3 
on the Vapour of Acids. 29 
' 1 V , 
dephlogifticated air. The quantity of the liquor expended 
was about 2 oz. meafures. It may, however, be prefumed, 
that this fmall quantity of air came from fome of the acid 
which efcaped the aftion of the fire in the former procefs. In- 
deed its coming at the laft only may be confidered as a proof of 
this, as all the more volatile acid, which came over firft, 
yielded no air. 
I fubmitted a quantity of fpirit of fait to both thefe pro- 
cefles, viz. expofing it to a boiling heat in glafs tubes, her- 
metically fealed, and making the vapour pafs through a red 
hot earthen tube, but no air was produced in either cafe. In the 
former cafe, the water rufhed into, and completely filled, the 
tube, when it was opened under water; and in the other pro- 
cefs the liquor diftilled was precifely of the fame fpecific gra- 
vity, and, no doubt, in all other refpedts, the fame as before 
diftillation ; but the acid that remained in the retort was of 
lefs fpecific gravity, in confequence of the acid vapour being 
expelled by the heat in the form of marine acid air, which 
appeared not to be affedted by a red heat. 
Though, in the procefs with fpirit of fait, the refult be dif- 
ferent from that of thofe with oil of vitriol and fpirit of nitre, 
yet there is an analogy among all thefe three acids in this 
refpedt, viz. that the marine and both the volatile acids of 
vitriol and nitre are made by impregnating water with the 
acid vapour, fo that in its ufual ftate it may be faid to be phlo- 
gifticated as well as thefe. 
It was evident that the water in the worm-tub was much 
Xt> 
more heated by the diftillation of the fpirit of fait than by that 
of the oil of vitriol, and efpecially that of the fpirit of nitre ; fo 
that much of the heat by which it had been raifed in vapour 
muft, in the latter cafe, have been latent in the air that was 
Vql. LXXIX. U u formed ; 
