1914] on The Coming of Age of the Vacuum Flask 



241 



insulation purposes, the convective transference of heat being stopped. 

 If, however, the inner vessels were coated with a bright metallic deposit 

 then the radiation influx is very greatly diminished. This is readily 

 shown by making a half -silvered vessel. The radiation from the 

 silvered and the clear sides respectively is compared by presenting 

 each in turn to a thermopile connected to a galvanometer, whose 

 indications are shown by a moving spot of light on the screen. Two 



Dry Air 

 Isolation 



Vacuum 

 Isolation 



The upper vessels in this figure are for dry air isolation, whereby the 

 deposition of moisture at the low temperature was prevented. In 

 each of these old forms it will be noted that a mass of phosphoric 

 anhydride placed in the lower portion is required to absorb traces 

 of water. The vacuum vessels described equally retard the loss as 

 well as the gain of heat (as shown in Fig. 3). 



such vessels are filled with liquid air and hot water respectively ; 

 scarcely any movement of the spot of light is seen when the silver side 

 is turned to the pile, but on rotating to the unsilvered side a strong 

 Vol. XXI. (No. 108) » 



