( 964 ) 
In order to get a clear idea of the unulogy one should imagine a 
space containing water vapour in which are placed near each other 
a globular shaped imbibing substance (for instance a piece of sharply 
dried gelatin or gum arabic) and a drop of a liquid which is not 
readily volatile but easily mixes with water (for instance sulphuric 
acid or glycerin). Both now appear to be hygroscopic, both absorb 
water without loss of homogeneity; both ‘crease im size, because 
the volume of the mixture like that of the swollen substance is, 
approximately, additive and because the substance remains homo- 
geneous during the water absorption. By this dilation without loss 
of homogeneity ') the particles of the swelling body, like those of 
the sulphuric acid, or glycerin get further removed from each other: 
in both the disgregation, as ReINKE calls it, of these particles increases. 
If the two phenomena are Compare more closely, it appears in both 
cases that the water absorption is accompanied by a considerable 
evolution of heat and a decided contraction-of volume. There is only 
one point of difference between the two phenomena; the swelling 
body possesses the solid aggregation condition and retains the same 
during the absorption of the water whereas the miscible substance 
is liquid and remains liquid. 
This gulf is, however, more or less bridged over by what is 
observed in the substances with unlimited imbibition power. If, for 
instance, powdered gum arabic is allowed to take up moisture, il 
begins to cake when 30 "/, of water has been absorbed, with 40 °/, 
it forms a plastic mass, with 60°/, it is still solid but soft and 
when 110°/, has been absorbed a watery solution of gum arabic is 
obtained which becomes less viscous on further dilution. Ovoalbumin, 
peptone and dextrin behave in the same manner. Here we see how 
typical swelling substances gradually become aqueous mixtures, owing 
to water absorption. The two phenomena, therefore, not only resemble 
each other, but must be indeed closely related. Or perhaps even 
identical 7 
The older investigators have not dared to assent to the identity, 
1) One might perhaps object that the aqueous solution of gum arabic so formed 
is not a real but a colloidal solution. In the case of substances such as gum 
arabic, dextrin, and peptone, the difference between real and colloidal solution is 
but very slight. That this objection is not of great importance is shown by the 
fact that solutions of substances devoid of colloidal properties such as fructose 
(which has a low molecular weight and possesses normal values for the lowering 
of the freezing point and the elevation of the boiling point) are also gradually 
converted on drying (if crystallisation is prevented) into a solid substance having 
all the properties of a swelling substance. The sodium salt of glycerol-phosphorie 
acid behaves similarly. 
