Dewar's Method of producing High Vacua. 

 Fijr. 1. 



499 



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from the beginning o£ the experiment. The amount of liquid 

 air used in the course of the exhaustion was determined by 

 weighing the flask in which it was stored at the commence- 

 ment and conclusion. Two distinct experiments with the 

 charcoal receptacle already described gave 340 grams and 

 295 grams as the amount of liquid air evaporated in exhaust- 

 ing a five-inch bulb. About 800 grams of liquid air were 

 required to cover the charcoal absorber, which was placed in 

 a cylindrical Dewar's vessel 40 centimetres in diameter. 



§ 5. Another experiment with a larger absorber, of 550 c.c. 

 capacity, containing 246 grams of charcoal, gave penetrating- 

 X-rays after the charcoal had been cooled for an hour and a 



2 M2 



