Comparative Air-Analyses 



97 



value at 25.8 C. and that 6 degrees higher. The low value at 17.1 C. 

 may in part be attributed to the well-known slow absorbing action of 

 potassium pyrogallate at low temperatures. From these results we may 

 safely conclude that temperature changes in the reagent are without 

 appreciable effect upon the absorption of oxygen within the limits men- 

 tioned, i.e., between 17.1 C. and 31.8 C. 



Table 58. Analyses made at the Nutrition Laboratory of air confined in a steel cylinder, 

 using high and low temperatures of water-bath. 



Errors in the third routine. Two fundamental alterations in routine 

 were introduced at this time. Miss Johnson called my attention to the 

 fact that after absorbing the oxygen, to connect the pipette B with the 

 manometer and then subsequently to send the air into the potassium 

 pyrogallate was illogical for the following reason: 



When the stop-cock a is turned so as to communicate the gas in B 

 with the manometer, there is in B only nitrogen. On the other hand, in 

 the capillary between the stop-cocks a and d there is air. During the 

 short time required to set the manometer and take the reading, there is 

 unquestionably a slight diffusion of air from the capillary into the chamber 

 B. Subsequently, when this gas is passed into the potassium pyrogallate, 

 there is a further contraction in volume which results in a considerable 

 increase in the apparent percentage of oxygen. Probably the increased 

 percentages found when the gas was repeatedly passed into the reagents 

 were due to this fact rather than to the distillation of water. It was ap- 

 parent, therefore, that before connection with the manometer is made, the 

 gas must be sufficiently in contact with the potassium pyrogallate to ab- 

 sorb all of the oxygen, and that no subsequent passage of the gas in A 

 into the reagent should be made. Accordingly the routine was so changed 

 as to secure these conditions. 



