2 Mr. Milner on the Production of 
heat, as has been obferved, be inftantly decompofed ; but if 
the effeCt* of the union be nitrous air, that will fuftain the heat 
without decompofttion. How it happens, that nitrous air fliould 
be formed, and not nitrous acid, or what the reafon is, that 
nitrous air can fuftain a red heat without decompoiition, 
when nitrous acid cannot, 1 am unable to lay ; and it is better 
to acknowledge our ignorance than advance groundlefs con- 
jectures. So much, I think, may be pronounced as certain, 
viz. that nitrous air contains lefs dephlogifticated air than ni- 
trous acid; becaufe it requires the addition of dephlogifticated 
air to become nitrous acid. 
And, laftly, if I miftake not, the experiment with the cal- 
cined alum proves, that, in order to produce nitrous air, it is 
not fufficient merely to apply volatile alkaline air to a fab- 
fiance which is adually yielding dephlogifticated air. 
Perhaps the prefence of another fubftance is required, which 
has a ftrong attraction for phlogifton. Perhaps, in the experi- 
ments with the calces of manganefe and of iron, the inflam- 
mable principle of the volatile alkali combines with the calces 
of the metals, and the phlogifticated air, the other component 
part, unites with the dephlogifticated air; and if fo, it feerrts 
not improbable to iuppofe, that when alum is made ufe of, 
the inflammable principle of the volatile alkali having little or 
no attraClion for clay, the bafts of the alum, ftiould combine 
with its acid and form fulphur. If this reafoning be true, 
then it follows, that the vitriolic acid has a ftronger affinity to 
the inflammable principle than it has to phlogifticated air ; and 
the procefs with the green vitriol and manganefe is to be ex- 
plained by the operation of a double affinity : the inflammable 
principle of the volatile alkali joins with the calx of iron, the 
bafts 
