supposing the accession of heat to have gone on above 212°, at the same rate as before the water boiled, it was estimated that the quantity of heat thrown into the steam was not less than 800°. The amount of heat rendered latent therefore was the difference between 212o and 800°, or 588°. Indeed, from experiments made on the condensation of steam, it appears that the quantity of heat rendered latent by the vaporization of water, exceeds considerably the statement now made; amounting to more than 900°.

This discovery was rich not only in sublime views relative to the economy of nature, but also in a great variety of practical uses. A new instrument was placed in the hands of man, by means of which he acquired a command over the opposite qualities of heat and cold. Art was enabled to advance into a province which appeared the most rigorously prohibited to her approach, and to assume the controul of physical causes which seemed the farthest removed from her influence. The production of ice, and even of an intenser degree of cold than nature herself has yet exhibited, is placed within the reach of every novice in chemistry; whilst the delicacies of the table and the comfort of our chambers have derived some of their highest improvements from the same

source.

Pneumatic chemistry was destined to receive a great addition to its stores from the active hands of Dr. Priestley, In his various experiments on fixed air, as carbonic acid gas was then called, and on air tainted by combustion and respiration, he occasionally brought to light some very interesting facts; but the most brilliant of his achievements, and that on which his fame will mainly rest with posterity, is the discovery of oxygen gas. It was in the year 1774 that he was conducted in the course of his researches to this fortunate result; and Dr. Rutherford had two years before detected in the air of the atmosphere the existence of azote, or nitrogen, so that the composition of the invisible fluid which invests our globe was no longer concealed from the curiosity of science.

The path opened up by Black and Priestley was sedulously occupied by Bergman, Scheele, and Cavendish; the second of whom has derived an accession to his fame from the discovery of oxygen, at the same time with the philosopher of Birmingham. Lavoisier, indeed, claimed the same honour; alleging that he had attained to the knowledge of that gas simultaneously with Scheele a point in scientific history which still remains undetermined, and which has been a good deal perplexed by national jealousy and personal am

bition. Scheele also discovered oxymuriatic acid, which has since been called chlorine: and made besides a great va riety of new combinations in metallic and gaseous, sub

stances.

The name of Cavendish is chiefly celebrated for the discovery of hydrogen and the decomposition of water. He was a man of uncommon modesty, approaching even to dif fidence, and a true lover of science for its own sake. He was, says Mr. Brande, an enemy to the new nomenclature of chemistry, and was fond of foretelling its downfall. He disliked all innovations that were not rendered absolutely necessary by the progress of experiments, and would never adopt new opinions till fully and leisurely convinced of the fallacy of the old ones. "Though occasionally in his com pany I scarcely ever knew him take a part of a continued dialogue, except at the Royal Society Club, where he dined every Thursday, till within a short time of his death: and there he never spoke except to gain or give information."

We are arrived at the era of Lavoisier, the great reformer of chemical language, and the first who established the antiphlogistic system on a firm and durable basis. Priestley continued till the last to oppose the progress of those sound views on combustion which were originally suggested by the reasonings of Rey, and confirmed by the experiments of Hooke and Boyle; and notwithstanding the luminous principles evolved by Black, Bergman, Scheele, and Cavendish, it was reserved for the French school to construct such a theory, as would reconcile all opinions and give a consistent explanation of all phenomena.

It is extremely difficult in most cases to appreciate exactly the merit of invention, as it is impossible to know what hints and aids have been administered to the inventor; how much he owes to regular scientific research; and how much is to be ascribed to mere accident, where the result had neither been sought nor conjectured. In regard to Lavoisier, however, we are supplied with the means of measuring his services in chemistry; and we agree in opinion with Mr. Brande, that, if taken in connection with the labours of the old English school, the experiments of Hooke and Mayow, and the discoveries of Black, Priestley, and Scheele, these services have been greatly over-rated. Lavoisier, as Mr. B. aptly observes, though a great architect in the science, laboured little in the quarry; his materials were chiefly shaped to his hand, and his skill was displayed in their arrangement and combination.

We have no intention, however, to depreciate the knowledge and ingenuity which Lavoisier carried to his great work, the formation of a nomenclature on a scientific and uniform plan. Time and the progress of discovery have, indeed, proved that the undertaking was premature; but the merit of this distinguished chemist and his coadjutors remain undiminished, and the general principles of their scheme admit of an adaptation to the most improved state of the science. It was only from a man deeply conversant with the chemical properties of matter that the following anticipation could proceed in reference to the nature of the alcaline earths, which at that time, were regarded as simple bodies. From certain phenomena which he had just recorded, he views it as probable that oxygen is the bond of union between metals and acids, and from this we are led to suppose, that oxygen is contained in all substances which have a strong affinity with acids.

"Hence," says he "it is very probable that the four eminently salifiable earths contain oxygen, and that their capability of uniting with acids is produced by the intermediation of that element. What I have formerly noticed relative to these earths, namely, that they may very possibly be metallic oxides, with which oxygen has a stronger affinity than with carbon, and consequently are not reducible by any known means, is considerably strengthened by the above consideration."

It is unnecessary to remark that the achievements of Sir H. Davy in the laboratory of the Royal Institution, have completely verified this anticipation.

The next step, we think, in the history of chemical discovery is that to which we have just alluded. The galvanic pile in the hands of Volta had led to some very striking results, and excited all over Europe the greatest curiosity and expectation in regard to the powers of the new instrument; when, by the aid of that liberal munificence which has always characterized the inhabitants of this great city, Sir. H. Davy was enabled to institute experiments on a very extensive scale, and to produce effects which astonished the world. The decomposition of the alkalis, and the alkaline earths revealed to the chemist a complete set of new principles, both in regard to the mutual agencies of bodies, and the nature of the power by which that agency is maintained. Chemical affinity appears identical with electrical energy; to the extent at least of the fact that the latter controuls and even dissolves the former, and that, too, in substances held

together by the strongest affinities known to the science. The foundation of the old system is entirely shaken. Oxygen, instead of being in all cases an acidifying principle is found to combine with a metallic base and to form an alkali; and heat, so far from being in every instance the effect of a combination between that gas and a combustible substance, is found on many occasions, to be the result of mere chemical action without any absorption of the acidifying principle whatever.

The latest improvement in the science of chemistry, and one which promises very important results, is connected with the discovery of that law which in chemical combinations, regulates the proportions of the combining substances. When two bodies unite so as to form one compound only, that compound always contains the same relative proportions of its component parts: and in cases where two bodies unite in more than one proportion, the second, third, or fourth proportions are multipliers or divisors of the first. For example, carbonic acid unites to potassa in two proportions, and forms two definite compounds. In the one 70 parts of potassa are combined with 30 of carbonic acid; in the other 70 of potassa are united with 60 of carbonic acid. Lead, again, combines with oxygen in three proportions: the first compound consists of 100 lead and 8 oxygen; the second of 100 lead and 12 oxygen; and the third of 100 lead and 16 oxygen. It is deserving of remark, too, that whilst the potassa combines with carbonic acid in the proportions of 30 and 60, it will not enter into combination in any intermediate proportions. The same rule also applies to gaseous bodies. Thus, for instance, nitrogen combines with oxygen in the following proportions, constituting five different compounds.

Results of this nature having been generalized by several authors, particularly by Dalton, Berzelius, Davy, Wollaston, and Dr. Thomson, are known to modern students as the doctrine of "Atomic Theory," or as the "Theory of Definite Proportionals." The fullest account that we have any where seen of this interesting branch of chemical science is to be found in the Annals of Philosophy: a journal which was at

one time very ably conducted by the last of the writers whose names we have just mentioned, and which was particularly valuable as a well digested record of the progress of discovery at home and abroad.

Having finished this outline of chemical history, which contains the mere fastigia rerum from the days of the alchymists down to the discoveries of Davy, and the speculations of Berzelius, we at length find ourselves at the commencement of Mr. Brande's Manual; which professes to teach the principles of the science as they are at présent held by the most approved authors in England and France; and to illustrate them too by well-chosen experiments, the greater part of which may be performed in a private chamber. In justice, then, to this popular writer, we are happy to assert that a beginner could not find a more suitable work for expounding the rudiments of chemical knowledge than that now before us; and also that those who have made the greatest progress in the science will derive much satisfaction from perusing the lucid commentaries on its most abstruse doctrines with which these pages abound, and more particularly from the felicitous application of experiment, wherever the ideas are likely to become confused, or the mutual agency of bodies is in danger of not being clearly perceived. The various methods too, here explained of procuring chemical products, and of preparing them for the manipulations of the laboratory, cannot fail to be extremely useful as well as entertaining to the amateur chemist; and in this respect we know no elementary work, which, combining science with practical details, will bear a comparison with Mr. Brande's Manual. We wish, indeed, that he would be content to forego those rhetorical ornaments, which at the best appear very questionable in a scientific performance, and which in his case so often seduce the imagination, without imparting any light to the understanding. In other respects, his zeal to please urges him on in the proper path. His dexterity as an experimenter cannot be too highly praised; and one never fails to sympathize with him in that honest triumph which accompanies the successful display of professional knowledge, through the medium of a splendid and ingenious apparatus..