618 THE POPULAR SCIENCE MONTHLY. 



these two chemists, commencing with those of Cailletet. Our en- 

 graving (Fig. 1) shows the great apparatus constructed by M. Cail- 

 letet in his shops at Chatillon-sur-Seine. It consists of a hollow cylin- 

 der 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 com- 

 pressed, it is poured into the glass cup (r, 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 ter- 

 minates in a small wheel with handle-pins, 0. 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 per- 

 manent. 



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 lique- 

 fied. Thus this capillary tube can be surrounded with freezing mixt- 

 ures, 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 exami- 

 nation, 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. 



A r is a modified Thomasset manometer, verified by means of an 



