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Experiment VI. 
Thinking that the difference in the bulks of the 
water before and after folution might be owing to the 
feparation and efcape of fome volatile principle ; 
I took care to balance as accurately as I could, water 
and fal gemmae, water and fait of tartar, water and 
vitriolated tartar, &c. and then putting the feveral 
falts into the water, I obferved when the folution 
was accompl idled, whether the equilibrium of the 
fcales was affeded, but I could not diftinguifh any 
change. Dr. Hales and others have fpoken of the 
exiftence of air in falts, and have in two or three 
inftances inveftigated the quantity, but after a very 
different manner from that I have ufed ; nor can I 
think myfelf at liberty to efteem this air which is 
feparated by folution, of the fame nature with that 
which is called by him and others fixed air, inafmuch 
as fixed air makes a confiderable part of the weight 
of the bodies from which it is extraded, precipitates 
lime water, and is feldom difcharged (or perhaps pro- 
duced from fome of the minute parts of the body 
being converted by the violence of the fire, &c. into 
an elaftic fluid), except when the body is decom- 
pofed ; whereas this makes only a confiderable part 
of the bulk of bodies, and thus diminifhes their 
fpecific gravity without fenfibly increafing their ab- 
folute weight; does not, as I colleded from fome 
rough trials, render lime water turbid ; and is fet at 
liberty, though not by a mechanical divifion, yet by 
an operation fomewhat different from chemical be- 
comjjofition. It hath been remarked by fome, that 
fal in e 
