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_. * * * * * METHOD OF PRODUCING ALCOHOL.