. This process was speedily abandoned, and another substituted in its place by MM. Leblanc and Dizé. They brought into contact, in a leaden chamber, vapours of ammonia and of muriatic acid. The ammonia was procured by distilling animal substances, and the muriatic acid by decomposing common salt by means of sulphuric acid. But this method, though it yielded a very pure sal-ammoniac, was speedily abandoned on account of its expense.
The process of Hutton and Davy was to procure ammonia, which they did chiefly from soot. This they converted into sulphate of ammonia. The sulphate was mixed with common salt, and thus two salts were procured; Glauber's salt, which they obtained by crystallization, and sal-ammoniac, which was sublimed.
Almost all the manufactures of sal-ammoniac, whether in Britain, France, or Germany, were similar in principle to that of Hutton and Davy. The only difference consisted in the means employed to procure the sulphate of ammonia. We shall describe a manufacture, formerly existing in London, in which the methods employed were both scientific and economical.
The material from which the ammonia was extracted was bones. These were collected in the streets and from dunghills, chiefly by old women. The bones were bruised and boiled, in order to extract the fat which they contained, which was sold to the soap-makers. They were then put into iron cylinders eight feet long and three feet in diameter, placed horizontally over a fireplace, so that they could be made red-hot. At one end of the cylinder was a mouth, about fourteen inches in diameter, by which the bones were introduced. This mouth was accurately shut by a cover, and made air-tight by means of lute. From the other end of the cylinder proceeded a cast-iron pipe, from six to eight inches in diameter, and twenty feet long, terminating in one or more oblong leaden receivers, which were kept cool by water placed in a leaden vessel, the bottom of which formed their cover, the juncture being secured by lute. Of these receivers there were commonly two to each still, or three to two stills. Every receiver was about twelve feet long, one foot deep, and fourteen inches wide; and the refrigeratory that covered it held about four inches in depth of water. At the end most remote from the still was a pipe, fitted with a wooden plug, for the purpose of drawing off the condensed liquor; and above this was a hole through which the gas and uncondensable vapour passed off into the open air.
A single charge of each still yielded about 36 pounds of impure alkaline liquor, and about 30 pounds of black fetid oil floating on its surface. This latter being skimmed off, the ammonia was saturated with sulphuric acid, either by means of the mother liquor from the green vitriol makers, or still more economically by means of calcined and pulverized gypsum. In this last case the materials were mixed, and left in contact for some hours. A double decomposition took place; the sulphuric acid of the gypsum uniting with the ammonia, while the carbonic acid of the carbonate combined with the lime of the gypsum. The solution of sulphate of ammonia thus produced was mixed with common salt, by which Glauber's salt and sal-ammoniac were formed, and separated from each other.
For this purpose the liquid, clarified by subsidence and decantation, was transferred into oblong leaden boilers, about nine feet long, three wide, and nine inches deep. Two thirds of the length of these boilers were set upon iron plates heated by a fire beneath; the remaining part was supported by flat tiles, and defended from the heat by a solid brick work. As the water evaporates, the Glauber's salt begins to crystallize. It is swept from time to time to the cool extremity of the boiler, whence it is shovelled into baskets placed over the end of the boiler, that the liquid which drains off may not be lost. The evaporation is continued till feathered crystals of sal-ammoniac begin to appear on the surface. The liquid is then run into coolers, and deposits little else than sal-ammoniac till the temperature sinks to 70°. The crystals must now be removed, that they may not be mixed with the Glauber's salt, which begins at that temperature to be deposited. The sal-ammoniac thus obtained is first drained in baskets, and then exposed to heat in a kind of oven, till the water of crystallization is driven off. It becomes spongy, friable, of an ash-colour, mixed with small white filaments.
This salt is introduced, while still hot, into globular grey earthen jars, fitted with a cover (with a hole of about half an inch diameter in its centre), luted on with a mixture of clay and horse-dung. These are set in earthen pots over a strong fire, in a furnace of either a circular or oval form, and capable of containing from six to eighteen, surrounded with sand up to the edge of the pot, and also having about 2½ inches of sand on the cover, confined by an iron ring about three inches deep, and two inches less in diameter than the cover, in order that the luting, should it give way, may be repaired without suffering the covers to be cooled by the removal of the sand; for, during the sublimation, their temperature should be about 320°. These earthen vessels may be filled with the dried salt to within two inches of the top. It may be gently pressed in, but not rammed close. The fire, which has been lighted some time before, is now to be raised gradually till the iron pots are of a pretty strong red heat all