26 COMPARISONS OF RESPIRATORY EXCHANGE. 



Air-drier. — The air-current coming from the blower brings with it 

 the water-vapor from the air-moistener and a certain amount of water- 

 vapor from the lungs of the subject. The method used in this apparatus 

 of determining the carbon-dioxide production by weight necessitates 

 the removal of water-vapor from the air-current before it reaches the 

 carbon-dioxide absorbers, as any water-vapor reaching the soda-lime 

 would be absorbed in the latter. The water-absorbers or air-driers 

 used in this apparatus are two 4-liter Wolff bottles connected in series 

 and containing sulphuric acid. These bottles are fitted with glass tubes 

 of about the same diameter as the piping of the apparatus, the entrance 

 tubes dipping about 2 cm. into the acid. The usual method of use is 

 to fill the first bottle to a certain level, and when sufficient water has 

 been absorbed to increase the level of the liquid to a point determined 

 by experience, the absorber is removed. If this routine is strictly fol- 

 lowed, the second bottle never has to be replaced, these two absorbers 

 being sufficient to remove all of the water- vapor from the air-current. 

 In the earlier experimenting with this apparatus, the first bottle was 

 filled with pumice stone and sulphuric acid added to half the height 

 of the vessel. The second bottle was half filled with pumice stone, and 

 acid then added to a one-third level. Later, instead of using pumice 

 stone in the bottles, they were simply filled about two-thirds full 

 with sulphuric acid, the entrance tubes dipping into the acid. 



The glass tubes leading into and out of the Wolff bottles were made 

 especially high for two reasons : First, if there were a slight back suction 

 the acid would rise in the inlet tube so that considerable pressure would 

 have to be overcome with this length of tube before the acid could 

 travel back into the blower; second, the length of the exit tube enabled 

 any sulphuric acid mechanically carried forward to drain back into the 

 Wolff bottle. This mechanical carrying forward has more recently 

 been prevented by the use of a special bulb with a perforated trap 

 inside, which serves to catch the acid more efficiently and allows it to 

 drain back into the bottle. 



Carbon-dioxide absorbers. — The carbon-dioxide absorbers employed 

 during the first two years after the apparatus was developed were 

 constructed on the same principle as those used for the respiration calo- 

 rimeter. 1 They were made of brass tubing, which was silver-plated to 

 resist the action of alkali. Their length was 26 cm. and their diameter 

 12 cm. A hose-coupling of standard size was soldered at each end for 

 connecting with the rest of the apparatus. As the head of the can was 

 removable, it could be easily filled. When the can was filled with 

 granulated soda-lime of the size of half a pea, 60 gm. of carbon dioxide 

 could be absorbed without allowing any to pass, with the circulating 

 air moving at the rate of 35 liters per minute. 



M3ee K, fig. 1, p. 15. 



