TECHNIQUE FOR METABOLISM DURING REST. 113 



alterations in the tension of the spiral spring may be made without the 

 necessity of altering the position of the contacts materially. 



Occasionally, through error or otherwise, the blower delivering air 

 to the wind chest is connected before the rubber stoppers^ in bi and &2 

 are removed. There is then a great distention of the diaphragm with a 

 tendency to lift the rods so that the contact slips out from between the 

 two small disks {di and ^2, fig- 13). To prevent this a third disk, d^, is 

 attached to the rod below the cross arm support in such a manner that 

 the rubber diaphragm can not be raised sufficiently to do any harm to 

 the contacts. It has been found advantageous to insulate all the parts 

 by means of fiber washers. Hard-rubber bushings are placed in the 

 top cross-arm, which insulate the entire electrical system from the 

 table. 



It is thus seen that we have provided a means for removing air from 

 the sampling cans as fast as it is delivered, to maintain absolute and 

 uniform atmospheric pressure inside them, to insure uniform discharge 

 of air from the wind chest through the two 10-mm. openings and, 

 furthermore, to drive the respective volumes of air withdrawn from the 

 sampling cans through suitable purifying vessels to remove the water 

 vapor and carbon dioxide. The absorption of the carbon dioxide and 

 the weighing of the purifying vessels still remain to be described. 



QUANTITATIVE ABSORPTION OF CARBON DIOXIDE. 



The complete removal of the carbon dioxide from the air sample and 

 the provision for its quantitative measurement are accomplished by the 

 standard soda-lime bottles and Williams bottles employed in this labo- 

 ratory for all universal respiration apparatus. If the soda-lime bottle, 

 L, and its accompanying Williams bottle, M (see fig. 8), are weighed 

 prior to the period and again subsequent thereto, the increase in weight 

 of the two indicates the carbon dioxide absorbed during the time, for 

 the air entering L is dried over sulphuric acid in Ji and J2 and the air 

 leaving M is dried to the same degree of humidity. The duplicate set 

 of bottles shown in figure 12, controlled by the valves V3 and Vi, gives 

 an admirable check upon this measurement of carbon dioxide. It is of 

 interest that almost invariably the agreement between the two sets is 

 absolute. Occasionally, when there is faulty adjustment of the pres- 

 sures inside the samphng cans, there is a sHght discrepancy, owing to 

 the fact that if the pressure is greater inside of one can than the other, 

 less air is delivered and less carbon dioxide removed. 



The determination of the amount of carbon dioxide in the aliquot is 

 thus simple, namely, the weighing of the two absorbing vessels. The 

 carbon dioxide 'collected in these vessels does not, however, represent 



* The stoppers are always in place when an experiment is in progress. 



