356 PROCEEDINGS OP THE AMERICAN ACADEMY. 



It remains now to detect the mechanism of the reaction. The work 

 of Le Blanc and Noyes led them to believe that in dilute solutions con- 

 taining an excess of the soluble electrolyte the new ion is bivalent, being 

 formed by the reaction 2 CI' + HgCL — HgC^". It will be shown that 

 our own evidence supports this conclusion also. 



The reaction with which we are concerned may perhaps be written 

 thus : — 



xHCl ±; xH- + xCr 



+ 

 Hg^Cla U HgCla + Ilg 



l-f li 14' 



Solid Hg^Cl2 HgCl(o^x) Liquid mercury 



The ion HgCl(2+i) will of course be the bearer of x negative charges of 

 electricity. The above expression does not attempt completeness, but 

 strives merely to represent the most essential features of the reaction in 

 the simplest possible form. 



The first conclusion to be noted is that the concentration of the un- 

 combiued but dissolved mercuric chloride will be constant, since it is 

 formed by a reaction involving two precipitates. Hence the concentra- 

 tion of the ion HgCl,2+i) should vary as the concentration of the chlorine 

 ion raised to the xth power. 



It is immediately clear that x must be more than unity, for in the less 

 concentrated solutions the concentration of the mercury present increases 

 faster than that of the dissolving chloride, while the concentration of the 

 ionized chlorine is supposed to increase less rapidly than the latter. 



By taking x = 2 we obtain much more satisfactory agreement. If we 

 assume that the concentration of the ions present is proportional to the 

 specific conductivity,* we find that for solutions as far as twice normal the 

 calculated curve agrees almost precisely with the actual amounts of mer- 

 cury found. The specific conductivity of a twice normal solution of 

 hydrochloric acid is 0.505, while that of a normal solution is 0.295. 

 The squares of these numbers are respectively 0.255 and 0.087, two 

 values which are very nearly proportional to the weights 148 and 48 

 milligrams of mercury per litre which were actually found to be dis- 

 solved from calomel by twice normal and by normal solutions of hydro- 

 chloric acid respectively. 



With more concentrated solutions the results of this calculation agree 



* The possible dangers of this assumption are well known. It is made here 

 simply in default of more certain knowledge. 



