Dr. Priestley’s Obfervations, See. \oy 
employed in forming the fixed air above mentioned* He has 
proved, indeed, that the application of dephlogifticated air to 
the outfide of a vein will change the colour of the blood con* 
tained in it. But this might have been effedted, as I firft fup- 
pofed, by the fimple difeharge of phlogifton from the blood, 
when it had an opportunity of uniting with the dephlogifti- 
cated air thus prefented to it. He does not, however, feem to 
fuppofe, that there is any phlogifton difeharged from the blood 
in the a<ft of refpiration, but only that dephlogifticated air 
enters into it. But that my former fuppofition, as well as his. 
is true, will appear, I prefume, from the experiments which I 
lhall prefently recite. 
As, in order to determine what proportion of the dephlo- 
gifticated air deftroyed by refpiration is employed in forming 
the fixed air which is the produce of it, it was neceffary to 
afeertain as exactly as pofiible the proportion of dephlogifticated 
air and of phlogifton in the compofition of fixed air, I repeated 
with particular care experiments fimilar to thofe which I had 
formerly made for that purpofe. 
I heated charcoal of copper in 41 ounce meafures of dephlo- 
gifticated air of the ftandard of 0.33, till it was reduced by wafti- 
ing in water to 8 oz. m. of the ftandard of 1.33. Again ? I heated 
charcoal of copper in 40.5 oz. m. of dephlogifticated air of the 
ftandard of 0.34 till it was reduced to 6 oz. m. of the ftan- 
dard of 1.76. And in each of thefe cafes there was a lofs of 
6 gr. of the charcoal of copper ; fo that there cannot be more 
than 6 gr. of phlogifton in 33 oz. m. of fixed air, and confe- 
quently that only a very little more than one-fourth of the 
weight of fixed air is phlogifton. 
I heated perfectly well burned charcoal of wood in 60 oz. 
of common air, and found one-fifth of the remainder to 
P 2 be 
