2:8 Continuation of the Experiments and' Gbferv'ations 
If the above experiments be attended to, the anfwer to the 
fecond queftion will be equally obvious. It is certain, that 
common air does not- confift of one- fourth of its bulk of fixed 
air ; for if it did, the remaining three- fourths mud be dephlo- 
gifticated air : and if fo, then the abfolute weight of a mix- 
ture of three-fourths dephlogiftieated air and one-fourth fixed 
air fhould coincide at leaf! nearly with the abfolute weight of 
an equal bulk of common air ; but in fact it is very far from 
it: for four cubic inches of common air weighed 1,54 gr.; 
but a mixture of three cubic inches of dephlogiftieated air and 
one of fixed air weighs 1,83 gr. ; neither indeed has fo large a 
portion of fixed air been ever fuppofed to exift in common air. 
Befides, if fixed air pre-exifted in common air, it might be fepa- 
rated from it by lime-water, at leaft in fome degree. I have 
mixed one part of fixed air with twenty of dephlogiftieated air, 
and aifo with twenty of phlogifticated air in clofe veflels, add 
thefe mixtures did not fail to render lime-water turbid. But let 
common air be agitated in lime-water ever fo long in clofe 
veftels, not the leaft cloudinefs will appear ; nor does quick-litne, 
in thefe circumftanees, in the leaft afFe£l common air, as Dr. 
Priestley has obferved. 2 fr. 184. The fpontaneous pre- 
cipitation of lime-water arifes therefore from an accidental dif- 
fufion of fixed air through common air, and the fiownefs of 
this precipitation fhews its quantity to be very fmall. The in- 
ference from the above experiments will be much ftronger 
againft the pre-exiftence of fixed air in fefpirable air, if, inftead of 
common air, dephlogiftieated air be ufed ; for there the dimi- 
nution is fo great, and the quantity of fixed air produced fo 
confiderable, that it can by no means be fuppofed to' have pre- 
exifted, its properties being fo very oppofite to thofe of deV 
phlogifticated air. 
To 
