236 COMPARISONS OF RESPIRATORY EXCHANGE. 



sorbed by potassium-hydroxide solution and the amount found com- 

 pared with the amount determined by an analysis of the proportional 

 sample. The amounts of carbon dioxide obtained were 520.6 c.c. and 

 524.7 c.c., respectively. The whole method has been tested by Zuntz 1 

 with burning candles, the experimental procedure being the same as in 

 an ordinary respiration experiment. The average error found in the 

 oxygen determination was 0.40 per cent and in the carbon-dioxide 

 determination 2.15 per cent. 



Schaternikoff 2 states that the method of measuring the volume of 

 air by means of a meter, when the air is being pushed through it inter- 

 mittently, is liable to error because the inertia of the moving drum 

 causes it to record more than the true volume. 



Calibrations of the Elster meter were made in this investigation, 

 in which air or oxygen was driven through it in exactly the same man- 

 ner as in a respiration experiment. These calibrations gave factors for 

 correction of 101.8 per cent and 100.8 per cent with continuous flow and 

 100.9 per cent with intermittent flow, these errors being no larger than 

 would be expected in individual calibrations. In all probability, the 

 measurement of the expired air by the Elster meter is accurate to within 

 1 or 2 per cent. 



The level of the water in the Elster meter is of prime importance. 

 To secure trustworthy results, it is essential that the meter should be 

 level as any slight variation in the level of the water makes an appre- 

 ciable difference in the results. In this laboratory we have installed on 

 the outside of the meter a water-gage with a millimeter scale, by means 

 of which the exact height of the water inside the meter can be noted 

 at any time. 



The Zuntz-Geppert gas-analysis apparatus can be made to give 

 results which agree very well, particularly if that form is used in which 

 the burettes are divided into 0.02 c.c. The manipulation of the 

 Zuntz-Geppert gas-analysis apparatus is somewhat difficult, and it will 

 be noted from the statistics 3 of the experiments that in some of the 

 comparisons with the Zuntz-Geppert method this gas-analysis appa- 

 ratus was not used, but that the Haldane apparatus was substituted. 



An advantage in using the Zuntz-Geppert gas-analysis apparatus 

 is the fact that duplicate analyses may be carried out simultaneously, 

 thus assuming identical conditions. This, however, insures only 

 uniformity in the technique, but does not guarantee the accuracy of the 

 technique or of the results. It has been my experience that it is more 

 difficult to obtain duplicate results with any method when the deter- 

 minations are made at different times than when they are all made at 



*Zuntz and Hagemann, Landw. Jahrb., 1898, 27, Supplm. in, p. 10. 



2 Schaternikoff, A new method for determining the quantity of exhaled air in man and the 

 quantity of carbon dioxide contained in it. (Russian.) Dissertation, 1899, Moscow. 

 3 See p. 129. 



