61 



solutions. From the formula F=n-\-3 — r it would indeed follow, 

 that the freezing; point depends on the concentration, whereas 

 F =^ n -\- 2 — r would lead to the conclusion, that the freezing 

 point does not varj with the concentration, which is in agreement 

 with the observations. 



It seems to me that new light is thrown upon these questions, if 

 we take a view, which was brought forward, a few years ago, by 

 Einstein and Perrin. Our starting-point then will be Einstein's 

 declaration "') that the only ditFerence between a dissolved molecule 

 and a suspended body lies in their size, and that one cannot see, 

 why a number of suspended bodies should not exert an osmotic 

 pressure just as well as a number of dissolved molecules. It will 

 be superfluous to point out, how rich in results this conception has 

 become in Perrin's hands. I only wish to mention that Perrin ^), 

 with the help of considerations on (hat very osmotic pressure, 

 deduced a formula for the distribution of a suspension under the 

 influence of gravity, ^vhich was fully confirmed b}^ the experiments. 

 Should objections be raised against his reasoning, Lorentz') has 

 shown, that the formula can be obtained with perfect strictness. 

 Moreover we find it developed by van der Waals — Kohnstamm^) 

 in a third way; in fact these authors apply to Perrin's suspensions 

 a formula, deduced rigorously for ordinary diluted solutions, only 

 making those alterations that are necessary aud permissible because 

 of the enormous molecular weight of one of tiie components. It is 

 quite evident from all this, tliat suspended granules may reallj^ be 

 treated as enormous molecules. 



Now it is onl}^ a short step to the conception, which I propose, 

 namely, that a colloidal substance must be considered one phase, as 

 well as a solution of sugar in water is one phase. Let us confine 

 ourselves for the present to the sols, cases, that are usually treated 

 as suspensions or emulsions. For these the given conception leads 

 to the conclusion, that they really exhibit a diminution of the vapour 

 pressure, that, therefore, the freezing point changes with the con- 

 centration, but at the same time it shows this dapression to be 

 exceedingly small, because the molecular weight or the quantity, 

 which we may in this case regard as such, the weight of the 

 particles floating in the liquid — is so considerable. The proposed 

 assumption is therefore in agreement with the experimental results, 



1) Ann. d. Phys. [4] 17, 549. 



2) Ann. d. Ghim. et de Phys. 8e Sér. T. 18. 



3) Ghem. Weekbl. 7, 827. 



*) Lehrb. der Thermodyn. 11, p. 567. 



