Mr, Kinwan’s Remarks, &e. 450 
tion of nitrous by mixture with refpirable air, the, phiogiftica- 
tion of refpirable air by the electric fpark, and, laftly, that ef- 
fected by amalgamation. In each of thefe inftances Mr, Caven- 
DIsH is of opinion, that the diminution of refpirable air is 
owing to the production ef water, which, according to him, is 
formed by the union of the phlogifton, difengaged in thofe pro- 
cefles, with the dephlogitticated part of common air; and that 
fixed air is never produced in phlogiftic procefies, except fome 
animal or vegetable {ubftance is concerned in the operation, 
from whofe decompofition it may arife. ‘To which of thefe 
caufes the diminution of refpirable air is to be attributed, I thall 
now endeavour to elucidate. 
Of the Calcination of Metals. 
I attributed the diminution of air by the calcination of 
metals, to the converfion of the dephlogifticated part of com- 
mon air into fixed air, by reafon of its union with the phlo- 
gifton of the metal, for this plain reafon, becaufe I find it ac- 
knowledged on all hands, that the calces of all the bafe metals 
yield fixed air, when fufficiently heated. Mr. Cavendith allows 
the fact in general, but afcribes the fixed air found in them to 
their long expofure to the atmofphere, in which he fays fixed 
air pre-exifts ; but that it exifts in common air in any quantity 
worth attending to, or is extracted from it in any degree, I 
take the liberty of denying, grounded on the following facts. 
Firft, I have frequently agitated 18 cubic inches of common air 
in 2 of lime-water, and 2 of common air in 18 of lime-water, 
but could never perceive the flighteft milkinefs; and yet the 
thoufandth part of a cubic inch of fixed air would thus be made 
fenfible ; for if a cubic inch of it be diffolved in 3 ounces of 
. xX 2 water, 
