188 
melting ice the temperature of B could be held at 0° throughout the neces- 
sary time interval. For the series II, a trough of special design to contain 
liquid air was used. This was made of three layers of thin sheet tin, with 
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' 
' 
; 
a U shaped cross section, nested together with thick layers of felt be- 
tween. This is shown in the lower part of Fig. 1. 
A small quantity of anhydrous quartz powder was placed in the tubes 
A and B, and uniformly distributed in a thin line along the bottom of the 
tubes by rocking the frame about O, and gently tapping the tubes with a 
