381 



dispersion, colloidal solutions of a same snbstance will behave in a 

 different manner. 



If finally the colloidal particles exist of a few molecnles only the 

 idea of snrface and surface tension loses its sio-nificance. The solution 

 is then an ordinary molecular one and the dissolved substance will 

 distribute itself over both liquids according to the "dividing rule". 

 Other factors than surface tension, tlien dominate the distribution 

 over the two phases. 



5. Some complications may still occur owing to the fact that the 

 particles deposited at the surface of contact do not keep apart but 

 unite to larger coagulums. This may happen very readil}^ with very 

 instable solutions. 



In the case of emulsoids or solutions in which floating droplels 

 of liquid must be assumed, these, if deposited at the contact surface 

 may unite to form a separate liquid layer when öj^o <C ^2,3 + «>3,i- 

 If however the separation has taken place at the contact surface, 

 because none of the three surface tensions w^as greater than the sum 

 of the other two, the expansion of liquid 3 between 1 and 2 

 becomes impossible and the isolated droplets of 3 will unite with 

 greater difficulty. 



6. In order to prove these considerations experimentally, I have 

 investigated the behaviour of a few different colloidal solutions 

 towards a second liquid. A few provisional results are communicated 

 here. 



In the first place, colloidal gold. 



A red gold solution was obtained by passing CO into a dilute 

 solution of AuCls. If into this solution was dropped cautiously 

 i^obutylalcohol or an aqueous solution of the same, the colloidal 

 solution remained unchanged. Not a trace of coagulation which 

 would show itself by a change of colour to bluish-violet \Ya,s obser- 

 ved. Hence in homogeneous solution /^-fbutylalcohol has no influence 

 on the stability of the colloidal gold solution. 



As soon, however, as the limit of solubility of the isobutylalcohol 

 had been exceeded and this begun to form a separate layer, the 

 gold, on shaking, gradually disappeared from the water and collected 

 at the surface of contact. This then assumes a splendid colour, 

 blue in transmitted, and a golden lustre in incident light ^). 



1) As the alcohol layer does not moisten the glass owing to a thin layer of 

 water collecting between the alcohol and the glass, the whole of the alcohol 

 phase (upper layer; is surrounded at the nether side and the glass walls by a 

 water-alcohol demarcation in which the gold is distributed very homogeneously. 

 At first we thus gel the impression that the alcoholphase itself was coloured, ff, 



