the heavy inflammable Air . 71 
Objects are often too common or too near for our obferva- 
tion. Phlogifticated air prefents itlelf in the decompofition 
of fo many bodies, that its appearance excites no enquiry ; 
and it is not regarded as eflential to the chemical conftitution. 
of the bodies which yield it, excepting in the inftances of ni- 
trous acid and volatile alkali, two fubftances of very fmall 
extent in the fcale of natural bodies. The calces of metals 
are well known to contain phlogifticated air; yet the effect of 
this air on calcination in general, and how far the very different 
calces of the lame metal are influenced in colour or other pro- 
perties by the different proportions of phlogifticated air, has never 
been confidered. Fixed air is often formed from the calces of 
metals, mixed with water, or with fome other fubfbmce contain- 
ing light inflammable air Red precipitate mixed with iron 
filings yielded very pure fixed air. Brafs duft mixed with red 
precipitate, likewife gave out fixed air, though in lefs quan- 
tity. Turbith mineral and iron filings, treated in the fame 
manner, afforded much lefs fixed air than the red precipitate 
and iron filings. It is probable, that the turbith mineral contains 
lefs phlogifticated air, than the red precipitate. The fixed air 
in all thefe experiments was mixed with phlogifticated and de« 
phlogifticated air. Mr. Kjrwan t found, that the fimple 
calx of mercury with iron filings and water produced fixed air# 
The fame author alfo obferved, that iron calcined with nitrous- 
acid gave out, upon being heated, fixed air; and he found the 
production of this air renewed upon the addition of water. 
Dr. Pr 1 3 stley j obtained fixed air from iron converted into 
ruft by expoiure to nitrous air. In all thefe experiments the 
* Priestley* VI. p. 253, 254. 
f Eflay on Phlogifton, p. 114, 
$ Ibick p. 52. 
three 
