Mr. T. Graham on Liquid Diffusion applied to. Analysis. 379, 



seen in colloids. In the properties 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 (regulation of Faraday) of 

 masses of melting ice, when placed in contact, has much of a 

 colloid character. A colloidal view of the plasticity of ice demon- 

 strated 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 Funke, a soft 

 and gelatinous albuminoid body is seen to assume a crystalline 

 contour. Can any facts more strikingly illustrate the maxim 

 that in nature there are no abrupt transitions, and that distinc- 

 tions of class are never absolute ? 



8. Osmose. 



Little has been said in the present paper respecting osmose, 

 a subject closely connected with colloidal septa. It now appears 

 to me that the water-movement in osmose is an affair of hydra- 

 tion and of dehydration in the substance of the membrane or 

 other colloid septum, and that the diffusion of the saline solu- 

 tion placed within the osmometer has little or nothing to do 

 with the osmotic result otherwise 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 diffu- 

 sion 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 move- 

 ment is possible. 



The degree of hydration of any gelatinous body is much affected 

 by the liquid medium in which it is placed. This is very obvious 

 in fibrine and animal membrane. Placed in pure water, such 

 colloids are 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 



