THE COLLOIDAL STATE. 47 



over that rich in gelatine. It will be well to compare first 

 of all the laws governing this change in state, which is 

 so well characterized through the formation of two phases, 

 with the laws governing the solidification or gelation of 

 colloids, for which, as has already been discussed, a sep- 

 aration into two phases is also looked upon as a distin- 

 guishing characteristic. 



Investigations wKich have been carried on during 

 past years have, however, disclosed a whole series of 

 marked differences between these two processes, the 

 more important of which are now to be briefly touched 

 upon. 



The gelation velocity and the gelation- point of gelatine 

 are always more or less influenced through the addition 

 of crystalloids, which at times hasten, at other times inhibit 

 gelation, when compared with the gelation when pure water 

 only is used. This influence of the crystalloids is a pro- 

 gressive one and increases in proportion to the amount 

 added. 



The precipitation of gelatine is, on the other hand, 

 strictly connected with the addition of definite amounts 

 of the precipitating agent, amounts less than are sufficient 

 for actual precipitation being without effect. 



While all crystalloids modify the process of gelation, 

 even though they do this in different degrees and in 

 different directions, only certain crystalloids are precipi- 

 tatmg agents, while the others do not possess this power 

 even in the most concentrated solutions. Gelatine, for 

 example, is precipitated only through certain electrolytes, 

 non-ionized crystalloids being effective at no concentra- 

 tion. Non-conductors, such as urea and dextrose, can, 

 however, influence the process of gelation just as effectively 



