io8 
Journal of Agricultural Research 
Vol. XXIII, No. 3 
respiration tubes; a short interval, during which the barometer may be 
read, is allowed for complete absorption; and the manometers are again 
gently tapped and read. 
From the manometer and barometer readings, the temperature used 
in the experiment, and the net volumes of the apparatuses, 4 * corrected 
for the volumes of the respiring material and of the caustic which was 
admitted, and for the changed positions of the mercury in the ma¬ 
nometers, 1 the three significant volumes of air under standard conditions 
(o° C. at 760-mm. pressure) can be computed. From these three volumes 
the volume of oxygen jabsorbed, the volume of C 0 2 given off, and the res¬ 
piratory quotient 
are easily derived. 
If extreme accuracy is desired, C 0 2 -free air may be introduced at the 
beginning 6 and further corrections may be introduced for the fact 
that the period for C 0 2 production, from the putting of the apparatuses 
together to the making of the second manometer reading, is slightly 
longer than that for oxygen consumption, from the closing of the stop¬ 
cocks to the time of the second manometer reading, and for the further 
fact that the volume determined for C 0 2 respired includes also oxygen 
absorbed during the very short interval between making the first and 
second manometer readings. 
Since the volume of oxygen absorbed is usually greater than that of 
C 0 3 given off, the reduction of pressure thus brought about in the 
respirometer starts the flow of caustic when the stopcock is opened, and 
the absorption of C 0 2 also aids in the introduction of the caustic. It is 
sometimes necessary, however, to force the last of the caustic down by 
gently blowing into the caustic chamber through a rubber tube slipped 
over its top. 
The caustic, running down the side of the respirometer its entire length 
and over the top of the seed container, insures rapid absorption of the 
C 0 2 . Meantime, the roof of the seed container and the edge which pro¬ 
trudes below its perforated plate protects the seeds completely from 
contact with the caustic. 
After a complete determination the battery of respirometers is removed 
from the water bath, stopcocks are opened, the mercury seals are removed 
by suction into a suction flask used as a trap, and the apparatuses are 
taken apart, emptied, and washed with a dilute acid and then with water. 
The seed containers may be washed by pouring acid over them without 
disturbing the seeds, and then both seeds and containers may be further 
washed under a stream of water by inserting them into Gooch crucibles 
in such a manner that the open sides of the containers are closed against 
the sides of the crucibles and the loss of seeds thus prevented. 
The containers and seeds are now ready to be returned to the cleaned 
respirometers for another period of respiration. 
4 The net air capacity of each apparatus with the seed container in place is determined from the weight 
of the water it takes to fill it and is corrected for each experiment by subtracting the volumes of the 
respiring material. 
6 If the bore of the manometer tube is just 2 mm., a change of 3.185 mm. in the height of the mercury on 
the side toward the respiration chamber—that is, a difference of 6.37 ram. in the height of the mercury in 
the two arms of the manometer—corresponds to a change of 0.01 c. c. in the uncorrected volume of the air 
in the apparatus. 
6 The CO2 in normal air would make a difference of only 0.2 mm. on the manometer, which is not much 
above the limit of error in adjustment and reading, and would, under the method adopted, affect the values 
for oxygen consumption and CO2 production alike. It is believed that leaving a vessel of strong caustic 
solution exposed to the air for a few hours near where the apparatus is to be set up, and then aerating the 
apparatus and respiring material with air drawn from the open room over this caustic solution, reduces 
the error from atmospheric CO2 well below the lowest possible limits of error. This is the procedure 
adopted in the work reported in the following article. 
