324 Dr. Priestley’s Experiments and Obfervations on 
cipally to know, namely, the quantity and the kind of the 
contained acid. 
The quantity of the green liquor was 442 grains, and its 
fpecific gravity was to that of water as 1022 to 1000. When 
the green liquor was poured out of the phial, there remained 
at the bottom 72 grains of a brown powder, which upon exa- 
mination was found to be a calx of copper, foluble in acids,' 
but not in water. 
The colour of the liquor {hewed that it was a folution of 
copper. However, it gave no cupreous precipitation topolifhed 
fteel, till a few drops of acid had been added. This circum- 
ftance feemed to {hew the perfect faturation of the acid of the 
green liquor with the copper ; and this complete faturation was 
further evinced by the very fmall alteration of colour which 
litmus buffered on being mixed with this liquor. This teft did 
indeed feem to acquire a little tendency to rednefs, but the 
effect was fo minute as not to deferve confideration, and might 
probably be owing to fome flight phlogiffication, as it is called, 
of the acid contained, rather than to its fuperabundance. 
Upon evaporating the green liquor by expofure to air, with- 
out the application of heat, no cryltals were formed, but a 
dry green powder, infoluble in water, but foluble in acids. 
You had before acquainted me with this faff. As folutions of 
copper in the nitrous acid are known to yield deliquefeent cry-^ 
lfals, and as no cryftallization happened in this inftance, al- 
though the acid was evidently nitrous, I was defirous of difeo- 
vering the caufe of this difference between this liquor and com- 
mon folutions of copper in the nitrous acid. Upon making 
fome trials with this view, 1 found that there were three periods 
or ftages to be diflinguifhed in the combination of copper with 
the nitrous acid. The firft period is when the acid is fuper- 
2 abundant, 
