162 - on Mr. Kirwan’s Remarks on. Mi 
when 1 made the experiment’ with nitrous air prepared and 
confined by the water of my tub, I found lime-water admitted 
to it inftantly precipitated. “But after I-had read Mr. Caven= 
DisH’s paper, which he had the politenefs to permit, me, and 
had, according to his direGtion, received the nitrous air over. 
lime-water, I did not then perceive the leaft milkinefs after ad- 
mitting common air. After 12 hours ¥ indeed. perceived a 
whitith’duft, on the bottom of the glafs veflél im which I made 
the experiment, which I cannot aflure to be ‘calcareous; and, 
on breathing into the lime-water, an evident milkinefs enftied; 
fo that I little doubt but the precipitation I obferved in the firft 
experiment arofe from the decompofition of the aerial felenite 
contained in the water of the tub. And itis very poflible that 
the precipitation of lime, which I perceived fome years agoon 
mixing dephlogifticated air and nitrous air, might have arifen 
from the fame caufe, or from fixed ‘air pre-contained in the de- 
phlogifticated, as this laft had not been wathed in lime-water. 
YetI do not think the failure of this experiment at all conclufive 
againft the fuppofed production of fixed air on this occafion, 
becaufe the quantity of fixed air is fo fmall, that it may well be 
fuppofed to unite to the nitrous felenite formed in the lime- 
water. It is well known that a fmall quantity of fixed -air is 
capable of uniting to all neutral falts: thus Dr. PrizsTLEy has 
extracted it from) tartar vitrialate and alum, (2 PR. 1 Fis I 16.) 
and gypfum, (2 Pr. 80.); and Dr. Mac Brive found it in, nitre 
and common falt, though in {mall quantity. But to try whether 
nitrous felenite would attract any, I made a folution of chalkin 
nitrous acid, which, when faturate, weighed 381,25 grains ; but, 
being expofed to 'the air fora few hours, it weighed 382,25. I 
afterwards took avery dilute nitrous acid, in whichan acid tafte 
was barely perceptible, and impregnated it with a very {niall pro- 
ME 7 portion 
