﻿468 M. G. Quincke on the Capillary Phenomena 



great number of other experiments on outspreading have been 

 made. 



The appearance which the spreading usually presents is that 

 particles of dust on the free surface of liquid 1 are repelled by 

 it, or that liquid 2, spread out to a thin layer, shows Newton's 

 coloured rings. By means of the foreign substances sticking 

 to the particles of dust, however, the surface of the liquid is 

 easily rendered impure ; and optical methods are insufficient, as 

 soon as the superposed layer of liquid becomes too thin, or the 

 two liquids have nearly the same refractive indices. 



As the substances brought into contact with one another, either 

 through reciprocal solution or chemical influence, change their 

 capillary constant, or even form entirely new chemical combina- 

 tions, in which the atmospheric air and the moisture con- 

 tained in it must be particularly considered, so in many cases a 

 result can be observed to which the laws given in § 2 appear 

 to be in contradiction. On a proper criticism of the methods 

 used by different observers and the facts discovered by these 

 methods, they will all be found in agreement with the theory. 



A great portion of the experiments on spreading known to me 

 can be estimated by the numerical data of Table X. § 10. The 

 magnitude of the unknown capillary constants of the common 

 surface of two liquids can in many cases be approximately esti- 

 mated, if it be remembered that generally a 12 is less the more 

 liquid 1 is dissolved by liquid 2, or conversely. 



For easy comparison of the theory with the results obtained 

 by other observers, I give the capillary constant u at the mean 

 temperature for a few liquids. 



a. 



Observer. 



milligrms. 





Ether 1-815 



Aqueous alcohol . . 2*589 



Wilhelmy* 

 Bedef 



(spec. grav. - 842) 

 Soap -water (^ soap) 3*22 

 Glycerine . . . . 5-143 



Plateau J 

 Wilhelmy§ 



The series standing under the names of the respective obser- 

 vers are so arranged that the lower liquid always spreads out on 

 the upper. 



* Pogg. Ann. vol. cxxi. p. 52 (1864). 



t Mem. Cour. Sav. Etr. Brux. vol. xxx. p. 160 (1860). 



X Recherches &c. 8 e ser. Mem. Acad. Brux. vol. xxxvii. p. 91 (1868). 



§ Pogg. Ann. vol. cxxii. p. 13 (1864). 



