t 



THE RESPIRATION APPARATUS. 31 



ever, the actual efficiency falls far short of these figures, and under the 

 most favorable conditions only about 400 grams can be absorbed. 

 While this efficiency is very far from the theoretical, it is none the less 

 remarkably good, considering the conditions under which the absorp- 

 tion takes place, /. e., a solid absorbent limited to surface absorption 

 only, and indicates that the apparatus is well adapted for the absorp- 

 tion of a relatively large amount of carbon dioxide from a rapidly 

 moving current of air. 



The efficiency of the absorber has been found to depend very largely 

 upon the rate of evolution of carbon dioxide. In the alcohol check 

 experiments and in rest experiments with men, where the rate of evo- 

 lution of carbon dioxide is fairly constant and does not exceed 50 to 60 

 grams per hour, the soda lime is more completely exhausted than in 

 work experiments with men, where the amount of carbon dioxide may 

 rise to 200 grams per hour. With this large quantity of carbon dioxide 

 passing through the absorber system, the reaction between the soda lime 

 and the carbon dioxide is so intense that the cans become very much 

 heated. The soda lime seems to fuse or cake on the edges, and the in- 

 terior of each section of soda lime is thereby partially protected from the 

 action of the carbon dioxide. Under such conditions it is found that 

 each can will not, as a rule, take up much more than from 100 to 125 

 grams of carbon dioxide before it is necessary to change. Further- 

 more, all three cans in the system, shown in figure 5, during a two- 

 hour period when the man is at hard work, take up approximately the 

 same amount and all become heated. While it is possible to use these 

 partially exhausted cans during the night period, when the subject is 

 at rest and the rate of evolution of carbon dioxide at a minimum, it is 

 not found safe to use such a partially exhausted can during a second 

 work period ; consequently the can is opened and the soda lime re- 

 moved. It is found on removing the different sections of the soda lime 

 that instead of adhering in a solid white cake, as is the case when the 

 soda lime is completely exhausted (see fig. 12), it crumbles and falls 

 apart, except where the partial fusion or caking has taken place. By 

 picking out the larger lumps of the partially fused material ' the major 

 portion of the unused material can be saved and used to refill the cans. 

 In this way the efficiency of the soda lime is not impaired, and the total 

 amount of carbon dioxide absorbed by a given weight of soda lime need 

 not, under such manipulation, fall much below the maximum amount 

 under the most favorable conditions. 



*By "partially fused" it must not be understood that the temperature of the 

 soda lime rises to anything like the fusing point of soda lime, but that there 

 is an appearance not unlike fusion. 



