co Mr. Kirwan’s Remarks on 
air contains fearce any fixed air; is it not apparent that’ the 
fixed air thus found was generated by the very a& of calcination, 
by the union of the phlogilton of the metal with the dephlo- 
gifticated part of the common air, fince after the operation the 
metal is deprived of its phlogifton, and the air of its ee 
gifticated part ? 
But Mr. Cavenpisy objects, that no one has extracted sista 
air from metals calcined in clofe veflels. To which I anfwer,; 
that this further proof is difficult, and no way neceflary ; itis — 
difficult, becaufe the operation can eafily be performed only on 
{mall quantities ; it is unneceflary, becaufe it differs from the 
operation in open air only by the quantities of the materials 
employed, in every other refpect it 1s exactly the fame. Since 
Mr. CavenpisH fufpects the refults are different, it is incum- 
bent on him to thew that difference; but until then, accord-— 
ing to Sir Isaae Newton’s fecond rule, to natural effects of 
the fame kind the fame caufes are to be afigned, as far as it may 
be done, that is, until experience points out fome other caufe, 
Tt may further be urged, that precipitate per fe yields only 
dephlogifticated air, that minium alfo yields a large proportion 
of it. This difficulty I have formerly anfwered by afferting, » 
that thefe calces are in fact united only to fixed air, and that 
they yield dephlogifticated air, merely becaufe the fixed air is 
decompofed by the total or partial revivification of the metallic 
fubftances; this 1 think may be demonftrated by the following 
experiments. Let fublimate corrofive fingly be treated in any — 
manner, it will not yield dephlogifticated air (4 Pr. 240.) 3 but 
Jet a folution of fublimate corrofive be precipitated by a mild 
fixed alkali, this precipitate wafhed, dried, and diftilled in a 
pneumatic apparatus, will yield dephlogifticated air, and the 
mers 
