The "cryogen," a new apparatus constructed by Mr. E. Ducretet, from
instructions given by Mr. Cailletet, is designed for effecting a fall of
temperature of from 70° to 80° C. below zero, through the expansion of
liquid carbonic acid.
The apparatus consists of two concentric vessels having an annular space
between them of a few centimeters. A worm, S, is placed in the internal
vessel R. All this is of nickel plated copper. The worm, S carries, at
Ro', an expansion cock and ends, at O in the annular space, R'. A very
strong tube is fixed to the cock, Ro', and to the ajutage, A'. It
receives the tube, Tu, which, at the time of an experiment, is coupled
with the cylinder of carbonic acid, CO². A tubulure, D, usually closed
by a plug, Bo, communicates with the inner receptacle, R. This is
capable of serving in certain experiments in condensation. The table,
Ta, of the tripod receives the various vessels or bottles for the
condensed products.
The entire apparatus is placed in a box, B, lined with silk waste and
provided with a cover, C, of the same structure. Apertures, Th, Ro, and
T", allow of the passage of a key for acting upon the cock, Ro', as well
as of thermometers and stirrers if they are necessary.
When it is desired to operate, the internal vessel, R, is filled with
alcohol (3 quarts for the ordinary model). This serves as a refrigerant
bath for the experiments to be made. The worm, S, having been put in
communication with the carbonic acid cylinder, CO², the cock, Ro, of the
latter is turned full on. The cock of the worm, which is closed, is
opened slightly. The vaporization and expansion of the liquid carbonic
acid cause it to congeal in the form of snow, which distributes itself
and circulates in the worm, S, and then in R. The flakes thus coming in
contact with the metallic sides of S rapidly return to the gaseous state
and produce an energetic refrigeration. At the lower part of the annular
space, R', are placed fragments of sponge impregnated with alcohol. The
snow that has traversed the worm without vaporizing reaches R'. and
dissolves in this alcohol, and the refrigeration that results therefrom
completes the lowering of the temperature. The gas finally escapes at O,
and then through the bent tube, T".
[Illustration: CAILLETET'S CRYOGEN.]
The apparatus may be constructed with an inverse circulation, the
carbonic acid then entering the annular vessel, R, directly, and
afterward the worm, S, whence it escapes to the exterior of the
apparatus. The expansion cock sometimes becomes obstructed by the
solidification of the snow. It will then suffice to wait until the
circulation becomes re-established of itself. It may be brought about by
giving the cock, Ro', a few turns with the wooden handled key that
serves to maneuver the latter. It is not necessary to have a large
discharge of carbonic acid, and consequently the expansion cock needs to
be opened but a little bit. A few minutes suffice to reduce the
temperature of the alcohol bath to 70°, with an output of about from 4½
to 5½ lb. of liquid carbonic acid. When the circulation is arrested, the
apparatus thus surrounded by its isolating protective jackets becomes
heated again with extreme slowness. In one experiment, it was observed
that at the end of nine hours the temperature of the alcohol had risen
but from 70° to 22°. On injecting a very small quantity of liquid
carbonic acid from time to time, a sensibly constant and extremely low
temperature may be maintained indefinitely.--_Le Genie Civil_.
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