RICHARDS AND ARCHIBALD. — CONCENTRATED SOLUTIONS. 355 



The shape of the first section of the curves, where the concentration of 

 the mercury present increases at a greater rate than does the correspond- 

 inw amount of electrolyte, suggests at first tliat the undissociated part of 

 the latter is the portion concerned in the reaction ; but the curve repre- 

 seutinnf a power of the concentration of the ionized chlorine has of course 

 a similar tendency. 



Hence the general shape of the curve is an insufficient basis for de- 

 cision between the two hypotheses. 



The fact that strong solutions of cadmic chloride have little or no 

 influence on mercurous chloride supports the latter of the two hypotheses, 

 since concentrated cadmic chloride solutions contain but a very small 

 concentration of ionized chlorine. 



More direct light upon the question is obtained by the measurement 

 of electrolytic conductivity. According to the first hypothesis, which 

 demands the presence of an undissociated double salt, the conductivity of 

 salt solution should be considerably decreased by the addition of mercuric 

 chloride. As a matter oE fact, we found that the dissolving of mercuric 

 chloride to saturation in a twice normal solution of common salt dimin- 

 ished but slightly the conductivity of the solution. The work of Le Blanc 

 and Noyes* furnishes similar results concerning hydrochloric acid; and 

 moreover these investigators showed by the catalysis of methyl acetate 

 that the concentration of the hydrogen ion was undiminished by the addi- 

 tion of mercuric chloride. Hence the new compound is to be considered 

 as highly ionized. 



Yet further evidence is to be obtained by referring to the specific con- 

 ductivities of strong solutions of the chlorides studied. f Here we find 

 that while the conductivities of solutions of sodic and baric chlorides 

 increase with the concentration as far as they may be followed, those of 

 calcic and hydric chlorides exhibit maxima at a concentration about six 

 times normal. The agreement between these maxima and those ex- 

 hibited by our own curves at seven times normal is close enough to 

 suggest an essential relation between the cause of conductivity and the 

 cause of Miahle's reaction. 



The evidence thus furnished is all consistent in indicating that the 

 nature of the reaction is the addition of HgCL to the chlorine ion, with 

 the formation of a complex ion. This conclusion agrees with that of Le 

 Blanc and Noyes, based upon other data. 



* Le Blanc and Noyes, Zeitschr. phys. Chem., 6, 389, seq. (1890). 



t See Kohlrausch and Holborn (1898), Leitvermiigen d . Electrol., pp. 145-154. 



