3°8 
Journal of Agricultural Research 
Vol. V, No. 8 
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 0.1 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 
