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fore, we are taught, that, when black blood assumes 
a red colour by being thus placed in a moistened blad- 
der, and exposed to atmospheric air, the air itself, at 
the same time, undergoes a change ; for its volume 
is diminished, and carbonic acid is produced. 
585. To ascertain these facts with greater precision, 
we put another quantity of black blood into a small 
bladder, and suspended it, as before^ from the top of 
a small jar inverted in mercury, and which contained 
18^3 cubic inches of atmospheric air. Under this 
jar, also, a small cup of solution of potassa was pla- 
ced. The blood, as before, was soon reddened, and 
the jar became dim. In two days, the mercury had 
risen nearly half an inch into the jar, and, by the 
close of the fourth day, it stood seven-eighths of an 
inch high, where it remained for some time quite 
stationary. On analysing the residual air, it was 
found to suffer no change, either from agitation with 
lime water, or by being exposed to the contact of 
phosphorus ; so that, though all the oxygen had dis- 
appeared, no carbonic acid was present, but that gas 
was entirely attracted by the water of potassa em- 
ployed. 
586. The capacity of the jar, in the above experi- 
ment, has been stated to be equal to 18.3 cubic 
inches ; and the bladder, with its contents, together 
with the cup and solution, we found to occupy a 
space equal to 5.2, which reduces the actual bulk of 
air, employed in the experiment, to 13.1 cubic in- 
ches. The mercury which, in consequence of the 
attraction, of the carbonic acid, had risen seven-eighths 
of an inch into the jar, occupied a space equal t* 
