which he placed fome fishes, killed them in lefs than a mi

nute's time.

Sect. XIV. muft to thofe who are in the leaft verfed in aerial experiments contain information of the moft intereft. ing nature; it teaches us how to procure dephlogisticated air with very little toil and expence. For this purpofe nothing more is neceffary than an earthen retort and a reverberatory furnace;' (for which, however, one black pot or Hefiian crucible inverted over another anfwers very well.) Every ounce of nitre, by the help of this apparatus, will yield a hundred ounces of very pure air, and the fire may be fo regulated, that the production of air fhall be more equable, and the proćefs more manageable than in any other method hitherto employed.' The Doctor fuppofes, that those who cannot furnifh themselves with a reverberatory, may fucceed very well in the fame procefs, by covering the retort with coals in a common fire. This method is that in which the Doctor first procured pure air, without knowing what he had gotten. Mr. Scheele, however, is the person to whom we must give the credit of reducing it to practice. One ounce of alum, by this method of operating, may be made to yield fixty ounces at leaft of pure, mixed with a fmall portion of fixed air.This experiment, as well as a variety of other facts, in which the vitriolic acid alone is concerned in the production of pure air, led the Doctor to correct his theory of the conftituent principles of air: he had formerly fuppofed thefe to be an earth, the nitrous acid and a quantity of phlogifton; but he now wifhes not to fpecify the particular acid; but more generally to fay, that fome acid principle is neceffary to the conftitution of air: his reafonings on this fubject, he obferves, lead us to a method of obtaining a truly primitive earth, or an earthy principle' common to all earths aud metallic calces whatfoever.

In the course of this fection it appears that all that mercury wants to make it capable of yielding pure air, is the lofs of its phlogifton, and the acquifition of fome acid principle. But fince (according to Dr. Crawford's theory, which Dr. Priestley does not pretend to have properly confidered) air, in parting with its phlogifton, acquires the principle of heat, are not thefe two things the fame, heat and pure acid, which is nearly the idea of Mr. Scheele ?-But as this principle of heat does not, in any other cafe, appear to affume the form of air, and has not been found to have weight, which all acids, and dephlogifticated air alfo, have; it feems to be more probable, that the calx in parting with this phlo

gifton,

giston, takes from the air two diftinct principles at the fame time, viz. That of heat, (if Dr. Crawford's theory be true,) and this acid.'—We think Dr. Priestley has, in this paffage, bestowed much fruitlefs pains upon two most abfurd and extravagant fyftems; his objection to Scheele's theory is indeed decifive, but it is one only of a multitude which might be produced to the fame effect. He wifely expreffes his doubts about Dr. Crawford's fyftem; but probably he feels himself no longer a fceptic. The filence with which Dr. Crawford has regarded a most reputable adversary, who has charged him in the most pointed manner, of blunders, and of abfurdities, is to us an evidence more than prefumptive, either that he has nothing to say in defence of himself, or a great deal to unfay concerning his theory. We have expected fome answer for a long time, and we hope our expectations will not at laft be disappointed. This fection concludes with a decifive fact, proving that mercury calcines much more eafily in dephlogif ticated than in common air. The Doctor intimates that, by an attention to this fact, the precipitate per fe may be made with much lefs time and expence than it now is.'

6

Several of Dr. Prieftley's friends had expreffed fome little doubt to him, of the accuracy of nitrous air, as a teft of the purity of other airs. This fcepticifm, relating to one of his most important difcoveries, has called forth a great part of the fifteenth fection: Dr. Priestley really finds that an animal will live much longer in dephlogisticated air, than the' nitrous teft of its purity would lead him to expect. The air in which a moufe lived three hours, and which, when the mouse was taken out, was found to be very little phlogisticated, by the nitrous teft was difcovered to be only four times purer than the common air in which a moufe would have lived half an hour only. This ftriking difference between the two tefts Dr. Prieftly afcribes to the confinement of the animal, which prevented it from phlogisticating the air fo faft as it would have done in cafe it had been more vigorous. This is conjecture only, and, we think, to give it as fuch the leaft weight, the Doctor has first of all a great deal to do; he should certainly have afforded us some reason to believe from experiment, that animals in a weak ftate do really phlogifticate air less than when in full ftrength. An enquiry which would inform and convince us in this particular, would, independent of its connexions with the difficulty advanced in this fection, be fo interefting and curious, that we much regret the Doctor's inattention to it. The offenfivencfs of breath, which is the ufual attendant of the human conftitution in its laft ftate of weaknefs, if it depend on the phlogiston of the refpired air,

ought moft certainly to be attended to in this cafe. Befides, if, as may be fairly concluded from fome other parts of his works, it be the Doctor's opinion that the nutrition of the human frame is in proportion to the phlogiston it imbibes from the food employed for its nourishment, how are we to reconcile this with the idea, that the moft healthy and vigorous conftitutions discharge the greateft quantity of fuperabundant phlogifton; or that their blood is leaft able to retain that principle which conftitutes the nutritious quality of our aliment? It cannot be alledged here, that this is owing to the greater quantity of aliment which they take; for we very well know, that fome of the moft healthy, vigorous, and fucculent perfons, are those who have very small appetites. In our opinion, the difficulty of reconciling the two tests still operates with full force; and we are much furprised that the Doctor, who is generally fo copious on moft fubjects, should be contented with one experiment only, in a cafe which combats his most useful, if not his most brilliant discovery.—The remainder of this fection is employed in correcting a most egregious blunder committed by Dr. Ingenhoufz. This is an office which we find him discharging more than once in the course of this volume; and we are apt to think, from our own experience, that if the delicacy of friendship had not reftrained him, he might have informed the public of many other errors in that gentleman's work, which are too glaring to be overlooked by the most common experimentalist; in the prefent inftance, however, it is fhewn, that Dr. Ingenhoufz is wrong, in what the Doctor flattered himself was a most important difcovery, viz. that of making dephlogisticated air ferve thirty times longer than when it is used in the common way. It is evident, at firit fight, that Dr. Ingenhoufz falls here into Meffrs. Kirwan and Cruickshank's error, viz. that phlogistication changes common into fixed air; and that by paffing air after it is breathed through lime-water, you deprive it of its noxious ingredients.-The Doctor is not contented with the decifive facts he has enumerated in other cafes, in oppofition to this opinion, but he makes an experiment, in which two mice are thrown into convulfions by the frequent refpiration of pure air, notwithstanding the precautions prefcribed by Dr. Ingenhoufz.

Sec. XVI. contains fome obfervations on fixed air.Sect. XVII. treats of the state of air in water, by which it appears, that the air you expel from water in géneral contains a portion of fixed air; that the air you get from limewater is much purer than common air; and that the air you expel from water in which vegetables have grown, is dephlo

gifti

1

2:

gifticated.-Sect. XVIII. prefents us with a variety of obfervations on the nature of fixed air. 1. From fome facts récited by Dr. Priestley we are left in fome doubt, whether or not there be any water in the conftitution of nitrous air. He finds no difference in the ftrength of nitrous air procured by a flow produce, and that which was produced with great rapidity. 3. Dr. Priestley points out the changes in nitrous air, when produced from iron. 4. He defcribes the changes in the colour of liquids by which air is confined. 5. The Doctor proves that nitrous air is not changed by exposure to water in a fand-heat. 6. He treats of a fingular change produced in nitrous air, after being long kept in water.-Sect. XX. is employed in refuting another blunder of which the Abbé Fontana is the author, and Dr. Ingenhoufz the publishDr. Priestley begins this section with fhewing the striking diminution produced in a quantity of nitrous air, merely by throwing it up into a long tube filled with water. Hence, he obferves, how important it is in measuring the purity of air by this teft, to bring the two airs into contact through as fhort a paffage of water as poffible.

er.

Dr. Ingenhoufz, in his book, fays that the Abbé Fontana had discovered a method of employing nitrous air as a test, in the use of which the strength of the nitrous air was of little or no confequence; inftead of throwing equal measures of nitrous and common air into the eudiometer, he would throw feveral measures of nitrous air, fo that however weak, the abundance of the air used agreeably to this mode might fupply phlogifton enough to the common air, and at the end of the operation, the diminution would be just the fame, as if one measure only were used. In this inftance Dr. Ingenhoufz and the Abbé Fontana muft have proceeded folely from conjecture; they could never have examined the accuracy of this mode by experiment, or they must have obferved the difference which Dr. Priestley discovered, This, however, is not the only cafe in which we have lately detected philofophers, in the recommendation of inftruments and other modes of operation, of the use, or the accuracy of which they could have no other evidence than fuch as their own speculative and unexperienced imaginations afforded them. With respect to eudiometers, machines for determining the conducting powers of heated bodies, we could produce feveral instances in which it was abfolutely impoffible for the authors either to try or to conftruct what they propofed: they would otherwise have difcovered how much they infulted the credulity of others, and exposed their own prefumption and ignorance. Dr. Priestley is not contented with facts alone, on the prefent occafion, but pro

N 3

produces fome ftriking arguments to complete the refutation of this error; and we are not a little furprised to find him praife, at the conclufion of this fection, as a difplay of ingenuity, what he has previously expofed, as contrary to fact and the most obvious arguments.

We are very forry that the limits within which we are neceffarily confined will not allow us to follow the author through thofe curious fections in which he treats of dephlogisticated nitrous air, or that species of nitrous air in which a candle will burn with an enlarged flame. We pass on to the twenty-fecond section, which prefents us with a most wonderful and unaccountable phænomenon: in his fecond volume Dr. Priestley informed us, that a portion of alkaline air, in confequence of paffing the electric fhock or fpark through it, would be confiderably increased; that the additional air produced by this operation was inflammable; and that, in confequence of the admiffion of water to the increased portion of air, all that was alkaline would be abforbed. In this volume Dr. Priestley fuppofes that he found the limit of the increase; and that the whole air, after the procefs, was nearly as poffible three times as much as that which the alkaline air alone had occupied.

From the authority of a very accurate correfpondent, we muft beg leave to inform the Doctor, that he is certainly mif taken in this particular..--For, 1. By difcharging two hundred explosions of a two-gallon jar through half a cubic inch of this air, it was actually increafed to above feven times its bulk. 2. A great variety was found in confequence of fending the explosion through different specimens of this air. 3. By the admiffion of water into the tube employed in the experiment; all, or by far the greateft part of the alkaline air, was abforbed. From this ftrange fact, we feel a hoft of doubts arifing in moft formidable array in our minds against the Doctor's whole theory of the conflitution of atmospheric air. 1. Where is the constituent earth in this experiment neceffary for the production of fo much air? 2. Where the

acid? It cannot be urged that these are derived from the alkaJine air; that continues apparently unaltered, for on being mixed with water, the water difcovers all the properties which it poffeffes when impregnated with alkaline air, without undergoing the process in this experiment. We might have afked farther, whence comes the phlogiston alfo? But Mr. Bewly answers, in the Appendix, that it probably comes from the alkali, which abounds with it; and that the electric fluid may poffibly add to the quantity of inflammable air contained in the alkaline air, by carrying phlogifton with it from the

bodies