To absorb 25 to 40 grams of water-vapor in an hour from a current of air
moving at the rate of 75 liters per minute and leaving the air
essentially dry under these conditions has been met by the apparatus
herewith described. The earlier attempts to secure this result involved
the use of enameled-iron soup-stock pots, fitted with special
enameled-iron covers and closed with rubber gaskets. For the preliminary
experimenting and for a few experiments with man these proved
satisfactory, but in spite of their resistance to the action of
sulphuric acid, it was found that they were not as desirable as they
should be for continued experimenting from year to year. Recourse was
then had to a special form of chemical pottery, glazed, and a type that
usually gives excellent satisfaction in manufacturing concerns was used.
This special form of absorbers presented many difficulties in
construction, but the mechanical difficulties were overcome by the
potter's skill and a number of such vessels were furnished by the
Charles Graham Chemical Pottery Works. Here again these vessels served
our purpose for several months, but unfortunately the glaze used did not
suffice to cover them completely and there was a slight, though
persistent, leakage of sulphuric acid through the porous walls. To
overcome this difficulty the interior of the vessels was coated with hot
paraffin after a long-continued washing to remove the acid and after
they had been allowed to dry thoroughly. The paraffin-treated absorbers
continued to give satisfaction, but it was soon seen that for permanent
use something more satisfactory must be had. After innumerable trials
with glazed vessels of different kinds of pottery and glass,
arrangements were made with the Royal Berlin Porcelain Works to mold and
make these absorbers out of their highly resistant porcelain. The result
thus far leaves nothing to be desired as a vessel for this purpose. A
number of such absorbers were made and have been constantly used for a
year and are absolutely without criticism.
Fig. 28 shows the nature of the interior of the apparatus. The air
enters through one opening at the top, passes down through a bent pipe,
and enters a series of roses, consisting of inverted circular saucers
with holes in the rims. The position of the holes is such that when the
vessel is one-fourth to one-third full of sulphuric acid the air must
pass through the acid three times. To prevent spattering, a small
cup-shaped arrangement, provided with holes, is attached to the opening
through which the air passes out of the absorber, and for filling the
vessel with acid a small opening is made near one edge. The
specifications required that the apparatus should be made absolutely
air-tight to pressures of over 1 meter of water, and that there is no
porosity in these vessels under these conditions is shown by the fact
that such a pressure is held indefinitely. The inside and outside are
both heavily glazed. There is no apparent action of sulphuric acid on
the vessels and the slight increase in temperature resulting from the
absorption of water-vapor as the air passes through does not appear to
have any deleterious effect.
[Illustration: FIG. 28.--Cross-section of sulphuric-acid absorber. The
air enters at the top of the right-hand opening, descends to the bottom
of the absorber, and then passes through three concentric rings, which
are covered with acid, and it finally passes out at the left-hand
opening. Beneath the left-hand opening is a cup arrangement for
preventing the acid being carried mechanically out through the opening.
The opening for filling and emptying the absorber is shown midway
between the two large openings.]
The vessels without filling and without rubber elbows weigh 11.5
kilograms; with the special elbows and couplings attached so as to
enable them to be connected with the ventilating air-system, the empty
absorbers weigh 13.4 kilograms; and filled with sulphuric acid they
weigh 19 kilograms. Repeated tests have shown that 5.5 kilograms of
sulphuric acid will remove the water-vapor from a current of air passing
through the absorbers at the rate of 75 liters of air per minute,
without letting any appreciable amount pass by until 500 grams of water
have been absorbed. At this degree of saturation a small persistent
amount of moisture escapes absorption in the acid and consequently a
second absorber will begin to gain in weight. Experiments demonstrate
that the first vessel can gain 1,500 grams of water before the second
gains 5 grams. As a matter of fact, it has been found more advantageous
to use but one absorber and have it refilled as soon as it has gained
400 grams, thus allowing a liberal factor of safety and no danger of
loss of water.