[ 3^1 ] 
twelve inches in diameter; and the ufe of it has rnore 
than anfwered my highell expe<^i;ations. The man- 
ner in which I have ufed it, has been to throw the 
focus Upon the feveral fubftances I wifhed to exa- 
mine, either in vacuo, or when confined by quickfil- 
ver, in veflels filled with jthat fluid, and ^Handing ^ith 
their mouths rmmerfed in it, I prefently found that 
different fubftances yield very different kinds of air by 
this treatment; and though the reafons,,or analogijg^rpf 
the different produdts, in many of the cafes, be fufli- 
ciently obvious, and fuch as I had conjectured a pridri, 
yet in other cafes I am not a little puzzled and furprized. 
Various metals yield inflammable air, by this procefs ; fe- 
veral faline fubftances yield fixed air; many metallic 
calces yield the fame, and fome of them a phlogiJHcated 
common air; and fome of the precipitates, in which the 
nitrous acid was employed, yield nitrous air, in one or 
other of its forms. But the moft remarkable of all the 
kinds of air that I have produced by this, prqpefs is, one 
that is five or fix times better than common air, for the 
purpofe of refpiration, inflammation, and, I believe, 
every other ufe of common atmofpherical air. As I 
think I have fufliciently proved, that the fitnefs of air for 
refpiration depends upon its capacity to receive the phlo^ 
gijion exhaled from the lungs, this fpecies may not im- 
properly be called, dephlogijlk^l^d air. This fj^ecies of 
air I firft produced from mercurius calcinatus per fe, then 
from the red precipitate of mercury, and now from 
red lead. The two former of the fubftances yield it 
pure; 
