THE COLLOIDAL STATE. 53 



as soon as the colloid solidifies, can be readily shown to 

 be untrue through the production of precipitates in clear, 

 solidified gelatine. For, since the precipitation limits of 

 many electrolytes, such as the sulphates, citrates, and 

 tartrates of the alkali metals, are dependent upon tem- 

 perature in such a way that they are lowered with a de- 

 crease in the temperature, it is an easy matter to prepare 

 salt-gelatines in which heavy precipitates do not appear 

 until the solidification temperature has been long passed 

 in other words, in the clear and solid gelatine. Such 

 coagulations are subject to the well-defined effects of 

 coagulation "germs" in the same way as those which 

 occur in a fluid medium. The beautiful figures which 

 LIESEGANG has been able to produce in colloids with 

 the aid of precipitates all rest, in the main, upon the 

 ''germ" action of previously produced coagulations. In 

 such processes is also found an unforced explanation of 

 the phenomenon, used by BUTSCHLI as an argument in 

 favor of the existence of a primary honeycomb structure, 

 that delicate granules when suspended in gelatine are 

 always found in the nodal points and walls of the frame- 

 work. The reason for this is that these foreign bodies 

 all act as coagulation germs. For the same reason, the 

 chambers of the honeycomb structure arrange themselves 

 in rows which correspond with the lines produced on 

 the slide in polishing it. And just as little will we be able 

 to consider it proof of a preformed foam structure that 

 the coagulations which take place in colloids mirror all 

 the stresses that appear in it, due in part to shrinkage 

 while drying, in part to the contraction of cooling air 

 bubbles. 

 As further support for belief in a preformed structure, 



