, Mr, Cavenpisn’s' Experiments on Air, ror 
nitrous.and vitriolic acids; that the metallic calces conSft of 
the metals themfelves united to the fame fubftance, commonly, 
however, with a mixture of fixed airs that’ on expofing the 
calces of the perfect metals to a iufficient heat, all the déphlo- 
gifticated air is driven off, and the calces are reftored to their 
metallic form; but as the calces of the imperfe metals are 
vitrified by heat, inftead ef recovering the metallic form, it: 
fhould feem as if all the dephlogifticated air could not be driven 
of from them by heat alone. In hike manner, according to 
this hypothefis, the rationale of the produ&tion of dephlogifti- » 
cated air from red precipitate is, that during the folution of 
the quickfilver in the acid and the fubfequent calcination, the 
acid is decompounded, and quits part of its dephlogifticated air 
tothe quickfilver, whereby it comes over in the form of nitrous 
air, and leaves the quickfilver behind united to dephlogiftica- 
ted air, which, by a further increafe of heat, is driven off, 
while the quickfilver re-aflumes its metallic form. In pro- 
curing dephlogifticated air from nitre, the acid 18 alfo decom- 
pounded ; but with this difference, that it fuffers fome of its de- 
phlogifticated air to efcape, while it remains united to the alkali 
itfelf, in the form of phlogifticated nitrous acid. As to the 
production of dephlogifticated air from plants, it may be faid, . 
that vegetable fubftances confift chiefly of various combina- - 
tions of three different bafes, one of which, when united to 
dephlogifticated air, forms water, another fixed air, and the 
third phlogifticated air; and that by means of vegetation each 
of thefe fubftances are decompofed, and yield their dephlogifti- 
cated air; and that in burning they again acquire dephlogifti- 
cated air, and are reflored to their priftine form. 
‘It feems, therefore, from what has been faid, .as if the phe-— 
nomena of nature might be explained very well on this princi- 
5 ciple, 
