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profecute thefe inquiries as much as my leifure from 
other purfuits will admit. I am, See. 
S you are pleafed to intereft yourfelf in my expe 
ments, I hope it will give you fome pleafure to be 
informed, that, I think, I never was more fuccefsful than 
I have been in the few days that I have been able to at- 
tend to thefe matters, fince my return into the country. 
By the heat of the flame of a candle, and catching the 
air that arifes in the manner deferibed in fig. VIII. pi. 2. 
in my late Treatife, I get the pure air I difeovered in Lon- 
don in great plenty, from a variety of cheap materials; 
not only from red lead, but many earthy fubftances 
moiftened with fpirit of nitre and dried, as chalk and 
quick-lime; which demonftrates that red lead, mercu- 
rius calcinatus per Je^ &c. extradl the nitrous acid from 
the air ; and that this acid is the mofi: eflential among the 
various ingredients which compofe the atmofphere. F rom 
tobacco-pipe-clay, and fome other things, moiftened with 
fpirit of nitre, I get fixed air; which feems to prove that 
this fpecies of air (which is a kind of acid) is a modification 
of the nitrous acid, and in fome meafure accounts for the 
LETTER II. 
TO THE REV. DR. PRICE, F. R. S 
DIAR SIR 
April I, 1775 
exigence 
