18S THE ROYAL SOCIETY OF CANADA 



by evaporated air being drawn off by the vacuum pump, and Li is 

 partially immersed in a bath of liquid air contained in the flask M. 

 The valve A serves to admit more liquid air from the reserve flasks 

 whenever the indicator Ei of the cork float E shows that it is required. 

 The expansion or chief regenerator coil is well wrapped in flannel and 

 still further protected by the double walled silvered vacuum flask M^. 

 The liquid, as it is formed, passes through the opening in the bottom 

 of the flask Mo and is collected in the silvered flask Mz. The float 

 indicator D, Di, D^ serves to show the level of the liquid in this collecting 

 flask. The weight D is connected with the thin German silver float 

 Di by means of a silk thread running over three pulleys D2 each with 

 jewel mountings. Two valves, B and J5i, are used for drawing off the 

 liquid. These valves are so arranged that they may be pre-cooled 

 by the cold gaseous hydrogen that may be returned to the gasometer. 

 The stuffing boxes and screw thread for the valves B, Bi, C and A are 

 so arranged that they are not exposed to cooling and thus the danger 

 of freezing is eliminated. 



The insulation of the apparatus has been carefully studied. 

 Vacuum flasks are used where possible and wherever parts are cooled 

 below the temperature of liquid air, they are surrounded by an atmo- 

 sphere of hydrogen or by a partial vacuum, in order to avoid un- 

 necessary condensation. The regenerator coils are wrapped in flannel 

 and fit snugly in German silver containers so as to insure a proper 

 exchange of heat between the incoming and outgoing gases. All 

 parts as far as possible are constructed of German silver, because of 

 its low coefficient of thermal conductivity. The entire apparatus is 

 packed in natural wool and enclosed in a thin brass case that is 

 sealed except for the drying tubes H and Hi. These tubes serve to 

 prevent water vapour from condensing and collecting inside. Fig. 4 

 shows plainly the arrangement for supporting the apparatus, together 

 with the scheme of the pipe connections. Mercury traps / and Ji 

 serve to protect the apparatus at all times from any excess of pressure, 

 while rubber safety valves G and d serve to accommodate any sudden 

 or violent increase in pressure. 



When it is required to operate the cycle the complete system of 

 piping, etc., is thoroughly exhausted. It is then filled with hydrogen 

 and again exhausted, the operation being repeated until the hydrogen 

 in the system is absolutely pure. The refrigerator surrounding the 

 coil Li is then filled with liquid air and the pre-cooling is effected by 

 allowing the hydrogen to stream through at low pressure for some 

 time. When the thermocouples indicate that the temperature of the 

 hydrogen at the expansion valve is — 205°C., the valve is gradually 



