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102 Professors W. B. and R. BE. Rogers 
The stop-cock at the bottom of the measuring tube is used for 
adjusting the level of the mercury in the two limbs at the be- 
ginning of each experiment, and for removing the mercury which 
is poured in through the funnel above, to maintain the columns 
at the same height during the progress of the absorption. 
It will be seen from the figure, that while the flask and meas- 
uring tube are both constantly immersed as the experiment is 
going on, and are thus kept at an invariable temperature, the 
connecting tube, between the two levels of water, is necessarily 
out of the liquid, and must be influenced by the temperature o 
the ambient air. ‘The capacity of this exposed part of the tube 
was found to be very nearly 2,ths of a cubic inch, the expansion 
of which for 1° is equal to 5,4,; cubic inch. As the tempera- 
ture of the apartment seldom differed from that of the apparatus 
by more than some four or five degrees during our experiments, 
the entire error would be within -4,th of an inch, while as be- 
fore mentioned, the smallest reliable reading of the measuring 
scale is ;4,th cubic inch. It has therefore been thought useless 
200 
to attempt any correction for the temperature of this part of the 
enclosed gas. 
Mode of Manipulating —From the description just given of 
the several parts of the apparatus, the general method of opera- 
ting with it will be readily inferred, and but few words need be 
added on this head. 
Bringing the entire apparatus to the required temperature, (60° 
in most of our experiments,) the unit bottle, charged with the 
liquid to be used, is hung in the large reservoir, to attain exactly 
the same temperature. ‘The back of the gasometer pipe is in-| 
serted in the flask air-tight, and a brisk stream of carbonic acid 
is suffered to flow through the apparatus for five minutes. Some 
mercury is now poured by a long funnel into the measuring tube 
to arrest the current. The flask being raised so as to lay bare 
the mouth, the cork is withdrawn, and at the same moment, 
while the stream of gas is pouring out and overflowing from the 
flask, the unit bottle is secured in the opening and fastened by 
the spring above. After swinging the flask down to its vertical 
position, the level of the mercury in the measuring tube is care- 
fully adjusted, and the agitation is now commenced. The liquid 
at first descends only by drops, but soon begins to flow more rap- 
idly. ‘The vibratory movement of the flask is of that sudden 
kind which effectually brings the gas and liquid into intricate 
contact—and the absorption rapidly proceeds. Two operators 
are necessary in conducting the experiment, one to keep up the 
shaking, and the other to supply the outer limb of the measuring 
tube with mereury as the column on the other side ascends. 
With water, we have found the absorption to be completed in 
about five minutes. The oils, dense saline solutions and sul- 
