224 
jME. t. geaham on liquid dipfusion applied to analysis. 
saline matter of the membrane through its whole thickness. The advantage which 
colloidal solutions have in inducing osmose, appears to depend in part upon the low 
ditfusibility of such solutions, and their want of power to penetrate the colloidal septum. 
The substances fibrin, albumen, and animal membrane swell greatly when immersed 
in water containing minute proportions of acid or of alkali, as is well known. On the 
other hand, when the proportion of acid or alkali is carried beyond a point peculiar to 
each substance, contraction of the colloid takes place. Such colloids as have been named 
acquire the power of combining with an increased proportion of water, and of forming 
superior gelatinous hydrates, in consequence of contact with dilute acid and alkaline 
reagents. Even parchment-paper is more elongated in an alkaline solution than in pure 
water. When so hydrated and dilated, the colloids present an extreme osmotic sensi- 
bility. Used as septa, they appear to assume or resign their water of gelatination under 
influences apparently the most feeble. It is not attempted to explain this varying 
hydration of colloids with the osmotic effects thence arising. Such phenomena belong 
to colloidal chemistry, where the prevailing changes in composition appear to be of the 
kind A'aguely described as catalytic. To the future investigation of catalytic affinity, 
therefore, must we look for the further elucidation of osmose. 
