TECHNIQUE FOR METABOLISM DURING REST. 101 



very large amount of soda-lime, and provision for taking care of the 

 intense heat of reaction between carbon dioxide and soda-lime. It 

 became necessary, therefore, to provide for an accurate aliquoting of 

 the main air-current leaving the chamber; this aliquoting device forms 

 the chief feature in our description of the group respiration chamber. 



ALIQUOTING AND ANALYSIS OF VENTILATING AIR-CURRENT. 



On the general fundamental principle that the total ventilating air- 

 current passing through the chamber should be of such a magnitude as 

 to maintain a carbon-dioxide content in the air inside the chamber of 

 not far from 0.5 per cent, several possible methods for the determina- 

 tion of the carbon dioxide in the outcoming air presented themselves. 

 Thus, one could use the long-established method of Pettenkofer and 

 Voit^ of determining the carbon-dioxide content of both the incoming 

 and outgoing air, noting the total amount of air leaving the chamber 

 through a series of meters, and computing from these the carbon di- 

 oxide produced inside the chamber. This would require complicated 

 gas analysis which, if possible, it is desirable to eliminate. Our success 

 with the universal respiration apparatus and its train of purifiers, con- 

 sisting of soda-hme bottles and sulphuric-acid bottles of the Williams 

 type, naturally led to an attempt to employ this thoroughly-tested 

 train in connection with the analysis of the air leaving the chamber. 



GENERAL PRINCIPLE OF METHOD FOR ALIQUOTING AND ANALYSIS. 



The apparatus as finally developed is based upon the following prin- 

 ciple : First, the air leaving the chamber is delivered into a copper box 

 or wind chest, provided with three circular openings. Two of these 

 openings have diameters exactly alike. The other may be adjusted 

 to size, either by an iris diaphragm or still more accurately with a 

 series of metal disks with circular openings of definite, known size. 

 The air leaving this wind chest escapes either into the room or into a 

 vessel in which it may be collected. Since the free discharge from this 

 wind chest is a prerequisite, some device must be attached to insure 

 that the air passing through the two small openings will be discharged 

 against atmospheric pressure. Furthermore, as the air leaving these 

 small openings is to be used for sampling, the sampling cans into which 

 the air is delivered should be provided with some means for removal of 

 the air as rapidly as it is delivered, so as to insure atmospheric pressure 

 in these cans. 



Extended experience has shown that, as used with the universal 

 respiration apparatus, the standard size soda-lime and Williams bot- 

 tles are extraordinarily efficient in removing from an air-current both 

 water vapor and carbon dioxide for long periods of time. These may 

 be used for a ventilation as high as 100 liters per minute, as is done in 



1 Pettenkofer and Voit, Ann. d. Chem. u. Pharm., 1862, Supp. Bd. II, pp. 1 and 52. 



