Thin Fabric* and Films to Hydrogen and Helium. 211 



VI. Air Circuit. 



The air was let in through a T-tube A (see fig. 2), which 

 permitted the rate of flow to be varied by raising or lowering 

 the water level. With any given level the pressure was 

 adjusted so that the air always gently bubbled through the 

 base of the T-tube. In its course through the system the 

 air passed through a copper warming coil B and two tubes 

 filled with cotton wool moistened with glycerine so as to 

 eliminate all dust particles, as it was found that the intro- 

 duction of dust particles soon caused the soap films to rupture. 

 It was then bubbled through water and led through a gas- 

 meter which measured the rate of flow. From the gas-meter 

 the air, saturated with water vapour, was led through the 

 lower section of the film chamber, D ; sweeping out with it 



the hvdrooen gas which diffused through the film. From 



"... 

 there the air was dried in the phosphorus pentoxide tubes 



E and E', and tested by the katharometer K, finally bubbling 



out through the water in H at a pressure of about 1 cm. of 



water. 



VII. Gas Circuit. 



The gas circuit shown in fig. 2 was somewhat similar, 

 except that the gas was tested before entering the film 

 chamber by a purity meter P, of the katharometer type, 



Fig. 2. 



and then passed through the cotton wool tubes li and R', 

 bubbled through water in the bottle S, and thence to the 

 film chamber, and, finally, bubbled out through water in U, 

 at a pressure of about 1 cm. of water. The pressure of the 

 gas in the circuit was altered very slightly by adjusting the 

 tube (J, so that the film surface remained plane. The rate 

 of flow used was about 2 litres per hour. 



