jgy S. HADA; HOW MERCUROUS AND 



the air, does dissolve very slowly as mercuric chloride when it is 

 exposed to the air under a layer of solution of an alkali chloride. 

 But any such effect of the air upon the very small quantity of mercury 

 liberated by dissociation from mercurous chloride in warm water must 

 be utterly inappreciable. 



Mercurous chloride not sensibly oxidised at lower temperatures. — I now 

 describe a repetition of Mialhe's experiments with the crucial modifi- 

 cation of using a current of carbon dioxide instead of one of air. Two 

 flasks holding equal quantities of water and equal quantities of mer- 

 curous chloride were kept together at about 50° for 45 hours, the one 

 flask containing air being closely corked, and the other fitted with 

 reflux condenser and a tube through which a current of carbon dioxide 

 was passing the whole time. The result was much more limited than 

 that obtained when mercurous nitrate was operated upon, the mercuric 

 chloride produced being exceedingly small in quantity. Had I used 

 strong solutions of alkali chloride instead of water, no doubt the 

 quantities of mercuric salt obtained would have been much larger and 

 been measurable. But, as it is, my results here and from experiments 

 upon the nitrate, entirely confirm Mialhé's, in so far as they show the 

 production of much more mercuric salt in a current of gas than in a 

 closed space. In the present experiment, the water from the flask 

 through which carbon dioxide had been passing gave a marked 

 blackening with hydrogen sulphide, while that which had been shut 

 up with the mercurous chloride and air gave only a moderate brown- 

 ing. At the same time, they prove that in his experiments the 

 exposure to the open air or to a current of air increased the production 

 of mercuric chloride so largely, not by an oxidising action, but by 

 carrying off mercury vapour, and thus favouring the progress of dis- 

 sociation. 



Oxidation of mercurous chloride at 150°. — While mercurous chloride 



