OXYGEN RESPIRATION 29 



A light wash bottle filled with concentrated sulphuric acid 

 must be inserted behind the potash apparatus if the gas stream 

 passes through sulphuric acid in front of the potash apparatus. 

 Only thus is it possible to preserve a constant weight of water 

 in the absorption apparatus. A second potash apparatus filled 

 with concentrated sulphuric acid will serve as a weighable wash 

 bottle. It is still simpler to place some asbestos soaked in cone, 

 sulphuric acid in the calcium chloride tube of the potash 

 apparatus. In this case the calcium chloride tube must be 

 freshly filled for every experiment. Behind all the above 

 absorption vessels there must be inserted a wash bottle with 

 sulphuric acid in order to avoid a direct connection between the 

 moist air of the air pump and the absorption vessels. 



The results of C02-determinations in the Geissler potash 

 apparatus filled in this manner are very accurate. With care 

 it is possible to determine fractions of a milligram with a fair 

 degree of certainty. Weighed soda lime tubes are no less 

 reliable and are perhaps still simpler to use. Small U-tubes 

 with ground glass stoppers are the best to use and are prepared 

 with not too dry soda lime (see previous note). Two U-tubes 

 are inserted one after another. The second tube must show no, 

 or only a very small, increase in weight. To dry the gas stream, 

 cone, sulphuric acid is used here also. As to the general han- 

 dling and weighing of the potash apparatus and soda lime tubes, 

 handbooks of analytical chemistry must be consulted. During 

 each experiment all apparatus and wash bottles are connected 

 by rubber tubing. Before and behind the potash apparatus or 

 soda lime tube a screw pinchcock is applied. The current of 

 gas is regulated by means of the pinchcock opening behind the 

 potash apparatus. The other pinchcock is left open except to 

 interchange the potash apparatus when both are closed, the 

 potash apparatus removed and replaced by another which is 

 prepared with fresh KOH and weighed. 



If one is to follow the progress of respiration more accurately 

 by means of rapid, successive COo-determinations. and eventu- 

 ally to plot them, a continual interchange and weighing of 

 potash apparatus or soda lime tubes proves to consume con- 

 siderable time. For such experiments one uses for the most 



