juiy 3 i,i<>i6 Respiration Calorimeter 707 



which is shown in Plate XCII, has also proved quite satisfactory. A 

 charge of 500 c. c. of sulphuric acid in either of these bottles will continue 

 for several hours to remove all water vapor from air passing through at 

 any rate maintained in the experiments thus far conducted with the 

 apparatus, even though in some cases water vapor in the air is near the 

 saturation point. The bottle and the acid weigh less than 2 kgm., and 

 by means of a sensitive balance of 10 kgm. capacity the change in 

 weight during a given period is ascertained to an accuracy of 0.05 gm. 



Carbon dioxid is removed from the air which leaves the acid bottle 

 by soda-lime in a large-sized U-tube of special design (PI. XCII). Each 

 arm of the U consists of glass tubing 23 cm. long and 75 mm. in diameter, 

 and the two are joined at the bottom by glass tubing of 15-mm. bore bent 

 in a semicircle, leaving a narrow space between them. The upper end 

 of each arm of the U-tube is closed by a ground-glass stopper from the 

 top of which projects a glass tube of 10-mm. bore bent at right angles. 

 The bottom of the stopper is closed except for an aperture of 10 mm., 

 and in the space within the stopper is cotton wool to prevent particles 

 of soda-lime from leaving the tube in the outgoing air. 



A piece of fine-mesh brass wire gauze is put on the bottom of each large 

 tube to keep the bent portion empty, and each arm is then filled to the 

 stopper with soda-lime in particles of about the size of a dried pea, ap- 

 proximately 2 kgm. of soda-lime being required to fill both arms. This 

 amount of material when fresh will commonly absorb at least 100 gm. of 

 carbon dioxid before it needs attention, which is indicated by the color of 

 the soda-lime. The gray-colored material, which is somewhat moist in 

 the fresh condition, becomes white with use, owing to both loss of moist- 

 ure and absorption of carbon dioxid. When the moisture is entirely gone 

 the efficiency of the soda-lime is low; but by passing moist air through the 

 tube it may be restored to such an extent that the soda-lime may be used 

 for at least one more period. 



To catch the moisture given up by the soda-lime to the dry air coming 

 from the first water absorber, the air leaving the U-tube is passed through 

 another bottle of acid. Both the acid bottle and the U-tube, for which 

 there is easily room on the pan of the balance by which the gain in weight 

 of the absorbers is determined, are weighed together to find the quantity 

 of carbon dioxid removed from the circulation of air. Their total weight 

 is less than 5 kgm., and their change in weight is ascertained to an accu- 

 racy of 0.05 gm. 



The air leaving the second acid bottle is passed through a trap of cotton 

 wool (PI. XCIII) to catch any spray that might be carried from the 

 sulphuric acid by the moving air. The quantity of acid that leaves the 

 absorber is so small that the trap need not be weighed. 



