INTRODUCTION.

In this Introduction I shall first present a GENERAL VIEW of the objects of chemistry, along with a scheme for converting the alphabetical arrangement adopted in this volume, into a systematic order of study. I shall then describe the manner in which this Dictionary seems to have been originally compiled, and the circumstances under which its present regeneration has been attempted. This exposition will naturally lead to an account of the principles on which the investigations of chemical theory and facts have been conducted, which distinguish this Work from a mere compilation. Some notice is then given of a treatise on practical chemistry, publicly announced by me upwards of three years ago, and of the peculiar circumstances of my situation as a teacher, which prompted me to undertake it, though its execution has been delayed by various obstructions.

THE forms of matter are numberless, and subject to incessant change. Amid all this variety which perplexes the common mind, the eye of science discerns a few unchangeable primary bodies, by whose reciprocal actions and combinations, this marvellous diversity and rotation of existence, are produced and maintained. These bodies, having resisted every attempt to resolve them into simpler forms of matter, are called undecompounded, and must be regarded in the present state of our knowledge as experimental elements. It is possible that the elements of nature are very dissimilar; it is probable that they are altogether unknown; and that they are so recondite, as for ever to elude the sagacity of human research.

The primary substances which can be subjected to measurement and weight, are fifty-three in number. To these, some chemists add the imponderable elements,-light, heat, electricity, and magnetism. But their separate identity is not clearly ascertained.

Of the fifty-three ponderable principles, certainly three, possibly four, require a distinct collocation from the marked peculiarity of their powers and properties. These are named Chlorine, Oxygen, Iodine (and Fluorine?) These bodies display a pre-eminent activity of combination, an intense affinity for most of the other forty-nine bodies, which they corrode, penetrate, and dissolve; or, by uniting with them, so impair their cohesive force, that they become friable, brittle, or soluble in water, however dense, refractory, and insoluble they previously were. Such changes, for example, are effected on platinum, gold, silver, and iron, by the agency of chlorine, oxygen, or iodine. But the characteristic feature of these archeal elements is this, that when a compound consisting of one of them, and one of the other forty-nine more passive elements, is exposed to voltaic electrization, the former is uniformly evolved at the positive or vitreoelectric pole, while the latter appears at the negative or resino-electric pole.

The singular strength of their attractions for the other simple forms of matter, is also manifested by the production of heat and light, or the phenomenon of combustion, at the instant of their mutual combination. But this phenomenon is not characteristic; for it is neither peculiar nor necessary to their action, and, therefore, cannot be made the basis of a logical arrangement. Combustion is vividly displayed in cases where none of these primary dissolvents is concerned. Thus some metals combine with others with such vehemence as to elicit light and heat; and many of them, by their union with sulphur, even in vacuo, exhibit intense combustion. Potassium burns distinctly in cyanogen (carburetted azote), and splendidly in sulphuretted hydrogen. For other examples to the same purpose, see COMBUSTIBLE and COMBUSTION.

And again, the phenomenon of flame doesnot necessarily accompany any of the actions of oxygen, chlorine, and iodine. Its production may be regulated at the pleasure of the chemist, and occurs merely when the mutual combination is rapidly effected. Thus chlorine or oxygen will unite with hydrogen, either silently and darkly, or with fiery explosion, as the operator shall direct.

Since, therefore, the quality of exciting or sustaining combustion is not peculiar to these vitreo-electric elements; since it is not indispensable to their action on other substances, but adventitious and occasional, we perceive the inaccuracy of that classification which sets these three or four bodies apart under the denomination of supporters of combustion; as if, forsooth, combustion could not be supported without them, and as if the support of combustion was their indefeisible attribute, the essential concomitant of their action. On the contrary, every change which they can produce, by their union with other elementary matter, may be effected without the phenomenon of combustion. See section 5th of article COMBUSTION.

The other forty-nine elementary bodies have, with the exception of azote (the solitary incombustible), been grouped under the generic name of combustibles. But in reality combustion is independent of the agency of all these bodies, and therefore combustion may be produced without any combustible. Can this absurdity form a basis of chemical classification? The decomposition of euchlorine, as well as of the chloride and iodide of azote, is accompanied with a tremendous energy of heat and light; yet no combustible is present. The same examples are fatal to the theoretical part of Black's celebrated doctrine of latent heat. His facts are, however, invaluable, and not to be controverted, though the hypothetical thread used to connect them be finally severed.

To the term combustible is naturally attached the idea of the body se named affording the heat and light. Of this position, it has been often remarked, that we have no evidence whatever. We know, on the other hand, that oxygen, the incombustible, could yield, from its latent stores, in Black's language, both the light and heat displayed in combustion; for mere mechanical condensation of that gas, in a syringe, causes their disengagement. A similar condensation of the combustible hydrogen, occasions, I believe, the evolution of no light. From all these facts, it is plain, that the above distinction is unphilosophical, and must be abandoned. In truth, every insulated or simple body has such an appetency to combine, or is solicited with such attractive energy by other forms of matter, whether the actuating forces be electo-attractive, or electrical, that the motion of the particles constituting the change, if sufficiently rapid, may always produce the phenomenon of combustion.

Of the forty-nine resino-polar elements, forty-three are metallic, and six non-metallic.

The latter group may be arranged into three pairs:

Ist. The gaseous bodies, Hydrogen and AzOTE;

2d. The fixed and infusible solids, CARBON and BORON;

3d. The fusible and volatile solids, SULPHUR and PHOSPHORUS. The forty-three metallic bodies are distinguishable by their habitudes with oxygen, into two great divisions, the BASIFIABLE and ACIDIFIABLE metals. The former are thirty-six in number, the latter seven.

Of the thirty-six metals, which yield by their union with oxygen salifiable bases, three are convertible into alkalies, ten into earths, and twentythree into ordinary metallic oxides. Some of the latter, however, by a maximum dose of oxygen, seem to graduate into the acidifiable group, or at least cease to form salifiable bases.

We shall now delineate a general chart of Chemistry, enumerating its various leading objects in a somewhat tabular form, and pointing out their most important relations, so that the readers of this Dictionary may have it in their power to study its contents in a systematic order.

CHEMISTRY

Is the science which treats of the specific differences in the nature of bodies, and the permanent changes of constitution, to which their mutual actions give rise.t

This diversity in the nature of bodies is derived either from the AGGREGATION or COMPOSITION of their integrant particles. The state of aggregation seems to depend on the relation between the cohesive attraction of these integrant particles, and the antagonizing force of heat. Hence, the three general forms of solid, liquid, and gaseous, under one or other of which every species of material being may be classed.

For instruction on these general forms of matter, the student ought to read, 1st, The early part of the article ATTRACTION; 2d, CRYSTALLIZATION; 3d, That part of CALORIC entitled, "Of the change of state produced in bodies by caloric, independent of change of composition." He may then peruse the introductory part of the article Gas and BALANCE, and LABORATORY. He will now be sufficiently prepared for the study of the rest of the article Caloric, as well as that of its correlative subjects, TEMPERATURE, Thermometer, EVAPORATION, CONGELATION, CRYOMETER, Dew, and CLIMATE. The order now prescribed will be found convenient. In the article Caloric, there are a few discussions, which the beginner may perhaps find somewhat difficult. These he may pass over at the first reading, and resume their consideration in the sequel. After CALORIC he may peruse LIGHT, and the first three sections of ELEC

TRICITY.

The article COMBUSTION, will be most advantageously examined, after he has become acquainted with some of the diversities of COMPOSITION; viz. with the three vitreo-polar dissolvents, oxygen, chlorine, and iodine; and the six non-metallic resino-polar elements, hydrogen, azote, carbon, boron, sulphur, and phosphorus. Let him begin with oxygen, and then peruse, for the sake of connexion, hydrogen, and water. Should he wish to know how the specific gravity of gaseous matter is ascertained, he may consult the fourth section of the article Gas.

The next subject to which he should direct his attention is CHLORINE; on which he will meet with ample details in the present Work. This article will bear a second perusal. It describes a series of the most splen

* I here regard silica acting as a base to fluoric acid, in the fluosilicic compound; but the subject is mysterious. See ACID (FLUORIC).

† I do not know whether this definition be my own, or borrowed. I find it in the syllabus of my Belfast Lectures, printed many years ago. Another definition has been given in the Dictionary, article CHEMISTRY.

did efforts ever made by the sagacity of man, to unfold the mysteries of nature. In connexion with it he may read the articles CHLOROUS and CHLORIC OXIDES, or the protoxide and deutoxide of Chlorine. Let him next study the copious article Iodine, from beginning to end.

Carbon, boron, sulphur, phosphorus, and azote, must now come under review. Related closely with the first, he will study the carbonous oxide, carburetted and subcarburetted hydrogen. What is known of the element boron, will be speedily learned; and he may then enter on the examination of sulphur, sulphuretted hydrogen, and carburet of sulphur. Phosphorus and phosphuretted hydrogen, with nitrogen or azote, and its oxides and chlorides, will form the conclusion of the first division of chemical study, which relates to the elements of most general interest and activity. The general articles Combustible, Combustion, and Safe-lamp may now be read with advantage; as well as the remainder of the article attraction, which treats of affinity.

Since in the present work the alkaline and earthy salts are annexed to their respective acids, it will be proper, before commencing the study of the latter, to become acquainted with the alkaline and earthy bases.

The order of reading may therefore be the following: first, The general article alkali, then potash and potassium, soda and sodium, lithia, and ammonia. Next, the general article earth; afterwards calcium and lime, barium and barytes, strontia, magnesia, alumina, silica, glucina, zirconia, yttria, and thorina.

Let him now peruse the general articles acid and salt; and then the nonmetallic oxygen acids, with their subjoined salts, in the following order:sulphuric, sulphurous, hyposulphurous, and hyposulphuric; phosphoric, phosphorous and hypophosphorous; carbonic and chloro-carbonous; boracic; and lastly, the nitric and nitrous. The others may be studied conveniently with the hydrogen group. The order of perusing them may be, the muriatic (hydrochloric of M. Gay-Lussac), chloric and perchloric; the hydriodic, iodic and chloriodic; the fluoric, Auoboric, and fluosilicic; the prussic (hydrocyanic of M. Gay-Lussac), ferroprussic, chloroprussic, and sulphuroprussic. The hydrosulphurous and hydrotellurous, are discussed in this Dictionary, under the names of sulphuretted hydrogen, and telluretted hydrogen. These compound bodies possess acid powers, as well perhaps as arsenuretted hydrogen. It would be advisable to peruse the article prussine (cyanogen) either before or immediately after prussic acid.

As to the vegetable and animal acids, they may be read either in their alphabetical order or in any other which the student or his teacher shall think fit. Thirty-eight of them are enumerated in the sequel of the article ACID; of which two or three are of doubtful identity.

The metallic acids fall naturally under metallic chemistry; on the study of which I have nothing to add to the remarks contained in the general article METAL. Along with each metal in its alphabetical place, its native state, or ores, may be studied. See ORES.

The chemistry of organized matter may be methodically studied by perusing, first of all, the article vegetable kingdom, with the various products of vegetation there enumerated; and then the article animal kingdom, with the subordinate animal products and adipocere.

The article analysis may be now consulted; then mineral WATERS; equivalents (chemical); and analysis of ores.

The mineralogical department should be commenced with the general articles mineralogy, and crystallography; after which the different species and varieties may be examined under their respective titles. The enumeration of the genera of M. Mohs, given in the first article, will