380 



of 3 is then enveloped by (he liquid 2. If o\,3<^ó-j,3, ('Os a will be 

 negative, hence, a > 90° and the greater jjart of 3 is drawn into 

 the liquid 1. 



3. If now the phase 3 is suspended in the liquid 1 in the form 

 of a tine powder and this suspensio'n shaken with the liquid 2, three 

 things may occur. 



a. If <J2 3 > <5i,2 + ^51,3, 3 will be completely enveloped by 1 and 

 thus the suspension remains unchanged in 1. 



b. If ÖI 3 > ^1,2 + ^!,3, the stable condition will be such that 3 

 is completely enveloped by 2. The suspension will then disappear 

 from 2 and pass entirely into the liquid 2. 



c. If <J!,2 ^ ^2.3 + <^3,i. or none of the three contact surface 

 tensions greater than the sum of the other two, the powder is 

 deposited entirely on the surface of contact '). 



4. Let us now apply these considerations to colloidal solutions, 

 which according to modern views may be looked upon as transition 

 stages between suspensions, or emulsions, and true solutions. 



Let us first consider a suspensoid in which solid, floating particles 

 are supposed to be present. 



If these particles are fairly large and practically of uniform 

 dimension we may assume that tiie surface tension in regard to the 

 surrounding medium will be but Utile dependent on this dimension 

 and therefore, the same for all particles. The same three possibilities 

 which could be distinguished in the case of the coarse suspensions 

 will consequently apply here also. The colloidal substance remains 

 entirely in the first medium, passes entirely into the second or is 

 deposited quantitatively at the surface of contact, in the first case 

 the division coefficient = 0, in the second case it becomes go. 



If the size of the particles becomes smaller, the resultant of the 

 molecular attractions which appears as surface tension will be very 

 much dependent on the number of molecules which together form 

 the particle. Hence, the behaviour in regard to a second liquid phase 

 will become dependent on this size. For instance, it will then be 

 possible for particles below a certain size, to pass into the second 

 liquid, for particles of greater dimension to arrive at the contact 

 surface or to remain in the first liquid. According to the degree of 



1) histances of these different cases, a principle of separation for a mixture of 

 solid, insoluble substances which is based on the different behaviour in regard to 

 a liquidum couple, and the practical application thereof, are cited in a publication 

 in the Chemisch Weekblad. Vol 10, 700 (1913). Also compare J. B. Hofmann, 

 Zeitschr. f. physik. Chem. 83, 385 (1913). 



