1084 
is not impossible. In the case of silica and alumina jellies, where 
the concentrated phase separates, an open structure is to be expected. 
Since the surface tension will probably be similar to that of water- 
glass — the gel is completely moistened by water —, the gel will 
not show von ScHRoEDER’s phenomenon. In fact, we did not find it 
(nor did vaN BEMMELEN), in apposition to Bancrort’s declaration, that 
gelatine and aluminium gel are theoretically equivalent. 
It is, therefore, possible to explain in this manner, why gelatine, 
swollei in water, loses water, when in a space saturated with vapour ; 
we should even be able to calculate the size of the drops by the difference 
of the vapour pressures of the gelatine swollen in vapour and in water. 
Von SCHROEDER has tried to measure this difference by allowing gelatine to 
swell in salt solutions and by determining the concentration of the solu- 
tion, in which the phenomenon no more appeared. He found this to be 
the case in a solution of sodium sulphate of a normality between 
10-5 and 10-°. This would give a difference in vapour pressure of 
+ 3.10 mm. of water, out of which the radius of the drops in the gel 
can be calculated to + 9 mm.'), evidently an impossible result. In 
fact, we have, in repeating voN SCHROEDER’s experiments, obtained 
different results: celloidin, swollen in a solution of 3°/, sublimate 
in absolute alcohol, does show the phenomenon. We intend to try 
to determine the difference of the vapour pressures by a direct 
method. If, on the other hand, we suppose the diameter of the drops 
in gelatine to be 5 wu’), we calculate, that the vapour pressures must 
differ + 100 mm. of water, which to us seems a rather high amount. 
There is, however, a serious objection to be raised against this 
explanation. The gel, swollen in liquid, loses water in the vapour; in 
consequence of which either cavities, filled with air and vapour, are 
formed, or the gel shrinks, according to its losing water. Silica jelly 
shows the first alternative, as is proved by its opaqueness, appearing 
at a certain point; gelatine, agar, celloidin and rubber, however, 
remain quite clear, but their volume is diminished. Now, tf there 
are no cavities, we do not see, why they should be formed anew, 
when the gel is replaced in the liquid. This objection, we think, 
entirely pulls down Bancrort’s theory. 
As to vON SCHROEDER’S remarks, we ape observe, that they do 
not give an explanation in the proper sense of the word. Von 
ScHROEDER Only wants to put an end to the controversy against the 
second law, by remarking, that the gel is taken from the liquid and 
2ad 
1) According to the formula: A p= = rp ee Chwolson, Lehrb. d. Phys. III, 
744), and assuming that the drops are ie 
*) 5 gp is the diameter of the capillary canals in silica jelly, as put by Zsigmondy. 
