LOW-TEMPERATURE RESEARCHES 



vented very soon its particles will again have power 

 to kick themselves apart and resume the gaseous state. 

 Something, then, must be done to insulate the liquefied 

 gas, else it will retain the liquid state for too short a 

 time to be much experimented with. How might such 

 insulation be accomplished ? 



The most successful attack upon this important 

 problem has been made by Professor Dewar. He in- 

 vented a receptacle for holding liquefied gases which, 

 while not fulfilling the ideal conditions referred to 

 above, yet accomplishes a very remarkable degree of 

 heat insulation. In consists of a glass vessel with 

 double walls, the space between which is rendered a 

 vacuum of the highest practicable degree. This vacu- 

 um, containing practically no particles of matter, can- 

 not, of course, convey heat-impulses to or from the 

 matter in the receptacle with any degree of rapidity. 

 Thus one of the two possible means of heat transfer is 

 shut off and a degree of insulation afforded the lique- 

 fied substance. But of course the other channel, ether 

 radiation, remains. Even this may be blocked to a 

 large extent, however, by leaving a trace of mercury 

 vapor in the vacuum space, which will be deposited 

 as a fine mirror on the inner surface of the chamber. 

 This mirror serves as an admirable reflector of the 

 heat-rays that traverse the vacuum, sending more than 

 half of them back again. So, by the combined action 

 of vacuum and mirror, the amount of heat that can 

 penetrate to the interior of the receptacle is reduced 

 to about one-thirtieth of what would enter an ordinary 

 vessel. In other words, a quantity of liquefied gas 

 which would evaporate in one minute from an ordinary 



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