t 



THE RESPIRATION APPARATUS. 27 



is noted, /. e. , 100 grams less than tests have shown to be absolutely 

 safe, the spent acid is removed and replaced by a fresh supply. 



Supply of sulphuric acid. With this form of absorber for the removal 

 of water vapor from the air the use of considerable quantities of sul- 

 phuric acid is necessary. It has been found that the ordinary grades 

 of concentrated sulphuric acid, specific gravity 1.84, are admirably 

 adapted for this work. The acid is purchased in carboys and conse- 

 quently the expense for this reagent is small. 



APPARATUS FOR THE DETERMINATION OF CARBON DIOXIDE. 



As the air leaves the first water-absorber it is perfectly dry, but still 

 contains carbon dioxide and is somewhat deficient in oxygen. The next 

 step in the process of purification is the removal of the carbon dioxide. 

 For a number of years prior to the introduction of the closed-circuit 

 system soda lime of special preparation was used in this laboratory 

 for removing carbon dioxide from the air samples taken for analysis. 

 The success attending its use for this purpose was such as to suggest 

 it as a means for removing the total quantity of carbon dioxide from 

 the main ventilating air current. From the area of the ordinary 

 U tube, described on page 45, the rate and length of time of flow 

 through it, and the length and weight of the layer of soda lime, it was 

 calculated that a soda-lime container with a diameter of approximately 

 150 mm. and a length of approximately 380 mm. would be as efficient 

 in removing carbon dioxide from an air current with a rate of 75 

 liters per minute (the usual rate of ventilation) as was the U tube in 

 removing carbon dioxide from the air current with a rate of 2 liters 

 per minute. After a number of experiments an absorber was devised 

 which in its present form is shown in figure 1 2 and in cross-section in 

 figure 13. 



DESCRIPTION OP THE CARBON-DIOXIDE ABSORBERS. 



The absorbers are constructed of seamless drawn brass tubing 150 

 mm. internal diameter, 380 mm. long, and with walls 1.5 mm. thick. 

 One end consists of a brass disk to which a 64 mm. length of brass tube 

 is permanently soldered and the joints stiffened by being well banked 

 with solder. The other end is detachable and consists of a similar brass 

 disk somewhat larger in diameter (157 mm.), which can be drawn up 

 against a rubber gasket fitting against the face of a shoulder on the end 

 of the main tube, so that by means of the large collar C (fig. 13) the 

 opening can be tightly closed. All parts are heavily plated internally 

 and externally with silver, which has been found to stand the action of 

 the soda lime indefinitely. For convenience each can is lettered with 

 blue enamel. 



