Q2 STORRS AGRICULTURAL EXPERIMENT STATION. 
air current by cooling to about —17° centigrade leaves a small 
and reasonably uniform amount of moisture and thus greatly 
facilitates the determination of the latter in the samples 
analyzed. Four U tubes are used for the absorbing, two for 
the carbon dioxide and two for the water of each sample. 
These tubes are connected in series and conveniently supported 
in a nearly horizontal position while the air is passing through. 
For weighing they are separated and hung by loops of plati- 
num or aluminum wire in the balance. 
freezing Apparatus.—In our experience during the several 
years in which the apparatus and experimental methods here 
used have been in process of elaboration it has been found 
very desirable to have the air enter the respiration chamber as 
dry as possible. It was with this fact in view that the plan 
was first adopted for freezing the air as it came from outside 
before it entered the chamber. The freezer used for this pur- 
pose consisted practically of two large U tubes of copper. 
These are connected with each other and with the pipe through 
which flows the current of incoming air. They stand upright 
in a wooden box which is kept filled with a freezing mixture 
of salt and ice. In this way the current of air has to pass 
through nearly 12 ft. of copper tubing which is covered by the 
freezing mixture. This method of removing the excess of 
moisture from the air before it enters the chamber proved so 
satisfactory as to lead to its adoption in quantitative determi- 
nations of the moisture in the outgoing air. For this purpose, 
however, a somewhat more complicated freezer is necessitated 
by the fact that the water which it collects must be accurately 
weighed. 
The use of ice and salt for freezing proved unsatisfactory 
because of the trouble of frequent renewal, the expense for 
material and labor, which was not inconsiderable, the difficulty 
of getting a satisfactory low temperature and especially the 
impossibility of maintaining a constant temperature. For the 
later experiments we have adopted the plan of immersing the 
freezers in a brine cooled by the expansion of ammonia gas. 
For a cooling apparatus we have found the so-called ‘‘ Eco- 
nomical Ice Machine’’ made by the Atlantic Refrigerating 
Company, of Springfield, Mass., simple, easily operated, and 
entirely efficient for the purpose. 

