Page:Popular Science Monthly Volume 12.djvu/636

618 these two chemists, commencing with those of Cailletet. Our engraving (Fig. 1) shows the great apparatus constructed by M. Cailletet in his shops at Châtillon-sur-Seine. It consists of a hollow cylinder of steel, A, firmly secured on a bed of cast-iron by means of the clamps B B. A cylindrical rod of untempered steel, serving as a plunger-piston, enters this cylinder, which must be filled with water. The opposite extremity of the rod terminates in a square-threaded screw, passing through the bronze nut F attached to the wheel M. According to the direction given to the wheel by means of the pins at its circumference, the plunger-piston may be made to advance or retreat in the axis of the pump-barrel. A packing of leather prevents the compressed liquid from escaping from the cylinder.

In introducing the water, or other liquid designed to be compressed, it is poured into the glass cup G, which communicates with the inside of the apparatus. A steel screw, with conical point, closes the narrow passage through which the liquid enters. This screw terminates in a small wheel with handle-pins, O. By this arrangement we can suddenly release the compressed gases, and see a dense mist form in the capillary glass tube containing them. (This tube is seen in the middle of the cylinder m.) The mist is formed under the influence of the external cold produced by the sudden removal of pressure, and it is an infallible sign of the liquefaction, or even the congelation, of the gases which hitherto have been regarded as permanent.

a is a steel reservoir, capable of bearing a pressure of 900 or even 1,000 atmospheres; it is connected with the compression-apparatus by a capillary tube of metal. The water in the cylinder, under the pressure of the piston, enters this reservoir, and acts on mercury which compresses the gas.

b is the ajutage which receives the glass apparatus designed to hold the gas under experiment; it is connected with the top of the reservoir by a nut. Fig. 2 represents the arrangement of this part, half the actual size.

m is a flint-glass cylinder, inclosing another glass cylinder, in the middle of which is seen the fine tube in which the gas is to be liquefied. Thus this capillary tube can be surrounded with freezing mixtures, or with liquid protoxide of nitrogen. The outer cylinder m, which is concentric with the inner one, and contains substances which have a strong affinity for moisture, prevents the deposit of ice or vapor on the cooled tube, which would hinder observation.

p is a cast-iron stand to hold the reservoir a. Screws d d serve to raise or lower the reservoir for the purpose of spectroscopic examination, or of projecting the experiments on a screen.

An ajutage S connects together the metallic capillary tubes which transmit the pressure to the various portions of the apparatus.

N is a modified Thomasset manometer, verified by means of an