518 Dr. Parks on the Thickness of the Liquid Film 



In the first experiment some cotton silicate, similar to that 

 used in the author's previous investigation *, was packed 

 tightly into a test-tube and the mouth of the tube was drawn 

 out to a line neck, but not sealed. 



The weight of the silicate was 3'37 grammes, the average 

 diameter of the cylindrical filaments was "00175 cm., the 

 sp. gr. was 2*7, and the estimated area of surface was 

 847 sq. cm. per gm. 



Hence the superficial area of the silicate was 3*37 x 847 — 

 2854 sq. cm., and allowing for the area of surface of the test- 

 tube, the whole area of glass surface amounted to about 

 2900 sq. cm. 



The tube was placed in an open beaker, and this was 

 covered with a large inverted beaker standing over some 

 water in a shallow tray and kept in a closed glass cupboard 

 at nearly constant temperature. 



The vapour which filled the chamber slowly diffused into 

 the test-tube through the narrow aperture, and became 

 condensed on the surface of the glass. The experiment 

 continued for 16 days, the tube being weighed at intervals. 

 The outside of the tube was wiped with a clean cloth before 

 each weighing, so that the observed increase of weight was 

 entirely due to condensation by surface-action. The tem- 

 perature never varied much from 15° C. The following table 

 shows the results of the various weighings and the estimated 

 thickness of the film of moisture. The initial weight of the 

 tube and silicate when dry was 9*3402 grammes. 



rrv Weight of tube Increase of 



and silicate. Weight. 



Estimated 

 thickness of 

 film (cm.). 



12 hours 9-3602 '0200 6-9xH)j! 



1 day 9-3644 '0242 8-3x10 ° 



2 days 93672 -0270 9-3x10° 



4 „ 9-3710 



10 „ 9-3774 



15 „ 9-3790 



16 „ 9-3790 



•0308 10-6x10 



•0372 12-8x10" 



•0388 13-4x10' 



•0388 13-4x10" 



In another experiment the silicate was placed loosely in 

 the tube and the mouth of the tube was allowed to remain at 

 its ordinary width, about 1*5 cm. The experiment was made 

 much more quickly than the first one, but the final result 

 was the same, 



* Phil. Mag. [6] iv. p. 246 (1902). 



