lines as being (as Dr. Cullen obferves) in the mildest ftate, and therefore moft likely to generate moft air.

I fhook the phial often, and threw many ftreams of air on the blood, as I have often practifed with success for impregnating water; but could not perceive the fmalleft figns of coagulation, although it stood in an atmosphere of fixed air 20 minutes or more. I then uncorked the bottles, and poured off about ii to which I added about 6 or 7 gtts of spirit of vitriol, which coagulated it immediately. I fet the remainder in a cold place, and it coagulated, as near as I could judge, in the fame time that blood would have done newly drawn from the vein.

P. 82. Perhaps the circumftance of putrid vegetables yielding all fixed and no inflammable air, may be the causes of their proving fo antifeptic, even when putrid, as appears by Mr. Alexander's experiments.

P. 86. Perhaps the putrid air continually exhaled may be one cause of the luxuriancy of plants growing on dunghills or in very rich foils.

P. 146. Your observation that inflammable air confifts of the union of fome acid vapour with phlogiston, puts me in mind of an old obfervation of Dr. Cullen, that the oil feparated from foap by an acid was much more inflammable than before, refembling effential oil, and foluble in V. fp.

I have tried fixed air as an antifeptic taken in by refpiration, but with no great fuccefs. In one case it feemed to be of fervice, in two it seemed indifferent, and in one was injurious, by exciting a cough.

NUM

Extract of a Letter from Mr. WILLIAM BEWLEY, of GREAT MASSINGHAM, NORFOlk.

Dear Sir,

March 23, 1774.

When I first received your paper, I happened to have a procefs going on for the preparation of nitrous ether, without distillation *. I had heretofore always taken for granted that the elaftic fluid generated in that preparation was fixed air: but on examination I found this combination of the nitrous acid with inflammable fpirits, produced an elastic fluid that had the same general properties with the air that you unwillingly, though very properly, in my opinion, term nitrous; as I believe it is not to be procured without employing the nitrous acid, either in a fimple state, or compounded, as in aqua regia. I fhall fuggeft, however, by and by, fome doubts with respect to its title to the appellation of air,

Water impregnated with your nitrous air certainly, as you fufpected from its tafte, contains the nitrous

*The first account of this curious procefs was, I believe, given in the Mem. de l'Ac. de Sc. de Paris for 1742. Though feemingly lefs volatile than the vitriclic ether, it boils with a much smaller degree of heat. One day laft fummer, it boiled in the cocleft room of my house; as it gave me notice by the explosion attending its driving out the cork. To fave the bottle, and to prevent the total lofs of the liquor by evaporation, I found myself obliged instantly to carry it down to my cellar.

acid. On faturating a quantity of this water with a fixed alkali, and then evaporating, &c. I have procured two chryftals of nitre. But the principal obfervations that have occurred to me on the subject of nitrous air are the following. My experiments have been few, and made by fnatches, under every difadvantage as to apparatus, &c. and with frequent interruptions; and yet I think they are to be depended upon.

My first remark is, that nitrous air does not give. water a fenfibly acid impregnation, unless it comes into contact, or is mixed with a portion of common or atmospherical air and my second, that nitrous air principally confifts of the nitrous acid itself, reduced to the state of a permanent vapour not condenfable by cold, like other vapours, but which requires the prefence and admixture of common air to restore it to its primitive state of a liquid. I am beholden for this idea, you will perceive, to your own very curious difcovery of the true nature of Mr. Cavendish's marine

vapour.

When I first repeated your experiment of impregnating water with nitrous air, the water, I muft own, tafted acid; as it did in one, or perhaps two trials afterwards; but, to my great aftonishment, in all the following experiments, though fome part of the factitious air, or vapour, was vifibly abforbed by the water, I could not perceive the latter to have acquired any fenfible acidity: I at length found, however, that I could render this fame water very acid, by means only of the nitrous air already included in the phial with it. Taking the inverted phial out of the water, I remove my finger from the mouth of it, to admit a

little of the common air, and instantly replace my finger. The redness, effervefcence, and diminution take place. Again taking off my finger, and instantly replacing it, more common air rushes in, and the fame phenomena recur. The process fometimes requires to be seven or eight times repeated, before the whole of the nitrous vapour (as I shall venture to call it) is condensed into nitrous acid, by the fucceffive entrance of fresh parcels of common air after each effervefcence; and the water becomes evidently more and more acid after every such fresh admiffion of the external air, which at length ceases to enter, when the whole of the vapour has been condenfed. No agitation of the water is requifite, except a gentle motion, just fufficient to rince the fides of the phial, in order to wash off the condenfed vapour.

The acidity which you (and I likewise, at first) obferved in the water agitated with nitrous air alone, I account for thus. On bringing the phial to the mouth, the common air meeting with the nitrous vapour in the neck of the phial, condenses it, and impregnates the water with the acid, in the very act of receiving it upon the tongue. On ftopping the mouth of the phial with my tongue for a fhort time, and afterwards withdrawing it a very little, to suffer the common air to rush paft it into the phial, the fenfation of acidity has been fometimes intolerable taking a large gulph of the water at the fame time, it has been found very flightly acid.---The following is one of the methods by which I have given water a very ftrong acid impregnation, by means of a mixture of nitrous and common air.

but

Into a small phial, containing only common air, I force a quantity of nitrous air at random, out of a bladder, and inftantly clap my finger on the mouth of the bottle. I then immerse the neck of it into water, a fmall quantity of which I fuffer to enter, which fquirts into it with violence; and immediately replacing my finger, remove the phial. The water contained in it is already very acid, and it becomes more and more fo (if a fufficient quantity of nitrous air was at first thrown in) on alternately ftopping the mouth of the phial, and opening it, as often as fresh air will enter.

Since I wrote the above, I have frequently converted a small portion of water in an ounce phial into a weak aqua fortis, by repeated mixtures of common and nitrous air; throwing in alternately the one or the other, according to the circumstances; that is, as long as there, was a fuperabundance of nitrous air, fuffering the common air to enter and condense it: and, when that was effected, forcing in more nitrous air from the bladder, to the common air which now predominated in the phial---and so alternately. I have wanted leifure, and conveniencies, to carry on this procefs to its maximum, or to execute it in a different and better manner; but from what I have done, I think we may conclude that nitrous air confifts principally of the nitrous acid, phlogisticated, or otherwife fo modified, by a previous commenstruation with metals, inflammable fpirits, &c. as to be reduced into a durable elastic vapour : and that, in order to deprive it of its clafticity, and reftore it to its former ftate, an addition of common air is requifite, and, as I fufpect, of water likewife, or fome other fluid as in the courfe