CRITICAL DISCUSSION OF RESPIRATION APPARATUS. 237 



exactly the same time. It is therefore a better control of a method to 

 make the duplicate determinations at different times and preferably 

 on different days. I have always more confidence, for example, in the 

 results of analyses of a sample of expired air when the second analysis 

 is made on a different day than when the two analyses are made simul- 

 taneously or even immediately succeeding one another, provided the 

 sample is stored in such manner as to prevent loss of carbon dioxide. 



One serious objection to the Zuntz-Geppert gas-analysis apparatus 

 is the fact that the gases are collected over water. Many experiments 

 of various kinds in this laboratory have shown that the collection or 

 storage over water of air containing carbon dioxide is a very bad prac- 

 tice, for even during the time of collection, i.e., 15 or 20 minutes, there 

 is a possibility of a slight disappearance of the carbon dioxide, which 

 does not occur when the gas is collected over mercury. Magnus-Levy 1 

 cites experiments which were carried out by Zuntz and Hagemann in 

 which it was demonstrated that the analyses of expired air collected 

 over mercury and over water gave, on the average, the same results; 

 but the variations in the results obtained in analyzing carbon dioxide 

 collected over water are considerable and it is questionable whether 

 results varying so widely show that the method is a good one. While 

 it may be possible that air collected in the burettes of the Zuntz- 

 Geppert gas-analysis apparatus and analyzed immediately suffers 

 no significant loss of carbon dioxide, there is no question that air 

 collected over water in glass samplers and analyzed later would lose a 

 part of its carbon dioxide, and that such analyses would not give accu- 

 rate results. This is particularly true if the samples are stored for 

 12 hours or more; the losses are then very large, and occur even when 

 there is no water visible in the container. Even saturated air, collected 

 in dry glass containers or over mercury, loses carbon dioxide if the 

 samples are kept for several days, but the loss is not great enough to 

 affect results in work on the respiratory exchange. The practice of 

 collecting samples over water and then storing them for analysis 

 must certainly be avoided in all respiration work in which the highest 

 degree of accuracy is desired. 



Durig 2 has pointed out a possibility of error in the determination of 

 oxygen by the Zuntz-Geppert gas-analysis apparatus in that even 

 when constant results are obtained after absorption by phosphorus 

 it is possible that the oxygen is not all absorbed. He mentions par- 

 ticularly the fact that when time is limited there is a tendency for 

 operators to neglect the last particle of absorption. The use of phos- 

 phorus in gas-analysis apparatus is by no means to be discouraged, 

 however, in spite of this possibility. In our use of the Haldane appa- 



^agnus-Levy, Archiv. f. d. ges. Physiol., 1894, 55, p. 20. 



2 Durig, Denkschriften der mathematisch-naturwissenschaftlichen Klasse der kaiserlichen 

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



