130 _ Mr, Kirwan’s Reply, &c. 
grains of bar iron contain, according to Mr. BeErcmaw, at moft, 
two-tenths of a grain of plumbago; and confequently 1000 grs. 
of this iron contain but two grains of plumbago ; and plumbago, 
according to Mr. ScHEELE, contains but one-third of its weight 
of fixed air; fo that here, fuppofing the plumbago to be de- 
compofed, we can have at moft but feven-tenths of a grain of 
fixed air, or little more than one cubic inch. If we fuppofe 
the filings to be from fteel, 1000 grains of fteel containing 
eight of plumbago, we may have about 2,5 of fixed air, or 
about 1,5 cubic inch, and this is the ftrongeft fuppofition, 
and the moft favourable to Mr. Cavenpisu. What fhall we 
then fay, if we confider that thefe filings were mixed with 
copper or brafs which contain no plumbago? and, above all, 
that plumbago cannot be fuppofed decompofable by red preci- 
pitate, fince even the nitrous acid cannot decompofe it ? 
sthly, With regard to the power which nitrous felenite has 
of abforbing fixed air, I muft allow the experiments of Mr. 
CavenpisH to be juft and agreeable to my own; but it only 
follows, that when fixed air is in its na/cent ftate, it is more 
abforbable. ‘Thus many metallic calces take it from alkalies 
in its mafcent ftate, though in other circumftances they will 
take none. 
Laftly, the permanence of a mixture of nitrous and come 
mon air, made over mercury, cannot be attributed to nitrous 
vapour, as vapour is not elaftic in cold; befides, I have often 
made the mixture without producing any fuch durable vapour, 
and this will always happen, when the nitrous air is made from 
nitrous acid fufficiently diluted. 
Wane 
wh Re 
