﻿372 M. G. Quincke on the Capillary Phenomena 



markable, although smaller change of form of the air-bubble 

 took place. The thickness of the layer of liquid 3 is in the last 

 case less than 2/, or double the distance at which the molecular 

 forces of capillarity are still effective *. 



The change of form is, of course, more remarkable the more 

 a 2 and a=a 3 4-a 32 differ from one another — particularly striking 

 therefore with oil of turpentine and olive-oil. 



When flat drops of water or olive-oil are laid on a horizontal 

 glass plate sprinkled with lycopodium-powder, they have the 

 same form (inverted) as an air-bubble of equal volume in these 

 liquids, and a 2 could be determined from K— k in the same way 

 as for air-bubbles. The same holds good for large drops of 

 water which dew forms in the folds of certain leaves — cabbages 

 for instance. 



If on such flat drops of water a trace of olive-oil or oil of tur- 

 pentine, or on a flat drop of olive-oil a trace of oil of turpentine 

 is placed, then the drop immediately becomes flatter and broader ; 

 hence a change of form occurs as in air-bubbles. 



Owing to the difficulty of obtaining flat drops of water and 

 oil of large diameter on glass plates, I have abstained from ma- 

 king measurements of these changes in form. 



13. If on the surface of flat drops of a liquid 1 in air a small 

 quantity of a liquid 3 be placed, which spreads itself out on this 

 surface, then in the equations (pa) to (14a) of § 11 we may sup- 

 pose 



<r 2 = 0, a 32 =a 3 . 



On flat drops of mercury in air small drops of water, olive-oil, 

 and oil of turpentine were placed. As soon as these spread out 

 on the surface of the mercury, the drops are seen to become 

 flatter and broader. 



In the following Table a few observations are collected : — 



* I will take this opportunity of remarking that I committed an over- 

 sight in a communication on the magnitude oH{Gdtt, Nachr. 1869, p. 217, 

 Pogg. Ann. vol. cxxxvii. p. 403, 1869), when I said that, according to 

 the views of Plateau, a thin film of a liquid could not exist when its thick- 

 ness became -<2l. The experiments which I cited (Plateau, "Rech. Exp. 

 &c. 5 e ser.," Mem. de Brux. vol. xxxiii. p. 44, 1861) appeared to me to justify 

 this assumption ; whilst Plateau only supposes the capillary pressure of a 

 curved film of the liquid of the thickness D dependent on the same when 

 D < 21: compare Plateau, " Rech. Exp. 2 e ser.," Mem. de Brux. vol. xvi. p. 

 35 (1847). 



