_Mode of Measuring the Gases and Absorption_.--The tube that
communicates with the vessel, F, is put in communication, after the
latter has been completely filled with water, with the point of the
cock, _b_ (Fig. 2). Then the latter is opened, as is also the pinch cock
on the rubber tubing, and water is allowed to enter the burette through
the bottom until the level is at the zero of the graduation. There are
then 100 cubic centimeters in the burette. The superfluous gas has
escaped through the cock, _a_, and passed through the water in the
funnel. The cock, _a_, is afterward closed by turning it 90 deg.. To
cause the absorbing liquid to pass into the burette, the water in the
graduated cylinder is made to flow by connecting the rubber tube, s, of
the bottle, S, with the point of the burette. The cock is opened, and
suction is effected with the mouth of the tube, r. When the water has
flowed out to nearly the last drop, _b_ is closed and the suction bottle
is removed. The absorbing liquid (caustic potassa or pyrogallate of
potassa) is poured into a porcelain capsule, P, and the point of the
burette is dipped into the liquid. If the cock, _b_, be opened, the
absorbing liquid will be sucked into the burette. In order to hasten
the absorption, the cock, _b_, is closed, and the burette is shaken
horizontally, the aperture of the funnel being closed by the hand during
the operation.

If not enough absorbing liquid has entered, there may be sucked into the
burette, by the process described above, a new quantity of liquid. The
reaction finished, the graduated cylinder is put in communication with
the funnel by turning the cock, _a_. The water is allowed to run from
the funnel, and the latter is filled again with water up to the mark.
The gas is then again under the same pressure as at the beginning.

After the level has become constant, the quantity of gas remaining is