292, Dr. Priestley’s Experiments 
before diftillation, it will appear, that there muft have been 
a great lots of acid vapour, which was either retained in the 
water of the trough, or efcaned through it. 
I do not fee that thefe experiments can be explained, but on 
the fuppofition that the moft dephlogifticated oil of vitriol and 
fpirit of nitre are, in a proper fenle, faturated with phlogifton ; 
and that when part of the acidifying principle is expelled in 
the form of the air, the remainder is fuperfatu rated with it. 
To try whether the acid, thus fuperfaturated with phlo- 
gifton, was convertible into pure air by this procefs, I heated 
the liquor collected after the diftiilation of the oil of vitriol, 
that is, water impregnated with vitriolic acid air, and made 
the vapour pafs through the hot tube, but no air came from 
it ; and when collected a fecond time, it was not at all different 
from what it had been before. The fpecific gravity was alfo 
the fame. 
It is evident, however, though this procefs does not fhew it, 
that the volatile vitriolic acid contains the proper element of 
dephlogifticated air; fince by melting iron in vitriolic acid air, 
a quantity of fixed air (which is compoled of inflammable and 
dephlogifticated air) is produced. Melting iron in 9 oz. mea- 
fures of vitriolic acid air, it was reduced to 0.3 oz. meafures, 
and of this o. 1 7 oz. meafures was fixed air. I repeated the 
experiment with the fame refult, and putting the refiduums 
together found the air to be inflammable. 
But the refult was fomething different when I fent through 
the hot tube the liquor that I had collected in the procefs with 
fpirit of nitre. No air, however, was produced at the firft, 
nothing appearing befides a red vapour that was wholely abforbed 
by water, or efcaped through it into the atmofphere ; but 
.towards the end of the procefs I collected 10 oz. meafures of 
dephlo- 
