1082 / 
that the difference, which Foorr speaks of (7 m.G.), is out of pro- 
portion to the differences, found by us (a hundred and more m.G.). 
We now wish to proceed to consider the given explanations. 
In doing this the first question that suggests itself is, whether the 
examined substances are composed of one or of two phases. Since 
van BEMMELEN and Harpy’s investigations it is pretty generally 
assumed, that gels are systems of two phases. As to bodies like 
silica, we do not oppose this statement; but for gelatine, celloidin 
and rubber, it does not seem to be at all certain. Let us examine 
the grounds, on which it is based : 
1. the well-known “Umschlagpunkt” and the behaviour of silica 
jellies (VAN BEMMELEN); agar, gelatine, cellofdin, and rubber do not 
show a sim:lar behaviour. 
2. the pressing experiments; these do not prove anything. In 
the same way, one can expel the water from a salt solution, by 
exposing it to a pressure that exceeds the osmotic one, in a pot 
with semipermeable walls. Under these circumstances some water is 
pressed out; but nobody will maintain this solution to be a system 
of two phases. In the case of agar the canvas, between which the 
agar is pressed, acts as a semipermeable membrane. 
3. the analogy to mixtures of water, alcohol and gelatine, in 
which Harpy *) succeeded in observing the separation of small drops. 
Leaving the question, whether the drops appear just at the point of 
solidification, out of discussion, we are not allowed to apply results, 
obtained in a ternary system, to a binary one’). 
+. the behaviour of gelatine and agar, which are soluble in water, 
when liquid, but insoluble, when solidified, whilst the solution generally 
solidifies as a whole. If one takes the hysteresis into account it does 
not seem impossible to explain this behaviour also in a system of 
only one phase. 
5. the structures found by Bürscuur. These however do not seem 
to be of much value, since they are on the limit of the power of the 
microscope and since they have to be called into existence by all 
sorts of artificial means. Moreover Zsicmonpy and BACHMANN®) have 
lately shown, by using the ultramicroscope, that both silica gel and 
gelatine are built up of much finer elements. It is doubtful though, 
if in this case we can speak of “phases”. We too think it very 
likely, that molecular aggregates are formed in solutions of gelatine; 
but these are also to be observed (by means of the ultramicroscope) 
1) Z. phys. Chem. 33, 326. 
2) BACHMANN, Z. Anorg. Chem. 78, 125 expresses the same opinion. 
3) Z. anorg. Chem. 71, 356; 73, 125. 
