The purifying apparatus for the air-current is compactly and
conveniently placed on a solidly constructed table which can be moved
about the laboratory at will. The special form of caster on the bottom
of the posts of the table permits its movement about the laboratory at
will and by screwing down the hand screws the table can be firmly fixed
to the floor.
The details of the table are shown in fig. 30. (See also fig. 4, page
4.) The air coming from the calorimeter passes in the direction of the
downward arrow through a 3/4-inch pipe into the blower, which is
immersed in oil in an iron box F. The blower is driven by an electric
motor fastened to a small shelf at the left of the table. The air
leaving the blower ascends in the direction of the arrow to the valve
system H, where it can be directed into one of the two parallel sets of
purifiers; after it passes through these purifiers (sulphuric-acid
vessel 2, potash-lime container K, and sulphuric-acid vessel 1) it goes
through the sodium-bicarbonate can G to a duplicate valve system on top
of the table. From there it passes through a pipe along the top of the
table and rises in the vertical pipe to the hose connection which is
coupled with the calorimeter chamber.
The electric motor is provided with a snap-switch on one of the posts of
the table and a regulating rheostat which permits variations in the
speed of the motor and consequently in the ventilation produced by the
blower. The blower is well oiled, and as oil is gradually carried in
with the air, a small pet-cock at the bottom of the T following the
blower allows any accumulated oil to be drawn away from time to time.
The air entering the valve system at H enters through a cross, two arms
of which connect with two "white star" valves. The upper part of the
cross is connected to a small rubber tubing and to the mercury
manometer D, which also serves as a valve for passing a given amount of
air through a series of U-tubes for analysis of the air from time to
time. It is assumed that the air drawn at the point H is of
substantially the same composition as that inside the chamber, an
assumption that may not be strictly true, but doubtless the sample thus
obtained is constantly proportional to the average composition, which
fluctuates but slowly. Ordinarily the piping leading from the left-hand
arm of the tube D is left open to the air and consequently the
difference in the level of the mercury in the two arms of D indicates
the pressure on the system. This is ordinarily not far from 40 to 50
millimeters of mercury.
[Illustration: FIG. 30.--Diagram of absorber table. 1 and 2 contain
sulphuric acid; K contains potash-lime; G, sodium bicarbonate can; F,
rotary blower for maintaining air-current; H, valves for closing either
side; and D, mercury manometer and valve for diverting air to U-tubes on
table. Air leaves A, passes through the meter, and then through drying
tower B and through C to ingoing air-pipe. At the left is the regulating
rheostat and motor and snap-switch. General direction of ventilation is
indicated by arrows.]
The absorber table, with the U-tubes and meter for residual analyses, is
shown in the foreground in fig. 2. The two white porcelain vessels with
a silver-plated can between them are on the middle shelf. The sodium
bicarbonate can, for removing traces of acid fumes, is connected in an
upright position, while the motor, the controlling rheostat, and the
blower are supported by the legs near the floor. The two rubber pipes
leading from the table can be used to connect the apparatus either with
the bed or chair calorimeter. In fig. 4 the apparatus is shown connected
with the bed calorimeter, but just above the lowest point of the rubber
tubing can be seen in the rear the coupling for one of the pipes leading
from the chair calorimeter. The other is immediately below and to the
left of it.