a parliamentary borough in a valley watered by the Chelt, and sheltered by the Cotswold Hills, Gloucestershire, 88 miles N.W. from London. Although an ancient town and existing under the Romans it was a place of no importance till the discovery of its saline springs, containing muriate of soda, sulphate of soda, and sulphate of magnesia, in the beginning of the eighteenth century. From its comparatively modern origin, the streets and buildings of Cheltenham are spacious and elegant, and its promenades are reckoned among the finest in England. St Mary's church is a cruciform edifice with a lofty octagonal spire, and contains a curious font and ancient stone cross. Trinity church and Christ church are modern, and are much admired. Besides these there are several other established and numerous Dissenting churches. It contains a proprietary college (capable of containing 300), a Church of England training college, and numerous schools and charities. Cheltenham contains no manufacturing establishments of any importance. It is the seat of a county court, and returns one member to the imperial parliament. Pop. (1851) 35,051.

CHEMISE, in Fortification, the wall with which a bastion or any other bulwark of earth is lined, for its greater support and strength. CHEMISTRY.

Chemistry, as a regular branch of natural science, is of comparatively recent origin, and can hardly be said to date from an earlier period than the latter third of the past century. It is true that, before that time, many men of high talent and wonderful ingenuity had devoted themselves to chemical studies; and the very name of the science, which, with the prefixed article, forms the well-known word Alchemy, is of Arabian origin. The early Greek philosophers had some vague yet profound ideas on the subject, but their acquaintance with it was limited chiefly to speculation a priori, founded on a general and often inaccurate observation of natural phenomena. Yet their acuteness was such, that some of their speculations as to the constitution of matter coincide in a most wonderful manner, as will be hereafter shown, with those which are now beginning to prevail among the most profound modern philosophers.

In these early ages, and long afterwards, those who turned their attention to the experimental part of the subject, which the Greeks hardly attempted, did so with some other object in view than the mere cultivation of chemistry as a science for its own sake. They either laboured to discover and produce new remedies, and in this manner were led to the search after the panacea or universal remedy, the elixir vitae, and similar desiderata, which indeed formed the chief occupation of alchemists, as chemists were then called, for many centuries; and these transcendental researches, while they failed in their professed objects, yet led to the discovery of many of the best known and most important compounds of chemistry, as well as of many most valuable medicines. Or else, on the other hand, led by speculations as to the nature of the material elements, which are much less absurd, or at least were then much less absurd, than we are apt to suppose, they attempted to effect the transmutation of one element into another, and especially of the baser metals into gold and silver. In this way arose the search after the philosopher's stone, supposed to be capable of effecting this transmutation, and after the universal menstruum or solvent, which was expected to have similar effects, or at least to facilitate the necessary processes. In this pursuit, as in the other, the alchemists failed; but their indefatigable industry and their wonderful ingenuity led them to numerous discoveries neglected at the time in many instances, but which have had a most marked and important influence on the development of the modern science.

It has already been said, that the alchemists did not study chemistry as a science, but only practised it as a means of attaining their objects. They proceeded on certain speculative notions, adopted a priori, and supposed to be established truths. But at last the time came, when the materials they had collected with so much industry and zeal were made the foundation, on the Baconian or inductive system, of a new science. This could not take place until after the development of physics, or mechanical philosophy, which treats of those properties which are common to all material substances, and which development immediately followed or accompanied that of astronomy.

From the very nature of chemistry, it was impossible that it should take a truly scientific form, until the balance was applied to it. Up to that time, speculations a priori, and erroneous interpretations of observed phenomena, retarded its progress, although new and important discoveries were daily made. But Lavoisier, who first employed the balance in the study of some of the most important phenomena, such as those of combustion, on a certain theory of which the then existing science was founded, effected a complete revolution in chemistry; and from that time, 1760-1770, the science of chemistry has made rapid and continuous progress.

Our limited space will not permit us to enter more minutely into the history of chemistry, and we shall therefore at once proceed to give some account of the science as it now stands.

It is not easy, and fortunately it is not necessary, to define chemistry in a few words. We may describe it as the science which treats of the properties of the different kinds of matter, or elementary bodies, which exist in our universe, the laws which regulate their mutual actions, and the proportions in which they combine together to form the compounds which, for the most part, constitute the animal, vegetable, and mineral kingdoms, as well as the properties of these compounds. But it is necessary here to explain the term elementary body or element.

ELEMENTARY BODIES.

The ancients, as is well known, admitted four elements, earth, water, air, and fire, of which all things were composed. But it is a mistake to suppose that they used the term element in the same sense as we do. That which they understood by it was rather the forms under which matter is presented to us, than the nature or essence of material substances. Thus, by earth they understood solid matter; by water, liquid matter; and by air, matter in the state of gas or vapour. Fire was their name for what we call heat or caloric, which causes solid bodies to become liquid, liquids to become gaseous. And in this sense the four elements of the ancients do indeed include all material substances.

The meaning now attached to the word element is very different from this. We observe that there are different kinds of matter, whether solid, liquid, or gaseous; and on investigation we find that some of these may be resolved into two or more different substances, some of which again may in like manner be resolved into others, but at last we come to substances in which we are unable, with all our appliances, to detect more than one kind of substance or matter. Some such substances occur in nature, although most natural substances contain more than one kind of matter. To take a few examples. Common salt can easily be shown to consist of two different kinds of matter; of a metal, sodium, and of a non-metallic body, chlorine. Water can be resolved into two gaseous non-metallic substances, oxygen and hydrogen. Cinnabar consists of mercury and sulphur; marble of three bodies, the metal calcium, the non-metallic body carbon, and oxygen. But it is out of our power, by any means yet known to us, to detect any other substance in sodium, chlorine, oxygen, hydrogen, mercury, sulphur, calcium, and carbon; sodium yields only sodium, sulphur only sulphur, and so on. And when this is the case—when a body cannot be proved to contain more than one kind of matter—it is called an element or elementary body, because such bodies are, in fact, the elements of which the material world around us is made up. Some elementary bodies are found in nature as such—for example, mercury, sulphur, carbon, gold, silver, iron, copper, and a few others; but in general two or more are found united, as in air, water, rocks, earths, plants, and animals.

It must be observed, that when we call a substance, such as carbon or chlorine, elementary or simple, we do not assert that it is absolutely and certainly simple, or may not be found hereafter to contain more than one kind of matter; we only mean that, to us, or so far as our knowledge extends, it is so. Thus, at the beginning of the present century potash and soda were considered elementary, be- Chemistry—cause no one could prove them to be compounded; yet soon afterwards, by the aid of a new power, that of galvanism, Davy succeeded in showing that they contained each a metal, potassium and sodium, united to oxygen. It may happen that some future chemist should find the means of proving that these metals themselves contain more than one kind of matter, in which case they would no longer be called elementary. Nay, it is even considered probable, that all the metals may ultimately prove to be compounds, not elements; and the same opinion is entertained regarding such elements as chlorine, bromine, and iodine. But so long as this is not demonstrated, these bodies, and all others in the same position, must be retained on the list of elements.

The researches of chemists have, up to this time, detected about 60 elementary substances; of which 12 are non-metallic, and the rest all metals. The non-metallic bodies are also called metalloids.

Of these elements, the whole of our earth, including the waters and the atmosphere belonging to it, and likewise all the living organisms, whether animal or vegetable, are made up. But it is only a small number of the elements which occur in any great abundance; for the majority, especially of the metals, are only found in a few rare and scattered minerals.

The following table exhibits the elements arranged alphabetically. The second column contains the symbols or abbreviations used to represent them in chemical notation, and the third contains the numbers which represent their respective combining proportions, as ascertained by experiment, that of hydrogen being made the standard of comparison = 1. The meaning and value of these numbers will be presently explained.

| Elements | Symbols | Hydrogen = 1 | |---------------------------|---------|--------------| | Aluminum | Al | 137 | | Antimony (Stibium) | Sb | 129 | | Arsenic | As | 75 | | Barium | Ba | 89-6 | | Bismuth | Bi | 71 | | Boron | B | 10-9 | | Bromine | Br | 80 | | Cadmium | Cd | 56 | | Calcium | Ca | 20 | | Carbon | C | 6 | | Cerium | Ce | 47 | | Chlorine | Cl | 35-5 | | Chromium | Cr | 26-7 | | Cobalt | Co | 29-5 | | Columbium (Tantalum) | Ta | 92 | | Copper (Caprum) | Cu | 31-7 | | Didymium | D | 49-61 | | Erbium | E | 1 | | Fluorine | F | 18-9 | | Glucinium | G | 26-5 | | Gold (Aurum) | Au | 99-6 | | Hydrogen | H | 1 | | Iodine | I | 127-1 | | Iridium | Ir | 99 | | Iron (Ferrum) | Fe | 28 | | Lanthanum | La | 47-1 | | Lead (Plumbum) | Pb | 103-7 | | Lithium | Li | 6-5 | | Magnesium | Mg | 12-2 | | Manganese | Mn | 27-6 | | Mercury (Hydrargyrum) | Hg | 200 | | Molybdenium | Mo | 46 | | Nickel | Ni | 29-6 | | Niobium | Nb | 7 | | Nitrogen | N | 14 | | Osmium | Os | 99-6 | | Oxygen | O | 8 | | Palladium | Pd | 53-3 | | Pelopium | Pe | 1 | | Phosphorus | P | 32 | | Platinum | Pt | 98-7 | | Potassium (Kallum) | K | 39-2 | | Rhodium | R | 52-2 | | Ruthenium | Ru | 52-2 | | Selenium | Se | 39-5 |

Those elements, the names of which are printed in small capitals, are the most abundant and the most important; for of them, practically, the mass of the globe and all its inhabitants, the sea and the air, are composed.

Thus, the air consists for the most part of only two elements, oxygen and nitrogen; water of two, oxygen and hydrogen; sea salt of two, sodium and chlorine; calcareous matter, such as marble, limestone, chalk, and Iceland spar, as well as the earthy part of shells, of three elements, carbon, calcium, and oxygen. Silica, quartz, or sandstone, contains silicon and oxygen; gypsum consists of sulphur, calcium, and oxygen; bone earth of phosphorus, calcium, and oxygen; woody fibre of carbon, hydrogen, and oxygen; muscular fibre of carbon, hydrogen, nitrogen, sulphur, and oxygen; pure clay of aluminium and oxygen; iron ore of iron and oxygen, or of carbon, iron, and oxygen; lead ore of lead and sulphur; copper ore of copper and sulphur.

The ashes of land plants contain much carbonate of potash, that is carbon, potassium, and oxygen; those of sea plants, carbonate of soda, or carbon, sodium, and oxygen. Many, indeed most, rocks and soils are more complex, being mixtures of several of the substances just enumerated. Thus, granite, gneiss, and mica slate, all contain quartz, felspar, and mica; and the two latter minerals are compounds of silica with clay or alumina, potash, lime, &c. Clay slate, gneisswacke, and other rocks, consist chiefly of felspar; and the beds of coal contain much carbon, with less hydrogen, nitrogen, and oxygen, than the vegetables from which they are derived. Soils are rocks, more or less disintegrated; but contain the same substances, namely, quartz or silica, clay or alumina, limestone, felspar, gypsum, &c., which are found in the rocks which yield them, generally mixed with decaying vegetable matter or mould.

The preceding statements will show how small is the number of the more important elements; that is, of those which constitute an important part of the earth's crust. And even among the substances named there are one or two, such as the ores of lead and copper, which occur only in veins and in comparatively small quantity. But these metals, and a good many others, such as gold, silver, mercury, zinc, antimony, chromium, arsenic, cobalt, nickel, platinum, magnesium, &c., although, in comparison with the more abundant elements their quantity is small, yet occur in sufficient abundance to be applied to innumerable useful purposes.

Iron, although its ores are scarce, compared with the common rocks, is yet, in small proportion, so universally diffused that it may be reckoned among those elements which make up the chief part of the earth's crust.

It will be seen that of all the elements oxygen is the most universally present, forming a constituent part, indeed, of all rocks and soils, excepting only rock salt, which is hardly to be called a true rock; or of all plants and animals, of water, and of the air. It cannot, therefore, be doubted that oxygen is of all the elements the most important.

Next to it, in the mineral kingdom, come silicon, aluminium, calcium, carbon (in limestone), sodium, chlorine, Chemistry (these two in salt), hydrogen (in water), nitrogen (in air), magnesium, iron, potassium, and sulphur, and in smaller proportion, phosphorus, iodine, bromine, and fluorine, besides the ores of metals.

But in the animal and vegetable kingdoms, while nearly the same elements form their mass, the proportions vary much. Carbon is the predominant and characteristic element of all organized structures; after it come hydrogen, nitrogen, oxygen, phosphorus, and calcium (in bones), sulphur, potassium, chlorine, sodium, and in smaller proportion iodine and fluorine. Aluminium hardly occurs in the organized world.

It is thus obvious, that there is no essential distinction, so far as concerns the mere nature of the elements, between the mineral and the organized kingdoms of nature. The principal elements of both are the same; and the difference lies, first, in the predominance of oxygen in the former, and of carbon in the latter; and, secondly, in the more complex nature, as we shall hereafter see, of the chief compounds which enter into the formation of organized tissues.

It is hardly necessary to point out, that by the very definition we have given of the term element, it is implied that we cannot transmute one element into another. We do not mean to assert that it is absolutely or physically impossible to transmute one of our so-called elements into another, but only that we cannot do this up to the present time. And there is every reason to believe that if we should ever succeed in transmuting one of our elements into another, it would be in consequence of our discovering, which is quite conceivable, that one or both of the transmutable bodies was in reality a compound, and not a true element. There are certain groups which have so many characters in common to all the members of them, that the simplest explanation would seem to be, that all these members contain one common ingredient or element, to which the common properties are to be ascribed, and which, in each case, is combined with a different element, to which the differences are due.

Thus all the metals agree in having the metallic lustre, and in conducting heat and electricity, besides having a general resemblance in their chemical characters; and it is conjectured that all metals contain one common ingredient. But if this be so, the metals cease to be simple elementary bodies, and must be compound. Again, there is a wonderful and accurately graduated analogy between chlorine, bromine, and iodine, in all their characters; and the opinion is pretty generally held, that they also will ultimately prove to be compound bodies, and to possess a common ingredient. But this, in the meantime, is but conjecture.

When we shall have explained the views now held as to the atomic constitution of matter, we shall mention another conjecture as to the possibility of the transmutation of bodies truly elementary. For the present it may suffice to point out that if such transmutation be supposed possible, it must be under circumstances very different from those which commonly exist. For if it were possible, under existing circumstances, that one element should become converted into another, the whole foundation, not only of chemistry, but of nature, would be destroyed. If, for example, carbon, the predominating and essential element of organized beings, could, under ordinary circumstances, be converted, as has been alleged, into silicon, one of the chief elements of mineral nature, how could plants or animals, to which carbon, as such, is essential, possess any stability? As soon as the carbon of any vegetable or animal tissue became silicon, that tissue must cease to exist. Again, if such transformation were possible, under the usual conditions of experiment, chemical analysis would be utterly impracticable, since it would be impossible to determine with accuracy the amount or weight of an element, liable at any time to become a different one. It is easy to see that an indispensible condition of the very existence of the material world we inhabit is the stability of the elements of which it is made up. An unstable element is almost a contradiction in terms; and, therefore, practically, the transmutation of elements, under the usual conditions of experiment, must be regarded as necessarily unattainable, although it may be conceivable under widely different circumstances. And when we speak of the indispensable stability of elementary bodies, it is altogether independently of the question whether these be really elementary, or, as is perhaps more probable in many cases, compounds which we are unable to decompose, or prove to be compounds. Thus, whether carbon be really elementary or not, it must be a stable element to us, otherwise the compounds it forms could have no stability.

Having explained what is understood by elements or elementary bodies, we shall next proceed, before describing the elements individually, to mention briefly the important laws which regulate chemical action between different elements, and especially those which have reference to the proportions, by weight as well as by volume, in which they combine together. It will also be necessary to explain the atomic hypothesis, which is adopted to furnish an explanation of the facts alluded to.