378 i M. C. Lea — Transformations of 



2. The same quantity of silver oxide was triturated also for 

 20 minutes, in an agate mortar. As the abrasion is inappre- 

 ciable it was only necessary to dissolve out the unchanged 

 oxide with ammonia. There was left 



Metallic silver -0048 



showing the much less efficiency of the agate mortar. 



Mercuric Oxide. — The specimen taken was examined for 

 its solubility in cold dilute (one-tenth) hydrochloric acid, in 

 which it dissolved slowly but completely. 



Half a gram was taken and after trituration the unchanged 

 oxide was dissolved out by repeated digestions with hydro- 

 chloric acid. There remained mercurous chloride, a trace of 

 metallic mercury, and as a porcelain mortar was used, abraded 

 porcelain. The reduction products were dissolved out by a 

 lew drops of aqua regia, were filtered and precipitated by 

 hydrogen sulphide. 



Mercuric sulphide obtained -0354 



Corresponding to Hg -0305 



And to mercuric oxide "0329 



This therefore (disregarding the traces of metallic mercury), is 

 the amount of mercuric oxide which underwent reduction to 

 mercurous oxide. 



The oxidation of mercury to mercurous oxide and that of 

 mercurous to mercuric are both exothermic reactions. As re- 

 spects the thermic equivalent of the oxidation of mercury to 

 both its oxides, quite different numbers have been found by 

 different chemists. Nevertheless if from these different num- 

 bers we calculate the amount of heat disengaged by the com- 

 bination of Hg„0 with O we get almost exactly the same figures 

 whether we use Thomsen's results as modified by Nernst, or 

 those of the French chemists ; it matters little therefore which 

 are taken. Ditte in his work " Les Metaux " (Fascicule II, p. 

 500) adopts the numbers 21*1 and 15'5 respectively. 



On this basis, the amount of energy that must be supplied to 

 convert 2HgO to Hg 2 + (endothermic) is that which cor- 

 responds to 9*9 great calories. Therefore 400 grams of mer- 

 cury existing in the state of mercuric oxide will require that 

 amount of energy supplied to reduce it to mercurous oxide. 

 One gram therefore will require the equivalent of 24'75 small 

 calories and one milligram, '02475. 



In the experiment described mercurous oxide corresponding 

 to 30*5 mgs. metallic mercury was obtained. The energy 

 required to reduce 30*5 mgs. existing as mercuric oxide to 

 mercurous corresponds to 0*755 water gram degrees and this 

 again to 321-5874 gram meters. This number therefore, 322 



