188 



melting ice the temperature of B conlcl be lield at 0° tliroughout 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, witli 



Fig. 1. 



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 E, 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 



