as was tliat of Jonker; perhaps very exact observations on colloïds, 

 the molecular weight of which is not too great, as for instance 

 tannin, may assist in clearing up this point. Sven Oden's^) solutions 

 of sulphur also, which melt sharply and reversiblj, seem to be a 

 favourable subject for the determination of the depression of the 

 freezing point, or, perhaps still better, of the osmotic pressure. 



If this idea is accepted, one must evidently reject Pi anck's opinion -) 

 that the alteration of the vapour pressure would afford a means ot 

 distinguishing between emulsion and real solution. Emulsions too 

 will show diminution of the vapour pressure, but in such a slight 

 degree, that it escapes observation. 



It is curious to note, that the workers in this field have made 

 their exj)eriments as if the colloid consisted of one phase, although 

 they were, of late at least, theoretically convinced, that it was composed 

 of two phases. A striking example is found in Jonkkr's second 

 paper'). This investigator takes a solution of tannin in water as 

 having two phases; when adding a definite amount of ether, he 

 observes a division into three liquid layers, the composition of which 

 is determined to 0,5 7o» 3,1 7o ^"^"d 44,3 "/„ tannin respectively. Now 

 he calls the system, at fixed pressure and temperature, an invariant 

 one, because it is composed of three components and three phases. 

 That is quite correct in my opinion; but, if one conceives tannin 

 in water two phases, why then does tannin in water with some 

 percentage of ether added suddenly become one phase ? ^^) 



Everyone who is acquainted with, for instance, Ostwald's Kolloïd- 

 chemie, will see, that my (Tonception is absolutely contrary to the current 

 views of the present time. I think this to be caused by the fact, that one 

 has gradually been led to confuse the notions "heterogeneous" and 

 "composed of several phases." Ostwald ^} for instance, says : colloi- 

 dal systems, especially colloïdal solutions, belong to the systems, 

 which are called in physical chemistry heterogeneous or plural phase 

 systems, and Fkeundlicii ") joins him by remarking, that it is appro- 

 priate to consider generally systems of two components to be two- 

 phase systems : real solutions, especially the dilute ones, form extreme 



1) Z. phys. Ghem. 80, 709. 



2) Thermodynamik, § 223, 3rd od., p. 205. 



3) Kolloïd-Zeitschr. 10, 126. 



"*) It will be evident, that I certainly think Jonker's determination of the critical 

 solution temperature of the two phases with a slight percentage of ether to be 

 conclusive. 



'') Grundriss der Kolloidchemie, 3rd ed., p. 23. 



*') Kapillarchemie, p. 308. 



