on thofe fubjects by tranfcribing his table; but we should add, that his determinations are as just as his premises are 18,16 The fecond fection is on the nature of acids, and the ge neral principles of the new theory. In this fection he adopts Mr. Lavoifier's fyftem of an oxygenous principle, though he differs from that author in its nature. He reitores too, on its native throne, the old principle of phlogifton. Indeed, in every inftance where the modern heretics fuppofe vital air to be concerned, Mr. Kirwan would fubftitute fixed air; though, if the existence of phlogiston be allowed, the difference is not of great confequence, fince vital air contami nated by it, in certain proportions becomes fixed air: and even in metallic calces, there is phlogifton enough to produce this change, which will appear when the air is feparated. There is little doubt of the existence of this principle in fome acids; but it is not equally evident in all. Mr. Lavoifier's table of the different affinities of the oxygenous principle is introduced; but is combated in almost every part: it is the object of Mr. Kirwan's criticism, and very defervedly, through the whole volume. On the vitriolic acid our author's obfervations are not very numerous, its acidifying ingredient is fuppofed to be fixed air; and, when volatile, he thaks it contains alfo fulphur. Though Mr. Kirwan feems to acknowlege that, in its formation, pure air is abforbed, he thinks it becomes fixed air, as a component part of the acid. Different arguments and experiments are adduced in fupport of this opinion; but they chiefly amount to this, that fixed air is feparated from it in different experiments. Our author is more explicit, and on a better foundation, when he shows that this acid becomes fulphur only on the addition of a pofitive principle. Mr. Kirwan's fection on the nitrous acid is a very valuable. one, and confiderably improves our knowlege of the nature of this very ufeful agent. Nitroas acid is compofed, in our author's opinion, of nitrous bafis, bis oxygenous principle, united to a small proportion of phlogifton: in other words, VOL. LXV, Jan. 1788: C of of fixed, pure, phlogifticated, and inflammable airs. Nitrous air, he supposes, confifts of the nitrous bafis, faturated with phlogiston; but it is not, in his opinion, a component part of the nitrous acid: that office is affigned to fixed air, and we regret that the length of our author's arguments, and the particular relation of his experiments, muft pievent our abridging or extracting them. Yet, as we have faid that the proportion of fixed air is sometimes too fmall to admit of its being confidered as a component part, we ought to infert our author's mode of obviating the objection. It may be faid with great appearance of truth, that the proportion of fixed air, thus obtained, is too fmall to deserve to be ranked among the conftituent parts of the nitrous acid. Before I answer this objection, it will be proper to determine in what proportion it fhould be contained in this acid; this proportion, as we have already feen, is variable, the phlogifticated acid containing leaft, and the dephlogisticated moft; but, in general, we may rate it at of the acid, as exifling in nitre. When the nitre is exposed to a red hear, the union of the conflituent parts of the acid is gradually broken; that part of the acid which is at the furface of the alkali, being in contact with the water, which is the most volatile ingredient, is not fo ftrongly acted upon by heat, but paffes undecompofed. The refiduary nitrous acid becoming now more and more concentrated, decomposes its own fixed air, and thereby becomes more and more phlogisticated. This phlogiftication continues to the lat, the retained part always dephlogifticating that which efcapes, until it is itself at laft forced out; and hence the laft portion is the most impure, and even contains nitrous air. That fixed air may be decompofed in this manner, appears from fundry other experiments; for inftance, that in which Dr. Priestley obtained dephlogisticated air from acetous felenite, 6 Pr. 292. and also, that in which both he and Mr. Laffone obtained air nearly of the goodness of common air, from limestone, after the greater part of the fixed air had paffed. 6 Pr. 227. "To make this matter ftill more intelligible, it must be observed, that if nitre be heated ever fo long, yet if we examine it at any period before its total decompofition, no part of the acid will be found phlogifticated, but that near the furface, which, in the inflant of its extrication, is dephlogiflicated, by the portion of the acid next under it, which then becomes phlogifticated, and is in the fame manner decompofed in its turn, by the next inferior ftratum; and this process continues until the whole is decompofed. This I have found, by pouring nitrous acid on melted nitre, which never expelled any more than a small portion of nitrous vapour; hence, Mr. Berthollet imagined that Mr. Bergman was deceived in afferting that phlogisticated nitre might be decompofed by the acetous acid; for, in effect, it can decompose but a fmall part of it, as only a fmall part of any portion of melted nitre is really phlogifticated; even dephlogifi *cated eated air from red precipitate, contains a portion of fixed air, as Dr. Priestley, Mr. Lavoisier, and Mr. Monge have obferved.' Mr. Kirwan next fhows, that the dephlogifticated air, fupposed to arife from nitre, cannot, as has been fufpected by Mr. Cavendish, and others, proceed from the decompofition of water; and he examines with great care the different refults from the decompofition of nitre by detonation with charcoal. He concludes, from the refult of this experiment by Lavoifier, and from the detonation of nitre with fulphur by Berthollet, that fixed air is actually formed by pure and inflammable air; that the phlogisticated air, of which nitrous acid pretty certainly con tains, is decompofed or deftroyed in the operation; and that nitrous air does not confift of nitrous acid, with the addition of phlogifton. He then examines pretty fully the famous experiment which first fuggefted the antiphlogiflic theory to M. Lavoisier; viz. the calcination of mercury, by means of the nitrous acid, and its revivification by heat: when, in the first inftance, it is feen copioufly to abforb pure air; and, in the fecond, to let it escape, while the different airs, into which the nitrous acid appears to be decompofed, make up, according to his calculation, the weight of the real acid employed. In this inftance it appears to be calcined by absorbing pure air, and to be revived by lofing it: no other power feems to be engaged in the operation. But this experiment Mr. Kirwan criticifes with his ufual accuracy, and fhows that the conclufion is drawn both haftily and unfairly; he afterwards gives the phlogistic explanation of this experiment. Mr. Kirwan then confiders the marine acid, in which he thinks fixed air is the oxygenous principle; and the dephlogifticated marine acid, in his opinion, is only the common acid with an increased quantity of fixed air. In this fect on his theory feems to fail; and we begin to find the clue which appears to have mifled him. It is perhaps improper, in any fenie, to fuppofe the oxygenous principle to be one, which is already an acid; for it may be at once asked, what gives to fixed air its acidity? The tortoife then is only put under the elephant. Our author, however, whofe ingenuity is confiderable, and whofe refources, from the extent of his chemical knowledge, are unbounded, finds great fupport for his opinion in different facts. But it cannot escape an attentive reader of his work, that his arguments are most striking where the acid contains phlogiston, in any quantity, and lefs fo where that quantity is inconfiderable. He is of courfe led to fufpect that the fixed air, which is the refult of the decompofition, is either that portion which is abforbed from the atmosphere, or produced by an accidental. contamination. In a former Review, we gave an account of M. Berthollet's very accurate and inftructive experiments on C 2 tha of fixed, pure, phlogifticated, and inflammable airs. Nitrous air, he fuppofes, confifts of the nitrous bafis, faturated with phlogiston; but it is not, in his opinion, a component part of the nitrous acid: that office is affigned to fixed air, and we regret that the length of our author's arguments, and the particular relation of his experiments, muft prevent our abridging or extracting them. Yet, as we have faid that the proportion of fixed air is fometimes too fmall to admit of its being confidered as a component part, we ought to infert our author's mode of obviating the objection. • It may be faid with great appearance of truth, that the proportion of fixed air, thus obtained, is too fmall to deferve to be ranked among the conftituent parts of the nitrous acid. Before I answer this objection, it will be proper to determine in what proportion it fhould be contained in this acid; this proportion, as we have already feen, is variable, the phlogifticated acid containing leaft, and the dephlogifticated moft; but, in general, we may rate it at of the acid, as exifting in nitre. When the nitre is exposed to a red heat, the union of the conftituent parts of the acid is gradually broken; that part of the acid which is at the furface of the alkali, being in contact with the water, which is the most volatile ingredient, is not fo ftrongly acted upon by heat, but paffes undecompofed. The refiduary nitrous acid becoming now more and more concentrated, decomposes its own fixed air, and thereby becomes more and more phlogisticated. This phlogiftication continues to the laft, the retained part always dephlogifticating that which efcapes, until it is itself at laft forced out; and hence the laft portion is the most impure, and even contains nitrous air. That fixed air may be decompofed in this manner, appears from fundry other experiments; for inftance, that in which Dr. Priestley obtained dephlogisticated air from acetous felenite, 6 Pr. 292. and also, that in which both he and Mr. Laffone obtained air nearly of the goodness of common air, from limestone, after the greater part of the fixed air had pafied. 6 Pr. 227. "To make this matter ftill more intelligible, it must be obferved, that if nitre be heated ever fo long, yet if we examine it at any period before its total decompofition, no part of the acid will be found phlogificated, but that near the furface, which, in the inftant of its extrication, is dephlogifticated, by the portion of the acid next under it, which then becomes phlogisticated, and is in the fame manner decompofed in its turn, by the next inferior ftratum; and this process continues until the whole is decompofed. This I have found, by pouring nitrous acid on melted nitre, which never expelled any more than a small portion of nitrous vapour; hence, Mr. Berthollet imagined that Mr. Bergman was deceived in afferting that phlogifticated nitre might be decompofed by the acetous acid; for, in effect, it can decompofe but a fmall part of it, as only a fmall part of any portion of melted nitre is really phlogifticated; even dephlogifi cated eated air from red precipitate, contains a portion of fixed air, as Dr. Priestley, Mr. Lavoisier, and Mr. Monge have observed.' Mr. Kirwan next fhows, that the dephlogifticated air, fuppofed to arife from nitre, cannot, as has been fufpected by Mr. Cavendish, and others, proceed from the decompofition of water; and he examines with great care the different refults from the decompofition of nitre by detonation with charcoal. He concludes, fromthe refult of this experiment by Lavoifier, and from the detonation of nitre with fulphur by Berthollet, that fixed air is actually formed by pure and inflammable air; that the phlogisticated air, of which nitrous acid pretty certainly contains, is decompofed or deftroyed in the operation; and that nitrous air does not confift of nitrous acid, with the addition of phlogifton. He then examines pretty fully the famous experiment which first fuggefted the antiphlogiftic theory to M. Lavoisier; viz. the calcination of mercury, by means of the nitrous acid, and its revivification by heat: when, in the firft inftance, it is feen copioufly to abforb pure air; and, in the fecond, to let it escape, while the different airs, into which the nitrous acid appears to be decompofed, make up, according to his calculation, the weight of the real acid employed. In this inftance it appears to be calcined by absorbing pure air, and to be revived by lofing it: no other power feems to be engaged. in the operation. But this experiment Mr. Kirwan criticifes with his ufual accuracy, and fhows that the conclufion is drawn both haftily and unfairly; he afterwards gives the phlogiftic explanation of this experiment. Mr. Kirwan then confiders the marine acid, in which he thinks fixed air is the oxygenous principle; and the dephlogifticated marine acid, in his opinion, is only the common acid with an increased quantity of fixed air. In this fection his theory feems to fail; and we begin to find the clue which appears to have mifled him. It is perhaps improper, in any fenfe, to fuppofe the oxygenous principle to be one, which is already an acid ; for it may be at once afked, what gives to fixed air its aci. dity? The tortoife then is only put under the elephant. Our author, however, whofe ingenuity is confiderable, and whose refources, from the extent of his chemical knowledge, are unbounded, finds great fupport for his opinion in different facts. But it cannot escape an attentive reader of his work, that his arguments are inoft ftriking where the acid contains phlogiston, in any quantity, and lefs fo where that quantity is inconfiderable. He is of courfe led to fufpect that the fixed air, which is the result of the decompofition, is either that portion which is abforbed from the atmosphere, or produced by an accidental contamination. In a former Review, we gave an account of M. Berthollet's very accurate and inftructive experiments on |