Helmont, however. must be allowdiscover of gaseous, or aeriform bodies; for ? was called a magician, and .. imprisoned by tribunal ion.

Dr. Hook proved, 1. That air in which we live, move, . breathe, is the universal solvent of does not perform this action tali body be first sufficiently heated; 3. That this process of dissolution generates a very great heat, or what is called fire ; 4. That light also produced from this action ; 5. That these phenomena do not arise from the air itself as ment, but from that part of the air which is inherent in it, and is like, if not the vary . which is fixed in salt-petre. Thus find that the foundation was laid for the subsequent discoveries of BOYLE, MAYOW, and HalES first ascertained the exact quantity of air, or an elastic fluid to air, either produced or absorbed by the burning of sulphur, or of candles, or by the respiration of animals. Hence, the last mentioned philosopher compares the air to "a true Proteus, now fixed, now volatile, entering into the com-position of bodies, where it exists in a solid form, deprived of elasticity, and of those rues which formerly distinguished it., addin gravity to these bodies, and under certain circumstances, alone capable of recovering its elasticity, and becoming again an elastic, thin fluid, and therefore well deserving to be adopted among chemical principles, and to possess a rank which has hitherto been denied it." In his admirable work, entitled Vegetable Statics, we perceive the first traces of the existence of air in those waters called acidulous; and he not only remarked that they contain four or five times more air than common water, but also conjectur-ed, that they owed to it their sparkling and briskness. The truth and practical application of this discovery to medical purposes, were vigorusly enforced by the immortal Boerhaave, whose reputation, both as a physician and a philosopher (two great qualifications, not always united), had resounded to the remotest parts of the globe.— Previous to his time, the illustrious Bechee first began to collect and compare the immense store of che-mical facts, and arrange their relations towards a new system. Persecuted and despised, like, most benefactors of mankind who forsake the beaten track, he fled from his native country, retired to England, and died of a broken heart at London in 1682. His theory, however, was adopted by the sagacious and intrepid Stahl, then first physician to the King of Prussia. In the opinion of these two authors, fire enters into the composition of ail inflammable bodies, into metals, and most minerals ; and in that condensed and fixed state, they called it phlogiston, or latent fire, to distinguish it from its condition, when in a free state. They farther believed that phlogiston is actually a material body, .

liable to be modified and influenced by circumstances; and that consequently all metals were compounds; and water, as containing no phlogiston, a simple body. Although this vague theory has been strenuously maintained by nearly all the chemists of Europe, for upwards of a century, and is still supported by Dr. Priestley, and many of his followers in this and other countries, yet, to the honour of our age, and we venture to say, the credit of that voluntary exile, the doctrine of phlogiston is nearly exploded. To proceed in this explanation, according to the order of time in which the leading fads were ascertained, we shad first mention, that Dr. Black, our late illustrious professor of chemistry, in the University of Edinburgh, about the middle of last century observed, that certain substances, such as marble, chalk, and limestone, when submitted to the process of fire, lost half their former weight: and, when treated with acids, the compound weighed less than before. Hence, it became evident, that something was lost; and, from a strict chemical analysis, he proved this something to be a permanently elastic fluid, which he termed fixed air - deprived of which, the residue was caustic, or quick-lime, capable of corroding all animal and vegetable substances. Hitherto, the existence of fixed air, and its combination with bodies, was only conjectured, and no philosoper, since VAN-Helmont's time, had adopted this opinion. Thus, new views were opened in the examination of all matter, and the attention of experimental inquirers was principally directed to the decomposition of solid bodies. Dr. RutheRFORd extended this inquiry, and deter-mined the difference between fixed and azotic air. another species of tive gas, which cannot be by animals, nor is it misci-ble- with water, and therefore by-some called mephitie, or phlog cated air. This azotic air constitutes about seventy-two parts in hundred of the common atmosphere, and therefore deserves • ticular attention : it was discovered by Dr. Priestley, and arises from the changes which atmospheric air undergoes in every process of combustion, putrefaction, and respiration; in short, it is of the same nature as that contained in the air-bladder of the carp, and other fish. Being much lighter than the air of the atmosphere, the azote instantly extinguishes burning tapers, and rapidly destroys the life of animals immersed in it.

The most splendid and important discovery of Dr. Priestley, however, is that of vital air, or oxygen, to which he was accidentally led, in August 1774, and which transmit his name to posterity This aerial fluid, which he deno-urinates dephlogisticated air, because he supposed it to be deprived of all its phlogiston, also forms a considerable part of our atmosphere, so that it has been a tinned, by experiment, to exist there in the proportion of about 27 or 28 parts in 100. Thus, the composition of that boundless element in which we breathe and move, was, at length, discovered, and though Bergmann and Schfele, in Sweden, as well as Lavoisier, in France, claimed an equal or coeval merit with Dr. Priestley, having, about the same period, in their experimental researches on this subject, observed similar' yet we behave, the last mentioned philosopher is justly entitled to the honour of being called the author of this great discovery. The manner in which it was made, is foreign to our purpose; and we shall fore briefly state, that the ingenious and noble Lavoisier, who fell a sacrifice to the ambition and tyranny of Robespierre, of infa-mous memory. established a new system of chetry upon the ground-work of this contested discovery, by which the component parts of the atmosphere were clearly and indubitably determined. In contradistinction to the exploded doctrine of phlogiston, the theory adopted by Lavoisier, and supported by Berthollet, Morveau, AdeT, Has SENFRATZ, De LA PLACE, Monge, Chaptal, Foukcroy, and others, was now termed the Antiphlogistic System. The principal feature of new French system is, that the is compound body, and that metals, in general, are simple sub-nces. We cannot, in this place, enter into farther particulars ; and therefore only recommend to the juvenile reader, the perusal and study of such elementary works afford a plain and accurate explanation of that admirable and highly science; without a compe-: knowledge of Which, he will 11 in a state of infancy, at least with respect to the numberless phenomena taking place in the physical world We regret, however, that a publication calculated completely to the expectations of an ordinary reader, a still a desideratum though there have been published within the last twenty years, a great variety of instructive books on this subject.

The principal difficulty appears to arise from the unsettled state of* chemical nomenclature, which has lately been, in a great measure, removed by the praise-worthy labours of Dr. Pearson, Dr. Dick-son, and Mr. Parkinson ; whatever merit these introductory works may posssess, there is still wanted a concise, perspicuous, and systematic analysis of the science of chemistry, such as could be read, with satisfaction, by every person possessed of ordinary talents. Tanner and Scherer in Germany, have attempted works; but their manuals abound in too abstract propositions, and are written in a doge rather than narrative style, that may tend to entertain the reader, and imperceptibly lead from the more simple to connected propositions Although it be perfectly consistent with .scientific arrangement, to begin the explanation of a system general truths, and then de-nd to particulars; yet we incline to think, that the young students, as well as readers in general, would acqaire a more correct idea of a subject, by commencing the series of principles with such illustrations, as would render very term, involved in the first definition, perfectly clear and familiar to their understanding . Thus, the immortal BACON was peculiarly happy in defining simple ideas, before he proceeded to reduce them at heads, and draw the or exhibit the result, by the most unequivocal process of induction. Instead, however, of following the footsteps of this mighty genius, most of our modern physical writers, either begin the analysis of the subject with gene-maxims ; or they dissect an divide the whole into distintl paris and fatigue the reader with en repetition, without affording him view of the synthesis ture of members (if that expression be allowed), which alone could enable him to connect the several causes and effects, of which the whoe is composed. In justice, however, to Lavoisier, the foun-der of the new system, we shall observe, that his "Element* of Chemist/y" possess, in this respect, uncommon merit; though he dwells too long upon the rationale, without exemplifying the principles, in such a manner as to impress the mind with sensible objects, which alone can perma-nently fix the idea, and connect every link of the proposition, claim the indulgence ice of our readinvoluntary digression ; and though we cannot, in truth, exclusively recommend any late work, published in the form of a popular, or familiar introduction; chemistry, yet we shall mention several valuable treatise?, that have successively appeared, and are titled to attention. The different translations from the French of Lavoisier, Chapital, and Four-: croY, and eg that of the by "Mr. John Thomson, deserves to be read, and diligently studied 3 that from the German of Professor Gren, is likewise a work of merit, for professional readers ; and among the original English works, we shall point out Dr. Higgins's "View of the phologistic Antiphlogistic Theories" (8vo. 7s.) Mr. Nicholson's " first Principles 0f chemistry (8vo. 6s. 6d.); and Dr. Garnett's "Outlines of Lectures of Chemistry (8vo. 4s.) ; besides there are veral smaller tract;, among which we remember, with satisfaction, the perusal of that written by Mr. Henry, of Manchester.