OXYGEN RESPIRATION 47 



bulb m and opening the glass stopcock /. As a result the mer- 

 cury in the manometer tube h of the flask rises to a certain level. 

 The stopcock / is now closed, the bulb I is connected with the 

 tube g by a suitable turn of the three-way stopcock r, the pear- 

 shaped bulb m is elevated, the stopcock / is opened, and the 

 last trace of gas is driven out of the bulb and the tube. After 

 closing the stopcock /, the bulb / is again connected with the 

 tube h and this tube and the attached vertical arm a of the 

 flask tube are filled with mercury. The necessary manipula- 

 tions are intelligible from the explanation above: the pear-shaped 

 bulb m is raised and the stopcock/ is opened. The experimental 

 flask is now perfectly sealed as shown in the figure. The 

 barometer reading and the level of mercury in the manometer 

 tube are noted and the experiment begins therewith. This 

 sealing of the flask is really very simple. After a little practice 

 it is easily and safely performed in less time than when it is 

 necessary to follow the above explanation. 



The experiment proper consists in withdrawing, from time 

 to time, test portions of gas from the experimental flask as 

 described above, and in passing them through the tube g into 

 the analysis tubes completely filled with mercury. This pro- 

 cedure is entirely analogous to the original closing of the flask 

 except that in the latter case the gas sample is not kept for 

 analysis. 



The gas analysis yields the percentage content but not the 

 absolute amounts of the single components of the gas mixture 

 which is being studied. These are needed, however, for the 



determination of the magnitude of ^- The calculation of 



CO 



^^ is based on the fact that in respiration there is neither 



O2 



an absorption nor a liberation of nitrogen. We assume that 

 a is the percentage of COo, b is the percentage of oxygen, 

 and c is that of nitrogen and other inert gases in the gas mixture 

 just analyzed. Let it be further known that at the beginning 

 of the experiment the air inclosed in the container had a normal 

 composition (O2 = 20.9%; N. = 79-i%)- If ^ is not exactly 

 79.1 the total volume of the gas mixture (reduced to normal 



