on Mixtures of Alcohol and Water. 3 



was generally due to a fault within the cell-wall, but not 

 always ; sometimes the leak was through the glass at the 

 joint being strained or through the joint itself. 



The cells were very hard and close-grained, having walls 

 between *4 cm. and *5 cm. thick. Their internal length was 

 about 6*5 cm., and their internal diameter 1*6 cm. A few 

 cells of more porous clay and slightly thinner walls, kindly 

 given by Mr. Whetham, were also used and proved very 

 serviceable. 



The cell was prepared by washing in dilute alkali and then 

 in dilute hydrochloric acid. It was then washed and boiled 

 in several changes of distilled water and allowed to become 

 nearly dry. Close-fitting glass tubing was ground into the 

 end of the cell by means of wet emery-powder, and was fixed 

 by litharge and glycerine cement. This hardens to a mass 

 apparently unaffected by alcohol. This cement is rather 

 porous, and any flaw in it may make it impossible to obtain a 

 sound membrane. There is always the same risk of failure 

 du3 to want of uniformity in the cells themselves. The joint 

 obtained by using sealing-wax is more suitable for formation 

 of the membrane, but had to be abandoned on account of the 

 ease with which it is attacked by alcohol. Of the cells 

 with sealing-wax joints a much larger percentage proved 

 sound. 



The air in the pores of the cell was driven out by means of 

 electric osmose and afterwards by placing under the water- 

 pump and drawing freshly boiled distilled water, still slightly 

 warm, through the cell-walls. Its own volume of water was 

 drawn through several times. In the case of the more porous 

 cells, drawing water through in this way seemed sufficient. 

 The cell was then placed in copper-sulphate solution and was 

 filled with potassium ferrocyanide solution. With the harder 

 cells, ten to fourteen days in these solutions seemed necessary 

 for the formation of a useful membrane. The cell was then 

 fitted with a gauge and tested by a sugar solution of known 

 strength. 



In the gauge attachments there were two T-pieces arranged 

 in H form. Below one vertical portion was the cell ; below 

 the other the gauge was fixed. In this way the cell and 

 gauge could readily be washed out without detaching the 

 gauge. The opening immediately above the cell was closed 

 by thick-walled rubber tubing wired over a flange on the 

 glass, and a screw-clip. The opening above the gauge was 

 closed by fusing the drawn-out glass. The rubber tubing 

 made it possible to add pressure by means of a pump, and to 



B 2 



