24 A RESPIRATION CALORIMETER. 



The cold air which settles in the bottom of the aluminum shields 

 cools them so noticeably that frequently they, too, begin to condense 

 water on the outside. To collect this water another trough, or, more 

 properly speaking, gutter (Dt in fig. 33), is attached to the bottom of 

 each shield to conduct the water dripping from the aluminum trough 

 to a proper container (Dc in fig. 33). 



The shields do not encompass the heat-absorber pipes at the corners, 

 as may be seen in figure 33. It was frequently found, however, that 

 the copper pipe became coated with moisture and the water thus con- 

 dens ed dropped to the floor of the chamber. To collect this moisture 

 the drip-cans into which the water from the troughs is emptied are 

 suspended from the copper pipe at the corners and are of such shape 

 that they catch any water that drips from the pipe. The water may 

 be drained from these cups into bottles and weighed. 



To determine the total quantity of water thus condensed it is neces- 

 sary to know how much remains on the surface of the heat absorbers not 

 collected as drip. For this purpose provision is made for weighing the 

 whole heat-absorbing system, as explained elsewhere. 



REMOVAL OF WATER VAPOR FROM THE AIR CURRENT. 



The problem here is the removal of a large amount of water vapor 

 from an air current flowing at the rate of 75 liters per minute. For 

 this purpose the air is caused to pass through concentrated sulphuric 

 acid in a specially devised container. From numerous preliminary 

 experiments it was learned that none of the common solid absorbents 

 for water, such as calcium chloride and phosphorus pentoxide, could 

 be relied upon to remove water from a large air current as completely 

 as does the acid. 



DESCRIPTION OF THE WATER-ABSORBERS. 



The difficulty with using sulphuric acid as the absorbent is that it is 

 next to impossible to obtain a satisfactory container for it other than 

 glass, and it was feared that the large size of the absorber would make 

 a glass vessel so unwieldy that it would be readily broken. A large 

 number of experiments were made testing the resistant powers of copper, 

 aluminum, hard rubber, gold-plated copper, and various enameled wares. 

 As the result of these tests it was found that enameled iron resisted the 

 action of the strong sulphuric acid admirably, and a set of absorbers 

 made from this material was in use for over a year. It was, however, 

 impracticable to construct a form of absorber from this material of fewer 

 than two parts, and equally impossible to join the two parts so as to 

 prevent permanently leakage of air. Consequently the use of enameled 

 ware was abandoned. 



