P hloglfticatlon of Spirit of Nitre . 1 4 ^ 
the tube; and Tome objedtion will always remain to the expe- 
riment from the impurity of the air made ufe of. 
Having repeatedly obferved, that the acid became coloured 
in eonfequence of beiir.g expofed to heat in contadl with any 
kind of air whatever, I expofed at the fame time, and in the 
fame circumltances, three equal quantities of the fame colour- 
lefs fpirit of nitre, in three nearly equal tubes, one containing' 
dephlogifticated, another phlogifticated, and a third inflamma- 
ble air; that, if there fhould be any difference in the colouring 
of the acid in thefe cafes, it might be- the more eafily per- 
ceived. But though I gave all the attention that I could, I did 
not perceive that there was any difference, except what arofe 
from fome of the tubes being placed a little nearer the fire 
than the reft ; and, by changing their places, the colour was 
at length the very fame in them all. 
As in thefe three cafes I examined the air before and after 
the procefs, in the manner above mentioned, I fhall juft recite 
the particulars. 
Of the dephlogifticated air the tube contained before the pro- 
cefs 1.46 oz. m. of the ftandard of 0.67, and after the procefs 
it contained 1*76 oz. m. of the ftandard of 0.77 ; a difference 
owing in part to the mixture of common air, which could note 
be excluded in the fealing of the tube, and in part to the air 
emitted from the acid not being pure. 
Of the phlogifticated air, the tube contained 1.3 oz,. m*. 
and after the procefs 1.95 oz. m. of the ftandard of 1.38. 
Of the inflammable air,., the tube contained before the pro- 
cefs 1.52 oz. m. and after the procefs 1.9 oz. m. of the ftan-- 
dard of 1.8. They were all meafured by a mixture of two 
equal quantities of nitrous air. 
If 
