816 



Professor Dewar 



[April 1, 



experiment may be observed. This was generally from 2 J to 3 cubic 

 feet. If there is a very small proportion of some substance not 

 liquefiable or soluble in liquid air, then we should expect the vessel 

 B would not fill up completely into the capillary tube. This is, 

 however, exactly what does take place. After 40 minutes' cooling, 



Fig. 1. 



the vessel B and the cool part of the tube were filled with liquid. 

 In this experiment some 80 litres of air were condensed, and any 

 accumulated uncondensed matter must have been concentrated in the 

 upper part of the capillary tube, which had a volume of * 5 c.c. 

 Under the conditions, therefore, the material looked for must be 

 less than 1 part by volume in 180,000 of air.* 



* These experiments, alono; with the succeeding ones on Bath Gas, were 

 all described in a Paper entitled, ' Liquefaction of Air and the Detection of 

 Impurities,' given at the Chemical Society on 4th November, 1807. 



