* * * * *

MR. CAILLETET’S CRYOGEN.

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 deg. to 80 deg.  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, CO squared.  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, CO squared, 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