THE PHENOMENA OF HUMAH RESPIRATION. 
13 
Bj this means the agitation could be made at will, either below the atmospheric 
pressure, at that jDressure, or above it. 
On depressing the plunger to 50 c.c. the air after complete combination was very 
nearly under atmospheric pressure. On depressing the plunger to 100 c.c. the pressure 
amounted to very nearly 38 mm, of mercury. On depressing it to 80 c.c. the pressure 
amounted to nearly 23 mm. of mercury. 
It was found that the combination took place much more rapidly at a pressure 
exceeding that of the atmosphere than below or at the atmospheric pressure. 
In ordinary circumstances the absorption of 50 c.c. in the cylinder, from expired air 
under analysis, would cause a vacuum or fall of pressure of about 38 mm. of mercury. 
This circumstance militates strongly against complete absorption, but by increasing 
the pressure as stated above to 23 mm. over and above the atmospheric pressure 
(after absorption), it was found that after agitating for 10 minutes no COn was left 
uncombined, and with a pressure of 38 to 40 mm. the combination appeared complete 
after acfitatino- for 5 minutes. 
In the course of the present inquiry the use of the plunger was given up,"^' and the 
air in the cylinder was compressed b}" driving into it about 100 c.c. of common air, free 
from carbonic acid. This was done with a pear-shaped vulcanised india-rubber bag 
attached to the end of one of the terminal tubes, as shown in the accompanying 
drawing. The air was forced into the cylinder with the hand, the stopcock again 
closed and the bag removed. Thus, a volume of about 100 c.c. of air, free from COo 
(passed through pumice stone moistened with potassium hydrate), was introduced into 
the cylinder, producing after combination a pressure of about 38 mm. of mercury. 
After shaking for a quarter of an hour, the bottle containing the milky alkaline 
solution was unscrewed from the cylinder and its contents were rapidly poured into 
a dry glass-stoppered bottle of a capacity of about 100 c.c., which was sealed with 
paraffin. The next day the precipitate had separated, and the clear fluid was titrated 
with a solution of oxalic acid of such a strength that 1 c.c. corresponded to 0 001 
mgr. COo. 
Fourteen experiments were undertaken to test the accuracy of this aaialytical 
method. In each experiment two analyses were made from the same stock of air 
in the bell-jar, and the accuracy of the results goes far to show how well the bell-jar 
retained its equilibrium with the atmospheric pressure. The results are tabulated as 
follows ;— 
* Some determinations of COj, made with the plunger, by PetteXkofer's method, have reqiTired a 
small correction owing to the plunger coming ont slightly greasy from the stuffing box. A number 
of experiments showed the collection to amount to a mean of 1 per cent. 
