CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



THE DECOMPOSITION OF MERCUROUS CHLORIDE BY 

 DISSOLVED CHLORIDES: A CONTRIBUTION TO THE 

 STUDY OF CONCENTRATED SOLUTIONS. 



By Theodore William Richards and Ebenezer Henry Archibald. 



Received November 23, 1901. Presented December 11, 1901. 



Introduction. 



Long ago Miahle observed that a concentrated solution of common 

 salt acts upon calomel with the formation of small amounts of mercuric 

 chloride.* Many years afterwards, one of us,f without knowing of his 

 work, rediscovered this reaction, and found that the fluctuations in the 

 potential of the " normal calomel electrode " of Ostwald, are due to ita 

 disturbing influence. At that time it was shown that the reaction is 

 much diminished by dilution, and hence that a decinormal solution is far 

 better as an electrolyte than a normal solution. The "decinormal 

 electrode," thus recommended for the first time, has since come into 

 common use. 



It was shown also that neither light nor oxygen are important causes 

 in effecting the decomposition, but that the reaction is much furthered by 

 increase of temperature. No attempt was made at the time to fathom 

 the matter, but a suggestion was made that the reaction might be due to 

 the catalytic action of the ionized chlorine of the dissolved chloride. 



The investigation of the problem which was at that time promised has 

 now been continued, and the object of this paper is to show that while the 

 second condition of this suggestion seems probable, the first does not hold. 

 Another example is thus afforded of the frequently recurring circum- 

 stance of the removal of a reaction from its classification among catalytic 

 phenomena after better acquaintance with its nature. 



* Miahle, J. Pharm., 26, 108; Ann. Cliim. et Phys. (3), 5, 177 (1842). 

 t Richards, These Proc, 33, 1 (1897) ; Z. phys. Ch., 24, 39. 



