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VI. 
Of nitrous Apr. 
Ever fince I firft read Dr. Hales’s moft excellent 
Statical Effays, 1 was particularly ftruck with that 
experiment of his, of which an account is given, 
Vol. I. p. 224, and Vol. II. p. 280 ; in which 
common air, and air generated from the Walton 
pyrites, by fpirit of nitre, made a turbid red mix- 
ture, and in which part of the common air was ab- 
forbed ; but I never expected to have the fatisfa&ion 
of feeing this remarkable appearance, fuppofing it to 
be peculiar to that particular mineral. Happening 
to mention this fubjedt to the Hon. Mr. Cavendifh, 
when I was in London, in the fpring of the year 
1772, he faid that he did not imagine but that 
other kinds of pyrites might anfwer as well as that 
which Dr. Hales made ufe of, and that probably 
the red appearance of the mixture depended upon 
the fpirit of nitre only. This encouraged me to 
attend to the fubjeft ; and having no pyrites, 1 be- 
gan with the folution of the different metals in fpirit 
of nitre, and catching the air which was generated in 
the folution, I prefently found what I wanted, and 
a good deal more. 
Beginning with the folution of brafs, on the 4th of 
June 1772, I fxrft found this remarkable fpecies- of 
air; one effeft of which, though it was cafually ob- 
served by Dr. Hales, he gave but little attention to ; 
and which, as far as I know, has- palled altogether 
unnoticed fince his time, infomuch that no name has 
been .given.’ to it. I therefore found.myfelf, contrary 
