3o8 Journal of Agricultural Research voi, v.no.s 



cient enough for further use, which is shown by its change in color. 

 The fresh, somewhat moist soda lime is a dingy white, but in use it 

 becomes much lighter and clearer, owing to both the absorption of carbon 

 dioxid and the loss of moisture, which is taken from the soda lime by 

 the dry air. The bottle may be recharged whenever all of the visible 

 surface of soda lime has thus changed, though if the whitened material 

 has not become compacted into a hard mass which will prevent air from 

 passing through it the efficiency of the soda lime may be restored by 

 passing air containing water vapor through the bottle until the dry 

 material has absorbed about as much moisture as it contained originally, 

 as may be judged from the darkening of the color. In this manner a 

 given charge may be used at least twice. In either case, if the bottle is 

 opened, any soda lime not compacted but still remaining granular may 

 be used again, especially if it is mixed with a large proportion of fresh 

 material. In an ordinary rest experiment in which carbon dioxid is 

 removed from the air current at a rate of 25 to 30 gm. an hour, the mate- 

 rial in one of these bottles will absorb at least 150 to 200 gm. of carbon 

 dioxid before all the soda lime has whitened. 



These bottles are quite"satisfactory in many respects, but in using them 

 great care is necessary to avoid leakage of air between the stopper and 

 the neck of the bottle, or between the stopper and the tubes passing 

 through it, especially after the bottle has been in use a short time. When 

 these joints are made, they are thoroughly painted with shellac, but 

 since the stopper is quite flexible there is possibility of breaking the coat- 

 ing in using the bottle. Some of these chances for leakage will be elimi- 

 nated by a special cover designed to be clamped to the top of the bottle, 

 into which the inlet and outlet tubes are soldered. 



The soda lime is used moist rather than dry because it is more efficient 

 in that condition. In passing through this moist material the dry air 

 from the water-vapor absorber takes moisture from it. The air from the 

 carbon-dioxid absorber is therefore passed through another bottle of 

 sulphuric acid, to catch the moisture given off by the soda lime. This 

 bottle is weighed with the two soda-lime bottles to find the amount of 

 carbon dioxid removed from the air current coming from the respiration 

 chamber, the three bottles standing together on the pan of the large 

 balance being weighed as a unit. Their total weight, which is less than 

 12 kgm., is ascertained accurately to o.i gm. 



Trap for Atomized Sulphuric Acid 



Though the pumice in the stopper of the sulphuric-acid bottle effectively 

 arrests visible particles spattered up by the vigorous agitation of the acid 

 or blown up in the air current, acid in some condition, apparently re- 

 sembling vaporous exhalation, escapes in the air leaving the bottle. The 

 amount of acid that leaves the absorber is so small that even after the air 



