340 



Dr. G. Bakker on the 



consist of different parts. For a first set of films he has founo\ 

 according to the experiments of Remold and Rlicker, a 

 thickness between 40 and 12 fifi. If the atmosphere of 

 the space wherein the liquid films were formed was not 

 saturated, he obtained a film of about 6 jx^i. 



In a second investigation * Johonnott has continued his 

 research by the aid of a Michelson's interferometer. In 

 order to obtain a thickness which could be measured with 

 sufficient exactness, he produced, in a long box of brass, 

 221 films of soap-water parallel behind each other. The 

 relation between the temperature and the average thickness 

 of the films may be represented by fig. 3. 



Jlxis of fiempe7-vLtu.rc 



26 



By careful examination with the microscope, Johonnott 

 could often distinguish in the black spots five parts of differ- 

 ent thickness. The minimum value of the thickness of the 

 films was circa 6 //,//,. Although the vapour in the bow of 

 Johonnott toas mixed with air, I believe that ive may thus 

 safely adopt also in the ease wherein the films are only in con- 

 tact with saturated vapour, 6 y^i as the order of magnitude of 

 the minimum thickness of the plane capillary layer. Now I 

 have demonstrated above that the two capillary layers which 

 limit a liquid film cannot touch one another, and that the 

 thickness of the plane capillary layer is circa the third part 

 of the minimum value of a liquid film. "We find thus for the 

 thickness of the plane capillary layer circa 2 jxfi. The fact 

 that the two capillary layers which limit a liquid film cannot 

 touch one another, and that therefore each liquid film 

 must consist of a layer of liquid limited by two complete 



L. c. xi. (1906) pp. 746-753. 



