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pure ; but the red lead I have generally met with yields 
a greater proportion of fixed air along with it. Another 
quantity, however, gave this air and hardly any thing 
elfe. On what this difference depends I cannot tell; but 
hope to be able to inveftigate. That this air is of that 
exalted nature, I firft found by means of nitrous air, 
which I conftantly apply as a tefi; of the fitnefs of any 
kind of air for refpiration, and which I believe to be a 
moft accurate and infallible tefi: for that purpofe. Ap- 
plying this tefi, I found, to my great furprize, that a 
quantity of this air required about five times as much 
nitrous air to faturate it, as common air requires. Com- 
mon air is diminifiied about one-fifth, by a mixture 
of one-half nitrous air; but one quantity of this air was 
diminifiied one-half, and another two-thirds, by the ad- 
dition of twice as much nitrous air ; and three times tne 
quantity, left it little more than it was at the firft. A 
candle burned in this air with an amazing ftrength of 
flame; and a bit of red hot wood crackled and burned 
with a prodigious rapidity, exhibiting an appearance 
fomething like that of iron glowing with a white heat, 
and throwing out fparKS in all direflions. But to com 
plete the proof of the fuperior quality of this air, I in- 
troduced a moufe into it ; and in a quantity in which, had 
it been in common air, it would have died in about a 
quarter of an hour, it lived, at two different times, a 
whole hour, and was taken out quite vigorous ; and the 
remaining air appeared to be ftill, by the tefi; of nitrous 
air as eood as common air. This experiment I alfo re- 
’ peated, 
