ALUMINIUM HYDROXIDE BY ELECTROLYTES. 19 



the purpose of comparison of various electrolytes amoug them- 

 selves, it will be more convenient to chose certain characteristic 

 points on the curves, than to employ the curves themselves ; 

 and the distinct points which are particularly well fitted for the 

 purpose seem to be those above mentioned, viz. : the concentra- 

 tion of the incipient coagulation, and the lowest concentration 

 at which complete coagulation takes place. 



The smallest concentration of an electrolyte at which co- 

 agulation actually begins can not of course be determined with 

 great precision. Moreover, its experimental value depends on 

 the exactness of the method of measurement. In the present 

 investigation the method employed is a rather rough one, there- 

 fore the values found can only be approximate. Yet they may 

 serve as the basis of a broad comparison. 



In Table 12 the electrolytes are classified according to the 

 magnitude of the concentration under consideration. 



In the first column are placed the electrolytes whose co- 

 agulative power is very slight, since they fail to cause even in- 

 cipient coagulation at the comparatively high concentration of 

 —- normal. They are all electrolytes with monovalent anions. 

 The organic acids included are indeed dibasic, but they are all 

 so weak that their dissociation hardly proceeds beyond the first 

 stage, and if the free divalent anion be present at all it must 

 be in such a minute quantity that they do not affect the colloidal 

 solution in any noticeable degree. 



In the second column are contained only two halides, 

 potassium chloride and iodide. It is a rather curious, fact that 

 the coagulative power of the bromide is so weak and does not 

 lie between those of the two halides. To exclude any mistake 

 the measurements were repeated, but with the same result. 



