132 A CHEMICAL SIGN OF LIFE 
the nitrometer C. Increase the pressure inside of the 
nitrometer C by raising the safety bottle D above the 
level of the alkali in the nitrometer, and then open 
stopcock J. In this way the excess of mercury left 
in the capillary tube will be pushed over into the 
chamber A and flow through stopcock 4 into a receiv- 
ing vessel. 
If stopcocks 2 and 3 are absolutely air-tight, there. 
should be no air bubble present in the tube B on standing. 
This being assured, a known amount of mercury is intro- 
duced into the chamber A by means of mercury burette 
H, thus making the capacity of the chamber what was 
desired. Tissue is introduced into the chamber in the 
usual manner, the glass stopper is replaced, the chamber 
is sealed with mercury, and the nitrometer is filled with 
air free from carbon dioxide. After evacuation of the 
chamber and introducing pure air several times, stop- 
cock 5 is closed and the time is recorded, the pressure is 
adjusted, and stopcock 2 is turned 45°. At the end of 
the desired period of respiration any portion of the air, 
say 10 or 15 c.c., from the chamber can be driven into 
tube B. This is accomplished by raising the right-hand 
mercury burette H and by simultaneously opening 
stopcocks 2 and 4 and gradually lowering the left-hand 
mercury burette G. Stopcock 2 is now closed and the 
pressure of the air in B is made equal to that of the 
atmosphere and is kept under this condition, having 
the mercury burette G at the proper height. 
Remove mercury from the stopper S and unstop the 
chamber, take away the tissue, and lower the mercury 
burette H so that all the mercury in the chamber will 
flow back into the burette. The little excess of mercury 
