and on the peculiar elective attraction of the latter to the oxygen of the air, by M. Berger, of Geneva. We may just add, in this place, that, by stagnation over water, hydroge nous gas is reduced to the state of common air; and, by longer continuance, becomes azotic gas.---But to return to the article before us.

In combining carbonic acid gas with water, our author found that the quantity of the residuum greatly lessened the dissolvent power of the latter, and that a greater proportion was dissolved in a given quantity of water, when the quantity of the air, exposed to it, was increased. The increase of the proportion of the latter appeared more effectual than the increase of temperature. Of sulphurated hydrogen gas, 100 parts of water, at a temperature of 55, absorb 86 parts; of nitrous oxyd at 45°, 100 cubic inches take up from 50 to 54. Azotic gas, as M. Berger has also shown, is scarcely soluble; but our author represents hydrogen gas as less so.

The results of a series of at least fifty experiments, on carbonic acid, sulphuretted hydrogen gas, nitrous oxide, oxygenous and azotic gases, with the above apparatus, establish the following gcneral law, that, under equal circumstances of temperature, water takes up, in all cases, the same volume of condensed gas as of gas under ordinary pressure. But, as the spaces occupied by every gas are inversely as the compressing force, it follows, that water takes up, of gas condensed by one, two, or more additional atmospheres, a quantity which, ordinarily compressed, would be equal to twice, thrice, &c. the volume absorbed under the common pressure of the atmosphere. By frequent repetition of the experiments, I obtained results differing a little from the general principle above stated; but, for all practical purposes, I apprehend, the law has been announced with sufficient accuracy.' P. 41.

In the Appendix, Mr. Henry corrects his former measures; and, of the sulphurated hydrogen gas, states the quantity ab sorbed by 100 measures of water, at 106 and 109; and of nitrous oxyd 86, at 60°. Of the quantities absorbed by gases which have less affinity to water we shall add the proportions from his corrected table.

Table shewing the Quantity of each Gas absorbed by 100 Measures of Water, at 60°.

IV. Experiments and Observations on the various Alloys, on the specific Gravity, and on the comparative Wear of Gold. Being the Substance of a Report made to the Right Honourable the Lords of the Committee of Privy Council, appointed to take into Consideration the State of the Coins of this Kingdom, and the present Establishment and Constitution of His Majesty's Mint. By Charles, Hatchett, Esq. F.R.S.'

This is a laborious and very valuable paper, the joint work of Mr. Cavendish, the Newton of modern times, and Mr. Hatchett, drawn up by the latter. We can give no account. of it adequate to the merit it possesses, but shall notice the chief results.

The object was to ascertain the state of our present gold coin, and to inquire into the loss which it appeared to have sustained by wear within certain periods. ·

·

Two questions were to be principally decided,

1st. Whether very soft and ductile gold, or gold made as hard as is compatible with the process of coining, suffers the most by wear, under the various circumstances of friction to which coin is subjected in the course of circulation?

2dly. Whether coin with a flat, smooth, and broad surface, wears less than coin which has certain protuberant parts raised above the ground or general level of the pieces?

Concerning the first question, opinions were various, and the most intelligent persons were uncertain whether very soft or hard gold was to be preferred; and, in respect to the second question, it must be observed, that although the prevalent opinion was in fa vour of flat and smooth surfaces, yet, as the fact had never been fully and satisfactorily determined, this opportunity was embraced, in order that every doubt might be removed.'

P. 44.

In this inquiry, they first examined the effect of different alloys; and, from their experiments, have added considerably to our metallurgic knowledge, correcting, at the same time, numerous errors. In general, it appeared that the alloys were separable by fusion; that arsenic, which, on account of its volatility, cannot be easily united with gold, is not only carried off by continued heat, though in a small proportion, as it possesses a strong affinity to gold, but that some portion of the gold escapes with it in vapour. With silver, copper, and tin, there was no loss by fusion; with lead, iron, and bismuth, there was a loss, in consequence of calcination or vitrification; with antimony and zinc, chiefly by volatilisation. Tin, in a small proportion, does not make gold brittle, as has been supposed; but two metals only were found suitable as alloys, viz. silver and copper; for gold is changed both in colour and ductility by the necessary admixture of the others. With respect to the diminution of ductility, the different metals seem to act in the following order.

The various incidental remarks would detain us very long. We may, however, remark that we were considerably instructed by what our author has observed respecting the different kinds of copper.

The second section is on the specific gravity of gold, when alloyed by different metals. We may premise some observations suggested by the introduction to this section. The spe cific gravity of a compound is not always that which may be supposed to result from the respective densities of the ingredients. It is sometimes less, owing to the little cavities, or airbubbles; and this inconvenience, except in the brittle metals, may be remedied by rolling or hammering. Yet it is different from another cause, which we are anxious to point out. The union is very often, we dare not say always, a chemical combination: the result is a third body, different from either of the component parts, and its internal organisation may be supposed to differ also from either. In the passage of every body from a state of fluidity to solidity, there is a crystallisa tion more or less regular, as the cooling has been slower or quicker; and, probably, the arrangement of its crystalline forms may greatly influence the specific gravity of the new body. Thus, it is singular that lead and bismuth with gold, or with copper and gold, produce a mixt metal, similar in specific gravity and some other properties, though lead and bismuth differ so materially from each other. One cause of the great uncertainty in the result of trials respecting the specific gravity of combined metals, is the difficulty of uniting the alloy equally through the whole mass. Even in philosophic experiments, great accuracy in this respect cannot be obtained; and an allowance is made for this inconvenience at the mint. In casting, also, there is a considerable inequality, for

* Had the platina been quite pure, the compound metal would probably have possessed more ductility; I cannot therefore take upon me to assert positively, that the place here assigned to platina, is precisely that which it ought to occupy.'

CRIT. REV. Vol. 1. January, 1804.

D

the densest part of the ingot is at the bottom; so that a bar may, at each end, be of the same specific gravity, though of different value; for the finer quality of the upper extremity may be compensated by the superior density of the lower. The specific gravity is also increased by rolling, and diminished by annealing, as well as by friction. The last circumstance is singular, and little to be expected. The specific gravity of gold, made standard by silver or copper, or by both united, may vary nearly from 18 to 17.

The third section is on the comparative Wear of Gold, alloyed by different Metals.' We cannot analyse it more satisfactorily than the author has done in his own summary.

From a general view of the present experiments, there does not appear to be any very great or remarkable difference in the compa rative wear of the three kinds of standard gold, all of which suffer abrasion slowly, and with much difficulty; and (as it has been already observed) the difference of wear between the two last mentioned, is certainly but inconsiderable. For these reasons, and from the consideration of every other circumstance, it must be evident, that the extraordinary loss which the gold coin of this kingdom is stated to have sustained within a certain limited time, cannot, with even a shadow of probability, be attributed to any important defect in the composition or quality of the standard gold; and all that can be said upon this subject is, that some portion of this loss may have been caused by the rough impression and milled edge now in use, by which, each piece of coin acts, and is acted upon by the others, in the manner of a file.

The loss thus occasioned cannot however be considerable; for the quality of the present standard gold is certainly that which is well adapted to resist abrasion, especially in the case of the friction of coin against coin; and this is strongly corroborated by the observations of bankers and others, who are in the habit of sending or receiving large quantities of gold coin from any considerable distance. When a number of guineas, rather loosely packed, have been long shaken together by the motion of a coach or other carriage, the effects of friction are observed chiefly to fall upon only a few of the pieces. But it is not a little remarkable, that although these are often reduced nearly or quite to the state of plain pieces of metal or blanks, yet, upon being weighed, they are found to have sustained little or no loss; and from this it appears, that the impressions have been obliterated, not by an actual abrasion of the metal, but by the depression of the prominent parts, which have been forced into the mass, and become reduced to a level with the ground of the coin. Pieces of hard gold would not so easily suffer by depression; but the real loss would probably be greater, they being, in the case of the friction of coin against coin of similar quality, more susceptible of abrasion.

Upon the whole, there is every reason to believe, that our gold coin suffers but little by friction against itself; and the chief cause of natural and fair wear probably arises from extraneous and gritty

particles, to the action of which the pieces may occasionally be exposed in the course of circulation. But still it must be repeated, that the united effects of every species of friction to which they may be subjected, fairly and unavoidably, during circulation, cannot produce any other wear than that which is extremely gradual and slow, and such as will by no means account for the rapid diminution which has been observed in the gold coin of this country.' P. 190.

great and

'V. Observations on the chemical Nature of the Humours of the Eye. By Richard Chenevix, Esq. F.R.S. and M. R.I.A.' This, which may be styled one of the minor subjects of physiologic consideration, has not been yet satisfactorily examined; and fancy must have given the aqueous humour something of an ethereal nature, when Bertrandi determined its specific gravity to be 975, in other words, less than that of distilled water. In the eyes of sheep, at 60° of Fahrenheit, the aqueous humour is 10090; and it contains, in very minute proportions, albumen, gelatine, and muriat of soda, dissolved in water. The specific gravity of the crystalline is 11000, but it contains no salt. The albumen and gelatine is united with a less proportion of water. As it putrefies rapidly, it must contain a large portion of animal matter, or azote, which our author has not noticed. The vitreous humour is said, in every respect, to resemble the aqueous. The result of the experiments on the humours of the human eye was the same; but the specific gravity of the aqueous and crystalline humours was 10053 and 10790 respectively; in the eyes of oxen 10088 and 10765.

What is particularly worthy of notice is, that the difference which appears to exist between the specific gravity of the aqueous or vitreous humour and that of the crystalline, is much greater in the human eye than in that of sheep, and less in the eye of the ox. Hence it would appear, that the difference between the density of the aqueous and vitreous humour and that of the crystalline, is in the inverse ratio of the diameter of the eye, taken from the cornea. to the optic nerve. Should further experiments show this to be a universal law in nature, it will not be possible to deny that it is in some degree designed for the purpose of promoting distinct vision.' P. 198.

The cataract is owing, in our author's opinion, to the coagulation of the albumen in the crystalline; and, from its connexion with gouty habits, he seems to suspect that the phosphoric acid may have some effect. On the whole, however, this analysis is, in many respects, imperfect; and we wish the author, of whose chemical abilities we have formed an advantageous idea, would resume the subject. Let us only remark, among many observations we might make, that the vitreous humour must differ, in some respects, from the aqueous, and