Memoir of Thomas Graham. 121 



made by previous experimenters, showed that this whole chtss 

 of phenomena are essentially similar, and called this manifesta- 

 tion of power simply "osmose." 



While studying osmotic action, Graham was led to one of Ins 

 most important generalizations,— the recognition of the crystal- 

 line and amorphous states as fundamental distinctions in chem- 

 istry. Bodies in the first state he calls crystalloids: those in 

 the last state, colloids (resembling glue). That there is a dif- 

 ference in structure between crystalloids, like sugar or telds].ar. 

 and colloids, like barley candy or glass, has of coiirse always 

 been evident to the most superticial observer : but Graham was 

 the first to recognize in these external ditferences two funda- 

 mentally distinct conditions of matter not peculiar to certain 

 substances, but underlying all chemical ditferences, and ajipcar- 

 ing to a greater or less degree in every substance. He showed 

 that the power of diffusion through liquids depends very much 

 on these fundamental differences of condition,— sugar, one of 

 the least diffusible of the crystalloids, diffusing fourteen times 

 more rapidly than caromel, the corrcsjionding colloid He also 

 showed that, in accordance with the general chemical rule, while 

 colloids readily combine with crystalloids, bodies lu the same 

 condition manifest little or no tendency to chemical union. 

 Hence in osmose, where the membranes employed are invariably 

 colloidal, the osmotic action is confined almost entirely to crys- 

 talloids, since they alone are capable of entering into that com- 

 bination with the material of the septum on which the whole 

 action depends. r i ^ 



On the above principles Graham based a simple method ot 

 separating crystalloids fi-om colloids, which he called "dialvsis/ 

 and which was a most valuable addition to the means of chem- 

 ical analysis. A shallow tray, prepared by stretching parchment 

 paper (an insoluble colloid) ovei " ^ - i- - -- * -- 



apparatus required. The solu 

 into this tray, which is then floated on pure water, whose volume 

 should be eight or ten times greater than that of the solution. 

 Under these conditions the crystalloids will diffuse through the 

 porous septum into the water, leaving the colloids on the tray, 

 and in the course of a few days a more or less complete sejiara- 

 tion of the two classes of bodies will have taken place. In this 

 way arsenious acid and similar crystalloids may be s^eparated 

 from the colloidal materials with which, in the case of poison- 

 ing, they are usually found mixed in the animal juices or 

 tissues. " .,.11 



, ^„,_ practical applications, the method 



the hands of Graham yielded the most startling 

 8," developing an almost entirely new class of bodies as the 

 (lal forms of our most familiar substances, and justifying 



