200 ANNUAL OF SCIENTIFIC DISCOVERY. 



action ; the action will be equal on both sides, and although probably 

 attended with movements of the fluids, yet nothing will be indicated, 

 as the movements, being equal, and in opposite directions, will neu- 

 tralize each other. 3. That difference of composition in the two 

 fluids is necessary in order that there may be inequality of action on 

 the two sides of the membrane. 4. That no substance appears to be 

 permanently deposited in the membrane during osmosis. 5. That 

 the action upon the membrane is of a solvent nature. 6. That prob- 

 ably the chemical actions on the two sides of the membranes do not 

 depend upon inequality, simply of one kind of action, but upon a 

 difference of chemical actions going on on the two sides of the mem- 

 brane. 



In these observations, and in the various experiments which he in- 

 stituted, Professor Graham, to a certain extent, traced osmosis to the 

 effects of changes occurring in the intervening septum ; and although 

 in 1854 he did not give that defined view of the cause of osmosis 

 which he has since supplied, he removed many preceding errors, and 

 laid the basis for a more comprehensive understanding of the whole 

 subject. 



In his latest paper, published during the past year (1861) in the 

 Proceedings of the Royal Society, and entitled "Liquid Diffusion 

 applied to Analysis," he has led us to a new view of the osmotic pro- 

 cess, and, without impairing the facts previously observed, has given 

 to them a reading which is at once simple and practical. Still set- 

 ting aside the idea of capillarity as the cause of the phenomena ob- 

 served, still setting aside the idea of a difference of specific gravity 

 in two fluids as the cause of the phenomena observed, he has indi- 

 cated that the phenomena are traceable to an influence exerted on 

 the various substances in water by the membrane interposing, and 

 has accounted for separations, and proposed analytical results, all 

 most singular in character and striking in simplicity. 



If Professor Graham be now correct, all chemical substances are 

 divisible into two great families in respect to their diffusive qualities. 



The first, or diffusive class of substances, are marked by their ten- 

 dency to crystallize either alone or in combination with water. 

 When in a state of solution they are held by the solvent with a cer- 

 tain force, so as to affect the volatility of water by their presence. 

 The solution is generally free from viscosity, and is always rapid. 

 Their reactions are energetic and quickly effected. To this class he 

 gives the name of Crystalloids. 



The other class of substances of less diffusibility appear to be typi- 

 fied by animal gelatine. They have little if any tendency to crystal- 

 lize, and they affect a vitreous structure. To this class he gives the 

 name of Colloids. 



The distinctions between the crystalloids and the colloids, as chem- 

 ical substances, are further defined by Professor Graham in the fol- 

 lowing descriptions : The planes of the crystal, with its hardness 

 and brittleness, are replaced in the colloid by rounded outlines, with 

 more or less softness and toughness of texture. Water of crystalliz- 

 ation is represented by water of gelatination. Colloids are held in 

 solution by a feeble power, and have little effect on the volatility of 

 the solvent. They are also precipitated from their solution by the 



