]ME. T. GEAHAM ON LIQUID DIFFUSION APPLIED TO ANALYSIS. 
223 
softness of pitch, has the elasticity and tendency to rend seen in colloids. In the pro- 
perties last mentioned, ice presents a distant analogy to gum incompletely dried, to 
glue, or any other firm jelly. Ice further appears to be of the class of adhesive colloids. 
The redintegration (regelation of Faeaday) of masses of melting ice, when placed in 
contact, has much of a colloid character. A colloidal view of the plasticity of ice 
demonstrated in the glacier movement will readily develope itself. 
A similar extreme departure from its normal condition appears to be presented by a 
colloid holding so high a place in its class as albumen. In the so-called blood-crystals 
of Fuxke, a soft and gelatinous albuminoid body is seen to assume a crystalline contour. 
Gan any facts more strikingly illustrate the maxim that in nature there are no abrupt 
transitions, and that distinctions of class are never absolute 1 
8. Osmose. 
Little has been said in the present paper respecting osmose, a subject closely con- 
nected with colloidal septa. It now appears to me that the water movement in osmose 
is an affair of hydration and of dehydration in the substance of the membrane or other 
coUoid septum, and that the difiusion of the saline solution placed within the osmometer 
has httle or nothing to do uith the osmotic result, otherudse than as it affects the state 
of hydration of the septum. 
Osmose is generally considerable, through membranous and other highly hydrated 
septa, with the solution of any colloid (gum, for instance) contained in the osmometer. 
Yet the diffusion outwards of the colloid is always minute, and may sometimes amount 
to nothing. Indeed, an insoluble colloid, such as gum-tragacanth, placed in powder 
within the osmometer, was found to indicate the rapid entrance of water to convert the 
gum into a bulky gelatinous hydrate. Here no outward or double movement is possible. 
The degree of liydration of any gelatinous body is much affected by the liquid medium 
in which it is placed. This is very obnous in fibrin and animal membrane. Placed in 
pure water, such colloids aro hydrated to a higher degree than they are in neutral 
saline solutions. Hence the equilibrium of hydration is different on the two sides of the 
membrane of an osmometer. The outer surface of the membrane being in contact with 
pure water tends to hydrate itself in a higher degree than the inner surface does, the 
latter surface being supposed to be in contact with a saline solution. When the full 
hydration of the outer surface extends through the thickness of the membrane and 
reaches the inner surface, it there receives a check. The degree of hydration is lowered, 
and water must be given up by the inner layer of the membrane, and it forms the 
osmose. The contact of the saline fiuid is thus attended by a continuous catalysis of the 
gelatinous hydrate, by which it is resolved into a lower gelatinous hydrate and free 
water. The inner surface of the membrane of the osmometer contracts by contact with 
the saline solution, while the outer surface dilates by contact with pure water. Far 
from promoting this separation of water, the diffusion of the salt throughout the sub- 
stance of the membrane appears to impede osmose, by equalizing the condition as to 
