MERCURIC SALTS CHANGE INTO EACH OTHER. 



173 



a cork, while the other was provided with a reflux condenser and a 

 tube to lead carbon dioxide through the solution. The flasks were 

 placed side by side in an oven and were kept there for about 45 hours 

 at a temperature of 45-47°, while carbon dioxide was continuously 

 bubbled through the solution and precipitate in one of the flasks. On 

 examination, the contents of the flask containing air enclosed gave 



I OD 



0.0040 gram mercuric sulphide and those of the flask kept all the 

 time in a continually renewed atmosphere devoid of oxygen gave 

 0.0107 gram mercuric sulphide or 2 J times more than the other. 

 Had the current of gas been one of air it might have been supposed to 

 have caused oxidation, but, as the experiment was conducted, the 

 effect could only be due to the carrying off of mercury vapour by the 

 current of chemically inactive gas. 



The experiment was repeated, using in each flask 2 grams mer- 

 curous nitrate, 20cc. water, and a little dilute nitric acid. The tem- 

 perature was 45-50° and the time w r as extended to 75 hours. The 

 result was : mercuric sulphide obtained from the closed flask 0.0082 

 gram ; from the flask through which carbon dioxide had streamed, 

 0.028 gram, or nearly oh times as much. 



A similar experiment performed at a little lower temperature, 

 20-30° and lasting 50 hours gave quantities of mercuric sulphide too 

 small to weigh, but the blackening by hydrogen sulphide of the mother- 

 liquor of the precipitate caused by sodium chloride was far stronger 

 where carbon dioxide had been passed all the time than where the 

 solution had been corked up with the air in the flask. 



Mercurous nitrate changed by heat to mercuric salt by reduction of 

 nitric acid. — -In a sealed tube and in an atmosphere of carbon dioxide, 

 mercurous nitrate dissolved in one per cent, nitric acid, one gram in 

 lOcc, kept at 150° for five hours, is largely converted into mercuric 

 salt by some of the nitric acid being reduced to nitrous acid. The 



