276 Prof. McLennan and Mr. Shaver on P ermeahllity of 



allowed to fall on the film at short intervals (say, every two 

 or three minutes), the flow being regulated by a clamp on 

 the rubber tubing. The excess solution drained off the edges 



Fig. 1. 



*M 



KSSSS'sXSSSSSSSSSSSSSSSSSSSSSSSSSSS^ 



of the film into the lower section of the chamber. In this 

 way the film was kept at a practically constant maximum 

 thickness and the variations in diffusion due to changes in 

 the film were eliminated as far as possible. 



