ALUMINIUM HYDROXIDE BY ELECTROLYTES. 21 



be dissociated to such an extent that the trivalent anion PO/" 

 exists in any significant concentration ; but in the solution of 

 trisodium phos23hate this must undoubtedly be the case. 



In the last class, whose members have such a strong action 

 on the colloid that they produce incipient coagulation at a con- 

 centration below j^y^ equivalent normal, there is only one elec- 

 trolyte with monovalent anion, viz., picric acid. Of the anions 

 of the remaining eleven electrolytes, six are divalent, three are 

 trivalent, one is tetravalent and one may be hexavalent. 



According to Schulze, the coagulative power of an elec- 

 trolyte is chiefly determined by the valency of its ions. On the 

 whole, this rule holds in the present case, though there are 

 several notew^orthy exceptions. The other chemical and physical 

 properties of the anion seem to exercise considerable influence 

 on the coagulative power. 



When we take the lowest concentration of the electrolytes 

 necessary for complete coagulation as the basis of comparison, 

 we get the results shown in Table 13. 



This mode of comparison comes nearer to the njethods em- 

 ployed by former investigators, particularly Schulze and Freund- 

 lich, because what they measured may also be looked upon as 

 the lowest concentrations of complete coagulation. 



Among fifteen electrolytes which require greater concentra- 

 tions than -7^ equivalent normal, there is only one whose anion 

 is polyvalent, i. e. phosphoric acid. 



In the next column are found five electrolytes with mono- 

 valent anions, the remaining four having divalent ones. In the 

 third column are placed nine electrolytes with divalent anions 

 and five electrolytes with trivalent anions. In the last column 



