2B ART. 8. — S. KAWAMURA : COAGULATION OF COLLOIDAL 



most interesting fact of all is that the coagulative power of 

 fumaric acid is so well developed while the stereoisomeric maleic 

 acid is quite inactive. The dissociation constant of maleic acid 

 considered as a monobasic acid is indeed far greater than that 

 of fumaric acid, being 0.00117 as against 0.000093 ; but in the 

 dissociation constant^ with respect to the second hydrogen ion 

 the relation is reversed, being only 0.00000039 for maleic acid 

 and 0.000018 for fumaric acid. These latter constant were found 

 for 100°. At 25° their values may be somewhat different, yet 

 the order of magnitude will remain nearly the same. This 

 explains w^hy the dissociation constant as monobasic acid cal- 

 culated from the electrolytic conductivity remains very nearly 

 constant for maleic acid, while it increases, though at first very 

 gradually, with increasing dilution for fumaric acid. Hence the 

 concentration of the divalent anion must be very much greater 

 in the solution of fumaric acid than in that of maleic acid. 

 This accounts for the great difference in the coagulative power 

 of the two acids. 



The coagulative power of tartaric acid has been found to be 

 markedly greater than that of fumaric acid ; this may be looked 

 upon as the consequence of the greater dissociation constant of 

 the second hydrogen ion for this acid, the constant being 0.000059 

 or more than three times larger than that of fumaric acid. 

 This doubtless also applies to oxalic acid. 



The indifferent organic substances, ethyl alcohol, phenol and 

 mannite, were tested, and found to lack coagulative power, at 

 least in not too high concentrations. Such is doubtless the case 



1. W. A. Smith : Zeits. für physik. Chem., 25, (1898), 241. 



