ftruction from it. The language is plain and forcible; fometimes incorrect, but always perfpicuous. The nature of the fubject will not permit us to enlarge on it fo much as its real merit would otherwife have allowed; we shall therefore only observe, that if the author fometimes pursues the views of his predeceffors, inflead of cenfuring the want of novelty, we should value his observations, in confirmation of the established practice, as thofe of a candid and intelligent phyfician. If the fimplicity of his plans fometimes furprife, we should attend to his own requeft, and give them a fair trial. It will be obvious, from the judgment of his remarks on what was before known, that we ought to place fome confidence on what he

recommends.

cure.

Dr. Swedia'r has added a very extenfive fynopfis of the different preparations of mercury, in which he informs us of the nature of fome remedies which have been hitherto concealed. The observations which are added to them are judicious and ufeful. He fpeaks with refpeft of the pulvis mercurii cinereus, in the laft edition of the Edinburgh Pharmacopeia, as the mildest of the faline mercurial preparations; and feems to think that the reputation of the corrofive fublimate arifes rather from the facility with which it at first relieves troublesome symptoms, than its efficacy in completing the The terre feuilletée mercurielle of Monf. Preffavin, is the mercury combined with cream of tartar; and Keyfer's pills confift of the fame metal with the acetous acid. We take this opportunity of remarking, that the method of uniting mercury with the vegetable acids, which has been much boasted of, and which we daily expect to fee recommended with fome parade, is by no means new or difficult. It was long ago known that mercury, deprived of its phlogiston, had a very different affinity from what it poffeffed when combined with this principle; and this peculiarity was applied to the formation of milder mercurial falts many years fince. hydrargyrum acetofum is compofed of a folution of mercury in the nitrous acid, combined with the fal diureticus; from which, by means of the double elective attraction, two new compounds are produced. The importance of calomel, and the difficulty of procuring it finely powdered, renders the following process of very great confequence; we have therefore little doubt but that it will be acceptable. It is taken from the Stockholm Tranfasions, and invented by Mr. Scheele.

The

Half a pound of quickfilver, and the fame quantity of pure aqua fortis, and to be put into a small veffel with a long neck, the mouth of which is to be covered with paper. The

.

veffel is then to be placed in a warm fand-bath; and after a few hours, when the acid affords no figns of its acting any longer on the quickfilver, the fire is to be increased to fuch a degree that the folution may nearly boil. This heat is to be continued for three or four hours, taking care to move the veffel from time to time, and at laft the folution is to be fuffered to boil gently for about a quarter of an hour. In the mean while we are to diffolve four ounces and a half of fine common falt in fix or eight pints of water. This folution is to be poured boiling into a glafs veffel, in which the abovementioned folution of quickfilver is to be mixed with it, gradually, and in a boiling ftate alfo, taking care to keep the mixture in conftant motion. When the precipitate is fettled, the clear liquor is to be drained from it, after which it is to be repeatedly washed with hot water till it ceafes to impart any tafte to the water. The precipitate obtained by this method is to be filtered, and afterwards dried by a gentle heat.

It might be fuppofed, that when the nitrous acid ceases to effervefce with the mercury, it is faturated with it: but this is far from being the cafe; the acid, when the heat is increased, being still able to diffolve a confiderable quantity of it; with this difference, however, that the quickfilver at the beginning of the procefs is calcined by the acid, but afterwards is dif folved by it in a metallic form. In proof of this we may obferve, that not only more elastic vapour arises, but also that by adding either fixed or volatile caustic alkali we obtain a black precipitate; whereas, when the folution contains only calcined quickfilver, the precipitate becomes yellow by fuch an addition, If this black precipitate is gently diftilled, it rifes in the form of quickfilver, leaving a yellow powder, which is in fact that part of the mercury that in the beginning of the operation was calcined by the nitrous acid.

The boiling of the folution for about a quarter of an hour is neceffary, in order to keep the hydrargyrum nitratum in a diffolved ftate, it being much difpofed to chryftalize. In ge neral, fome of the mercury remains undiffolved; but it is al ways better to take too much than too little of it, because the more metallic fubftance the folution contains, the more mercuriús dulcis will be obtained.

"It is neceffary to pour the mercurial folution into the folution of falt by a little at a time, and cautiously, so that no part of the undiffolved quickfilver may pafs along with it. Two ounces of common falt are fufficient to precipitate all the mercury; but then it may easily happen that fome fuperfluous mercurius corrofivus attaches itfelf to this precipitate, which the water alone is incapable of feparating completely. This is undoubtedly the reafon why mercurius præcipitatus albus is always corrofive. I have found that common falt poffeffes the fame quality as fal ammoniac, viz. that of diffolving a great quantity of mercurius corrofivus. I therefore employ four

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Ounces

J

ounces and a half of common falt in order to get the mercurius corrofivus entirely feparated.'

The remainder of the extract from Mr. Scheele, confifts only of proofs that this fubftance is really calomel, and the rationale of the process. We have abridged it, fince it was too long for our Journal.

J

As we have already given our opinion in general of the work, and produced fome fpecimens of the industry of the author, we shall now leave him to enjoy the reputation which he feems to have deferved. Yet we ought to add, that he thinks the disease not the production of America; and obferves that this opinion will be rendered more probable, from the light thrown on it by Dr. Hensler, from old authentic manufcripts difcovered by him.'

Elays on the Effects produced by various Proceffes on Atmospheric Air; with a particular View to an Investigation of the Conftitution of the Acids. By M. Lavoisier, Member of the Royal Academy of Sciences at Paris, &c. Tranflated from the French, by Thomas Ilenry, F. R. S. 8vo. 2s. 6d. Johnson. WE with rather to announce this publication, than to give

any decided opinion on it, fince it tends to produce a very confiderable revolution in our opinions relative to the conftitution of some chemical elements. Much injury has been done to this branch of chemistry by hasty opinions and extravagant, or injudicious commendations. Principles, which have an extenfive influence, fhould therefore be weighed with caution and deliberation; for, if the errors are widely diffeminated, the branches acquire an independent existence, and ftill flourish, though the original trunk be deftroyed. The reputation of our author prevents us from fufpecting any wilful mifreprefentations; and the experiments appear to us to be planned with judgment, and conducted with addrefs. Our philofophical readers do not want to be informed of Dr. Priestley's opinions on these subjects; we shall not therefore extend our article, by recapitulating where they differ from thofe of Mr. Lavoifier, but give a concife and comprehenfive account of the fubject of this little volume.

Mr. Lavoifier finds, from his experiments, that the atmofpheric air is compounded of a pure and of a mephitic part. The first is only about one-fourth; the reft does not precipitate lime-water, but extinguishes candles, ftops refpiration, and does not form red vapours with nitrous air. In calcining mercury without addition, in clofe veffels, this pure part disappears, and

s again recovered by reviving it in the fame way; fo that the air, after the experiment, is exactly the fame as before. The air, which has been contaminated by the breathing of animals, is deprived of its pure part; and in its ftead, is tainted with about one-fixth of what is called fixed air: when this is absorbed by caustic alkali, the remainder is exactly the fame: with what appeared after the calcination of mercury. Refpiration therefore acts in two ways; and Mr. Lavoisier thinks it uncertain whether the lungs change the pure part of the air by any vapour which they emit, or abforb it, and again fupply the fixed air :- -We think the probability much in favour of the former opinion.

Combuftion feems chiefly to act on the pure part of the air, and to convert it into fixed air; for if the latter be abforbed by a cauftic alkali and pure air, in the fame quantity, added, the whole is reduced to its former state. The air, he thinks, is not fenfibly diminished; but different fubftances contaminate different proportions of the atmosphere. Candles destroy about one-tenth of the whole quantity, when they are extinguished; but even of the pure part, they deftroy only about two-fifths. Phofphorus will feparate four-fifths of it; and pyrophorus almoft the whole. Dephlogisticated air may, in this way, entirely be changed into fixed air; for, when the candle has been extinguished, if the fixed air is feparated by the alkali, the remainder will fupport the flame and if the air be quite pure, the experiment may probably be repeated, till the whole is confumed. Our author generally found a very small portion of the mephitic part of the atmosphere in it. This experiment, he thinks, ftrongly militates against Dr. Priestley's opinion, that flame is extinguished by phlogisticat ing the air.

:

Mr. Lavoisier next proceeds to those experiments, which in his opinion explain the nature and conftitution of acids. He de fcribes the appearances in burning Kunckel's phosphorus, and finds that the air is diminished nearly in the fame ratio in which the acid exceeds the weight of the original phosphorus. It is remarkable that the air is highly mephitic, and is reftored to its former ftate, by adding as much pure air as will compenfate for the decrease of bulk. The experiment fucceeds nearly in the fame way with fulphur; and the author concludes from hence, that both the vitriolic and phosphoric acids are compofed of dephlogisticated air, which forms above. half their weight. The reft of the effay contains the properties of the various falts which are formed from the union of the phosphoric acid with different bafes.

C.3

The

The next effay is very important. Its object is to prove not only that the air, but the most pure part of air, enters into the compofition of all the acids without exception; and that on this substance their acidity depends, infomuch that we may deprive them of that quality, or restore it again, by taking away or giving the portion of air effential to their compos fition.' Mr. Lavoifier allows that almost every experiment has been fuggefted by Dr. Priestley, and only contends for the honour of the conclufions. The principal experiment is to calcine mercury by means of the nitrous acid, and to revive it without addition. The metal loft in this trial but a small part of its weight, which arofe in the form of a yellow and red fublimate. Our author therefore concludes, that the air procured is entirely from the decompofition of the nitrous acid; confequently that this acid is compofed of 190 inches of nitrous air, 12 inches of common air, 224 inches of air better. than common air and water. It is well known that neither of these airs are really acid, though we have great reason to fufpect, that the nitrous air is virtually, though not formally, of this kind. But, though nitrous and dephlogisticated airs, to which these refults may be reduced, feem not to have any refemblance to an acid; yet, when united in a certain proportion, they form a true fmoaking spirit of nitre, Seven parts and one-third, of the former faturate four parts of the latter; yet the original proportion of pure air in the decompofition, was larger than of the nitrous.. This difficulty, Mr. Lavoifier profeffes himself unable to explain. The experiment fucceeds alfo with nitrous and common air; and it will be confequently obvious, if we truft thofe of our author, that air is not compofed of nitrous acid, but that the acid is compofed of air.

In the next effay, our author purfues a fimilar experiment with vitriolic acid and mercury; but does not recompound the acid. He is content with obferving, that the air abforbed by burning brimftone, is again decompofed; and that the vo latile vitriolic acid differs only from the fixed, by being deprived of a part of its dephlogisticated air.

The next object is, to explain the phænomena obfervable in burning pyrophorus. This fubftance, Mr. Lavoisier thinks, is a true liver of fulphur; and as it is formed from bodies containing vitriolic acid, and in its formation fuffers dephlo, gificated air to efcape, fo on its burning it returns to its for. er ftate, and recovers its air. The dephlogisticated air is fed in the experiment by the coaly matter, or what we call pik giften; and the inflammable air is different from that which is obtained from metals. It is always in proportion to

the