MERCURIC SALTS CHANGE INTO EACH OTHER. 1 §9 



is not sensibly oxidised by the air at temperatures as high as 100° at 

 least, it is readily oxidised at 150°. Heated for six hours with water, 

 in an atmosphere of carbon dioxide in the tube, it underwent hardly 

 any change, a very little mercury and mercuric chloride only being 

 formed. Dissociation did not progress because of the retention of the 

 mercury vapour. In other experiments I used, in one case, a 3.7 per 

 cent, solution of hydrochloric acid instead of water merely, nnd in 

 another case, a 6.5 per cent, solution of potassium chloride. Here the 

 presence of the acid or of the potassium chloride caused a small amount 

 of dissociation into mercury and mercuric salt, showing that at this 

 temperature, mercurous chloride approaches the iodide in its readiness 

 to drop mercury in presence of the potassium salt. Very different 

 w r ere the results when the air of the tube had been displaced by oxygen 

 before sealing. There was still only very little metallic mercury 

 observed, but there was now much mercuric salt obtained. When 

 water alone w r as used and the heating had lasted six hours, the mercuric 

 chloride w 7 as found partly in solution, and partly as brilliant micaceous 

 scales, brown in colour, of oxychloride. When the water contained 

 hydrochloric acid in one case and potassium chloride in another case, 

 in the proportions given above, all the mercuric salt was found in the 

 solution. In all cases there had been large absorption of the oxygen. 

 In presence of hydrochloric acid, so much as -17.5 per cent, of the 

 mercurous chloride (one gram) became mercuric chloride ; in the 

 potassium chloride solution the conversion was much less though still 

 considerable, it having extended to 19 per cent, of the mercurous 

 chloride. In this case, too, the solution was very alkaline. In 

 another experiment where 50cc of the 3.7 per cent, hydrochloric acid 

 were taken and the time of heating was extended to ten hours, even 

 60 per cent, of the mercurous chloride (one gram) changed into mer- 

 curic chloride. The superior efficiency of hydrochloric acid over potas- 



