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factory, that there seems to be little room left for argument. We must say, that to us, the supposed discovery of Berthollet never carried with it any thing like conviction, and we always considered the praises and prizes which were so liberally conferred on it, as so many instances only of the facility with which the world is ready to bestow its approbation on all the performances of a person once celebrated, and frequently even the more enthusiastically the more paradoxical they appear. At the same time we must observe, that the objections of Pfaff are not so immediately applicable to Berthollet's doctrines as they appear at first sight to be; the partition of one substance between two others being principally asserted by Berthollet, as existing in the state of solution, where there is nothing to disturb it; while he considers the crystallization of one of the compounds as a new cause, perfectly capable of modifying the previous arrangement of the substances. What Sir H. Davy attributes to the experiments of Richter and Morveau was sufficiently understood by Bergman, and still more explicitly demonstrated by the contemporary or even earlier experiments of Wenzel. Kirwan's investigations on this subject were well projected, but by no means happily executed. Richter's first work on chemical combinations was published in 1792: his pompous and elaborate essays have all ended in a short and imperfect table of proportions, which has been, in a great measure, superseded by the more accurate researches of Berzelius and other late chemists. Bergman had also made experiments which prove that the oxygen, capable of enabling one metal to form a salt, was sufficient to serve for the oxydation of as much of another metal as precipitated it, and entered into combination with the acid: but it was reserved for Gay Lussac to place this law in a clear point of view, and to establish and illustrate it by decisive experiments. The principles of Berthollet were strongly and successfully opposed by Proust in 1804; he showed that in the combinations of metals with oxygen and with sulphur, certain fixed proportions are always observed in preference to others; his first experiments on the sulphurets were made in 1801. The great improvements in this doctrine, which are incontestably of very modern date, are the establishment of the simplicity of the numbers expressing the proportions of combinations, especially when they relate to the volumes of elastic fluids, or to the comparative relations of subsalts or supersalts, and of their identity in compounds apparently of very different kinds; for example, in salts, sulphurets, and oxyds: and for these facts the science is principally indebted, after Mr. Higgins, to Dalton, Gay Lussac, Smithson, and Wollaston. The results of these principles may be most conveniently compared by exhibiting them in a tabular form; and as no table of this kind is to be found in
Sir H. Davy's work, we shall here take the liberty of inserting such a one, in which we have collected most of the numbers which he has ascertained, together with some others which we have deduced from the experiments of Berzelius and Richter.
Table of the Proportional Weights of Chemical Substances entering into combination.
88 or 44
74' (60?) 77?
' 120' (128 ?)
• 55' (110?)
By means of this table we can at once ascertain the proportions of the component parts of any salt or other compound of the substances contained in it: thus nitre consists of 90 potass and 101 nitric acid, or of 47 per cent. alkali and 53 acid in its dry state: or if we consider the white caustic potass, in the driest state in which
it is exhibited by any common means, when it is still a hydret, and contains a portion of water, expressed by 17, the number for potass will become 107; and the number for the most concentrated liquid nitric acid, becoming in a similar manner 118, the proportion of alkali will be about 47 per cent. instead of 47. And in a similar manner we find for the sulphate of barita 145 and 75, or 66 per cent. of earth, and 34 of dry acid, which is a result fully established by the most accurate analyses. It must, however, be observed, that the number here assigned to the carbonic acid is that which belongs to the alkaline subcarbonates, which are not, strictly speaking, ucutral salts; and that there are some other apparent irregularities, of the same nature, in the operation of the laws of simple proportions.
Besides the general doctrines which we have thus particularly examined, there are many detached passages, which we shall think it right to mention in the order of their occurrence; some on account of their novelty and interest, others because, in a work so likely to be universally studied, we wish to leave nothing unnoticed, which appears to require either correction or explanation.
In speaking of Aristotle, (p. 5,) our author seems rather to have been led away by a popular clamour, than to have studied with attention the real tenour of that great observer's mode of philosophizing. The practice of advancing general principles, and applying them to particular instances,' is so far from being fatal to truth in all sciences,' that, when those principles are advanced on sufficient grounds, it constitutes the essence of true philosophy; and Aristotle did not advance principles on physical subjects without what he thought sufficient grounds. The beauty of the theory of gravitation depends wholly on the establishment of a general principle, and its application to particular instances: and even our .author appears to have applied the general principle of simple proportions to particular instances, almost in contradiction to his own earlier rescarches; where, for instance, he doubts the accuracy of his experiment with diamond and potassium, because it' does not harmonize with the doctrine of definite proportions.' (p. 312.) In the case of ammonia, too, he has, perhaps, been partly induced by similar considerations, to repeat his former analysis, in which he 'thought that a small quantity of water was found,' and 'very delicate experiments' having convinced him (p. 269) that no water is obtained, he has very candidly returned to Mr. Berthollet's opinion respecting the constitution of this substance.
P. 69. For any thing we know to the contrary, gravitation and cohesion may be mere modifications of the same general power of attraction.' This is a mistake not altogether uncommon with those who have not sufficiently attended to the mathematical characters
of the forces concerned. Whether or no these forces may be produced by any different modifications of the same cause, we have no right even to conjecture; but their magnitude and the laws of their action are so totally dissimilar, that they cannot possibly be considered as modifications of the same power.
P. 70. There is an error in the comparative expansions of solids and fluids as here related: 100,000 parts of glass, raised from the degree of freezing to that of boiling water, became 100,083;-the expansive power of liquids in general is greater than that of solids, -100,000 parts of mercury become 101,855,' that is, in bulk; but 100,000 parts of glass become in bulk 100,250, not 100,083 only; and 100,000 of zinc 100,910, its expansion being about half as much as that of mercury, instead of one-sixth, as would be inferred from our author's statement. P. 75. A common thermometer,' is not hermetically sealed' at the moment of the ebullition of the mercury;' for, in this case, the fluid would sink within the bulb at all common temperatures, unless the tube were much longer than usual.
P. 76. Professor Leslie has complained, in the public papers, that Sir H. Davy mentions a thermometer of Van Helmont, as similar to his differential thermometer, while, in fact, Van Helmont's instrument was open at one end; although his explanations 'incidentally involved the principle of the differential thermometer, which the author never once dreamed of reducing to use:' nor has the truth of this statement been disproved by the person who has replied on behalf of Sir H. Davy. The principle of the differential thermometer' is too simple to be called an invention; and it is only by its ingenious application that Professor Leslie has made it an object of attention.
P. 79. A very amusing experiment, in which ether, floating on water, is made to burn, without sensibly elevating the temperature of the water one-eighth of an inch below the surface, is adduced as a proof of the great difficulty with which fluids transmit heat downwards. But it must be remembered that liquid ether is not susceptible of a temperature higher than 102°, and that a feverish hand, held at the surface of the water, would heat it just as rapidly as the boiling ether; and probably much more so, since the capacity of ether for heat is less than half of that of an aqueous fluid.
P. 80. In solids the attractive force predominates over the repulsive; in fluids and in elastic fluids they may be regarded as in different states of equilibrium.' It is difficult to conceive how so much error and confusion could have been collected, by such an author, into so short a sentence. When one of two forces' predominates,' there must be motion, and the parts of a body cannot remain at rest: indeed so far is the attractive force from predomi
VOL. VII. NO. XV.