116 PROTOPLASM 



the liquid imbibed need not always be water, the term should be 

 more general. He therefore proposed lyophobic and lyophilic 

 (Gr. lyos, solution). These names are now the most generally 

 used. Numerous other names have been suggested. They 

 indicate the many ways in which the two groups can be 

 distinguished. 



Lyophobic colloids Lyophilic colloids 



Hydrophobic colloids Hydrophilic colloids 



Anhydrophilous colloids Hydrophilous colloids 



Irreversible colloids Reversible colloids 



Typical or genuine colloids Baser colloids 



Unstable colloids Stable colloids 



Electrosensitive (electrocratic) colloids Electroresistant colloids 



Suspension colloids Emulsion colloids 



Suspensoids Emulsoids 



Nongelatinizing type Gelatinizing type 



Colloidal suspensions Colloidal solutions 



The colloidal systems (lyophobes) referred to in the foregoing 

 left-hand column are of three major kinds — solid, liquid and 

 gaseous suspensions (metal sols, emulsions, and foams). Sub- 

 groups under the lyophilic systems include the turgescent and the 

 nonturgescent gels, that is to say, gels which swell and those which 

 do not. Gelatin is a turgescent or swelling gel, while silica gel 

 is nonturgescent. The former is elastic, while the latter is (rela- 

 tively) inelastic. They differ also in that the nonturgescent type 

 becomes porous on drying, while the turgescent type does not. 

 In view of the fact that the swelling or turgescent gels (gelatin) 

 are elastic and nonporous, while the nonswelling or nonturgescent 

 ones (silica) are nonelastic and porous, it does not matter which 

 property we use upon which to classify them, for it is the same 

 in the end, and our choice really rests on that property in which 

 we are primarily interested. 



Any classification of colloids built on physical properties is, 

 in the present state of our knowledge, certain to be an artificial 

 one. The lyophobes (suspensions of metals or oils) present, in 

 the main, a natural group. The lyophiles, on the other hand, 

 are an unnatural and heterogeneous collection, natural subgroups 

 among them being the soaps, the carbohydrates (agar, dextrin, 

 cellulose), and the proteins. Zsigmondy evolved a classification 

 based on chemical rather than physical properties. While 



