76 COMPARISONS OF RESPIRATORY EXCHANGE. 



within 0.001 c.c. The final readings are then taken and from the dif- 

 ference between the reading after the carbon dioxide is absorbed and 

 the reading after the oxygen is absorbed, the amount of oxygen in 

 the sample is calculated. 



Absorption of oxygen by phosphorus. — In many analyses of expired air 

 and atmospheric air made in this laboratory, phosphorus instead of 

 potassium pyrogallate has been used for the absorption of oxygen. 

 The general routine is as follows: After the carbon dioxide has been 

 absorbed in the usual way, the air is sent through the upper of the two 

 right-angle stopcocks, G, into the pipette, R, which contains sticks of 

 phosphorus, and is allowed to remain there for 3 minutes. It is next 

 drawn over into the burette, A, once, then put back into the phosphorus 

 again for 1 minute, sent into the potash pipette, E, five times, and 

 finally into the phosphorus pipette, R, for 1 minute, when a reading is 

 taken. After the first reading the air is sent into the phosphorus 

 pipette for one minute and into the potash once and the second reading 

 taken. This process is repeated until the readings are constant. The 

 air is then sent over into the phosphorus pipette and at the end of 

 5 minutes the final reading is taken. The additional 5 minutes is 

 allowed to insure complete absorption, as Durig 1 has pointed out that 

 even when apparently all the oxygen has been absorbed there may still 

 be minute traces which require a longer time. 



The use of phosphorus as an absorbent has proved extremely satis- 

 factory. It has the advantage over the potassium pyrogallate that it 

 does not have to be renewed so frequently, that the meniscus of water is 

 much easier to set in the capillary connecting tube, and that the 

 absorption can be carried out without the continuous raising and lower- 

 ing of the bulb D. In order to obtain the quickest absorption with the 

 potassium pyrogallate, it is necessary to drive the gas back and forth 

 many times, and this constant raising and lowering of the mercury bulb 

 is very tiring. There is also the advantage that should the liquid over 

 the phosphorus pipette be drawn up into the connections no serious 

 harm is done, while with the potassium pyrogallate it is necessary to 

 take out all of the stopcocks and thoroughly clean them with acid 

 before the apparatus can be used again. The phosphorus pipette is 

 kept covered from the light by means of a metal shield which is taken 

 off only during analysis. In one apparatus stick phosphorus has been 

 in use for 8 months and shows no signs of deterioration. 



Comparison of potassium pyrogallate and phosphorus as absorbents 

 for oxygen. — To make sure that the results obtained by phosphorus 

 were comparable with those obtained by the absorption with potassium 

 pyrogallate, a number of comparisons on both atmospheric air and 

 expired air were carried out in this laboratory. It will be seen by 

 reference to table 10 that the results of the two series of analyses are 



1 Durig, Denkschriften der mathematisch-naturwissenschaftlichen Klasse der kaiserlichen 

 Akademie der Wissenschaften, 1909, 86, p. 119. 



