46 Assistant- Prof. J. W. Clark on certain Cases 



through the fused mercuric chloride for some time, the appa- 

 ratus was allowed to cool ; and its contents were subsequently 



Fig. 2. 



J.W.CLARK DEL 



pulverized and exhausted with water, which left an insoluble 

 residue of mercurous chloride (Hg 2 Cl 2 ), which was not entirely 

 confined to the inside of the — porous pot. 



Mercurous chloride dissolves in fused mercuric chloride, 

 probably giving rise to a mercuroso-mercuric chloride of 

 analogous composition to some of the well-known double 

 chlorides which mercuric chloride forms. The want of time 

 consequent upon the completion of an investigation on the 

 influence of pressure on electrolytic conduction, upon which I 

 have long been engaged, has prevented my examining this point. 



The conduction of mercuric chloride is electrolytic, giving rise 

 to chlorine and mercurous chloride; and there seems no reason 

 to doubt that it conforms quantitatively to Faraday's Law ; 

 but the volatility of this substance, as also in the case of 

 mercuric iodide, and of ihe products of their decomposition, 

 would render its further proof difficult. 



The causes rendering its electrolytic decomposition difficult 

 may be summed up as follows : — 



(1) The volatility of mercurous chloride and its solubility in 

 mercuric chloride. 



(2) The near melting- (265° C.) and boiling- (295° C.) 

 points and great volatility of mercuric chloride facilitate the 

 mixing and recombination of the products of its decomposition, 

 and the vapour renders the detection of chlorine by the ordinary 

 test difficult. 



(3) As previously stated in reference to mercuric iodide, 

 it is possible that the volatility of these substances is con- 

 nected with a high diffusive rate, ivhen fused, which icoidd 



facilitate the recombination of the products of its electrolytic 

 decomposition. 



(4) The electrical resistance of the fused substance is much 

 higher than that of the mercuric iodide. 



Before concluding this paper, I wish briefly to refer to the 

 properties of fused mercuric iodide and chloride with refer- 

 ence to the porous battery-pots in which the electrodes were 



