Acidity , the Compojition of Water , and Phlogifon, 1 51 
By the afliitance of Mr. Keir I examined thefe folutions of 
copper, and prefently found, by means of a folution of terra 
ponderofa in fpiritof fait, that it was not, in any of the cafes, 
the vitriolic ; and yet, as the dry fubiLance left by the evapo- 
ration of the liquor did not deliquefce, I had concluded, that 
the acid was neither the nitrous, nor the marine ; but Mr. 
Keir informs me, that this is the cafe with a fully fatu rated 
folution of copper in fpirit of nitre. 
Alfo Dr. Withering, who was fo obliging as to examine 
fome of thefe liquors for me (for, not being much accuilomed 
to thefe analyfes, I had requeiled him to undertake it) had pro- 
cured from that in the production of which the red lead had 
been ufed, cryilals of nitre, and other indifputable indications 
of nitrous acid ; fo that I was fatisf ed that it was this acid that 
was produced in all the cafes. 
I had a farther proof of the acid being the nitrous, that 
having (in order to get a quantity of liquor that fhould be as 
little faturated with any metal as poiiible) ufedaveilel of tinned 
iron , I found, that after fome time, when the tin had been 
much corroded (and with every procefs a confiderable quan- 
tity came away) the liquor, which at firil was colourlefs, was 
tinged with red. In theie experiments I made ufe of dephlo- 
giilicated air from red lead. 
As both the kinds of air made ufe of in thefe experiments 
were exceedingly pure, it feems evident, that phlogiilicated 
air does not contain all the elements of nitrous acid ; but only 
fupplies a bafe for it, the dephlogiilicatsd air (which was ufed 
in a greater proportion in the valuable experiment of Mr. Ca- 
vendish) fupplying the acidifying principle, as I had con- 
jectured in the lail Volume of my § x P er iments, p'. 404. Be- 
sides, though all phlogiilicated air could not be excluded in thofe 
2 experi- 
