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XI. Experiments and Obfervations relating to the "Principle of 
Acidity, the Compofition of Water , and Phlogijlon . By 
Jofeph Prieftley, LL.D. F. R. S. 
Read February 7, 1788. 
T HAT water confifts of two kinds of air, dephlogifti- 
cated and inflammable, is now, I believe, generally 
admitted as one of the moft important, and beft afcertained, 
dodhines in chemiftry. My own experiments having feemed 
to favour it, I made no difficulty of receiving it myfelf : but 
having, at the time of the publication of the laft Volume of 
my Experiments, found that, in decompofing the two kinds 
of air above mentioned by the eledtric fpark, I got much lefs 
water than I expedted, and, inftead of it, a dark-coloured va- 
pour, not eafily condenfed, I could not help concluding that 
fomething yet remained to be invefliigated with refpect to this 
fubjedt, and determined, at a proper opportunity, to refume 
my inquiries into it. 
At that time, however, I had no fufpicion of any acid 
being produced in the procefs ; having never been able to find 
any in the water which I had hitherto procured in pretty large 
quantities from the decompofition of thofe two kinds of air, 
though the dodtrine of dephlogifticated air being, or contain- 
ing, the principle of univerjal acidity , had been advanced by 
M. Lavoisier, and admitted by myfelf and others. 
Sufpedting that much of the water which had been procured 
U 2 in 
