es 



cases, to be regarded as one-phase systems. This view, the conse- 

 quence of which would be, that an ordinary solution of salt would 

 consist of two phases, and that even one phase would be compo- 

 sed of separate molecules, is the fundamental difference between 

 OsTWALD and Freundlich on one side, and myself on the other. 

 As to this point I wish to refer to Bakhuis Roozeboom's clear repre- 

 sentation ^) of the fact, that the notion "homogeneous" is only a 

 relative one, and that, what is called by us a homogeneous system, 

 deserves this name only, because the molecules are so small and 

 our observations not delicate enough. When defining later the 

 "phase" ideal he speaks of homogeneous states (it is clear now, what 

 is meant by this), and further of internally uniform forms of appear- 

 ance of a substance, differing in state of aggregation, composition 

 or energy. Of course, one cannot speak of a state of aggregation, when 

 treating of molecules; further, the energy content of different mole- 

 cules will differ, so that one will have to consider each molecule as 

 a phase and there should be as many phases as molecules. Those, 

 who desire a more thermodynamical treatment of the idea phase, 

 will find it in van der Waals-Kohnstamm's text-book ^). When giving 

 a definition of phase, these authors claim that there must exist a rela- 

 tion between the different thermodynamical factors, potentials, pres- 

 sure and temperature. How can there be any question of that, so 

 long as we have not a complex, composed of numerous mole- 

 cules, whose number permits us to apply statistical methods ? To 

 carry the idea phase so far seems to me to be in complete contra- 

 diction to the notion itself, as we are used to apply it. An other 

 question is connected herewith. The defenders of the two-phase con- 

 ception add, that the systems are complicated by this fact, that the 

 surface of contact between the phases is very great, and that con- 

 sequently surface forces must play an important role. But this, too, 

 only holds good within certain limits; for, once more I put the 

 question, what, if one of the so-called phases is composed of sepa- 

 rate molecules — not an impossible state of affairs, when w^e think 

 of the size of albumen-molecules? Do the laws of surface action, 

 which are known to us, hold good in that case ? It requires no 

 argument to show that the special forces, which certainly come 

 into action in sharply curved surfaces, are always calculated and 

 measured in cases, in which we still have a great many molecules, 



1) Heterogene Gleichgewichte I, 9. 



') Vol II, p. ]1. Professor Kohnstamm was kind enough to direct my atten- 

 tion to the fact, that in the same book, vol. I, p. 123 the condition, that a phase 

 must consist of a great number of particles, is plainly stated. 



