12 ATTAINMENT OF VERY LOW TEMPERATURES. 



of wide rubber tube. The side tube d communicated by means of a 

 flexible rubber tube with a small gasometer. 



The vacuum vessel rested on the point at which it was finally sealed 

 (fig. 2, B), so that when the liquid air cock was opened by rotating the 



A B 



Fig. 2. — Apparatus for measuring air lost by evaporation of liquid. 



thumb screw /, it merely turned on its axis. The quantity of gaseous 

 air produced by the evaporation of the liquid air could be measured 

 by measuring the rise of the gasometer attached to d. The quantity 

 of liquid air collected in the vacuum vessel amounted to about one 

 kilogram per hour ; the loss by evaporation corresponding to the same 

 period was usually seventy to eighty grams per hour. 



The quantity of heat entering the Hampson apparatus through its 

 insulating packing of animal wool was determined by stopping the com- 

 pressor when the liquid air in the collecting chamber had been allowed 

 to accumulate for five minutes, closing the expansion valve, allowing 

 the air to escape from the regenerator coil by means of a side-cock but- 

 side the apparatus, and measuring the rate of evaporation of the liquid 

 air from the inside of the apparatus, and the rate of change of tem- 

 perature of the regenerator coil. The latter measurement was made 

 by means of an air thermometer with a narrow C3dindrical bulb which 

 was inserted through the center of the coil in place of the valve spindle. 

 The following is a record of the results of an experiment. 



