>;04 Professor Sir James Dewar [June 21, 



Kate of Extension of Black across Films of Soap 

 Solution. 



E.rhausted Vessels. 



Film 3 cm. diameter, in vertical plane. mm per minute. 



On glass neck 0-20 to O-Qo 



On wire ring 0-33 to 0-16 



On glass frame, 6 cm. x 1 cm. 



Long side vertical 4'0 to 0*4 



Short side vertical 0-2 to 0-01& 



Film 3 cm. diameter, in horizontal plane ... 0-09 



Unexhausted Vessels. 

 Films in vertical plane, across glass bottle. 



19 cm. diameter 0-24 to 0-16 



3 „ „ 0-06 to 0-02 



Film in horizontal plane, across glass bottle. 



3 cm. diameter 0-12 to 0-1& 



Alteratioyi of Inclination of Plane of Film. 



Film on rectangular frame in exhausted vessel. 



Inclined 10- to horizontal ... 0*04 to Q- 01 after 7 hours. 

 „ 20° .„ ... 0-15 



40° „ ... 0-305 



In an horizontal film the black circle increased in diameter from 

 <S to 32 mm. in about 4 hours, the actual rate being 0*11 mm. per 

 minute. It follows that the gravitational effect is considerable. 



A 3 cm. film of 2 per cent potass oleate in 50 per cent glycerin,, 

 after being freshly thrown, gave a rate of • 05 mm. in a vertical 

 plane. After the same film had become completely black and 

 drained, it was re-thickened from the remaining Gibb ring by 

 rotation. The rate then measured was 0*2 mm. through the upper 

 third, 0*5 mm. in the equatorial j^art, and 0"3 in the lower one-third. 

 This was again repeated, when the corresponding figures were 1 • 6, 

 5'0 and 1-6. It would thus appear that when the Gibb ring i& 

 forcibly deprived of liquid it exerts a very powerful attraction to any 

 liquid in the neighbouring film, quickly draining it to the black 

 condition when the neighbouring surfaces are well drained. 



Generally speaking, solutions of potassium soaps thin rather more 

 slowly than sodium soaps of the same composition, and both are much 

 slower than comparable concentrations of ammonium soaps. These 

 last are very sensitive to small variations of ammonia from neutrahty. 

 becoming slow when the ammonia is in defect, and vice versa. As 

 regards the percentage of glycerin, as would be expected, increasing 

 concentration reduces the mobihty and rate of development of the 

 l»lack, whicli rate, however, is then more sensitive to changes of 

 temperature than ai'e those solutions having less glycerin. A plane 

 vertical circular film II) cm. diameter, containing 5 to 10 per cent 

 excess of ammonia over neutral oleate in 50 per cent glycerin, gave 



