428 QUICKSILVKR DEPOSITS OF THE PACIFIC SLOPE. 



prevents the combination of free hydrogen and oxygen at low temperatures. 

 There is, liowever, notliing to indicate such anomalous resistances, and in 

 any event the considerations adduced demonstrate a tendencv to the forma- 

 tion of sodium sulphide. On the other hand, though manv efforts have 

 Ijeen made, neither Dr. Melville nor I have succeeded in devising an ex- 

 perimental method proving the presence of sodic sulphide, as such, in 

 solutions of this kind. If it does exist, of course mercuric sulphide nuist 

 immediately dissolve in the solution without the evolution of gas. 



The theoretical results given in the last paragraph were worked out 

 before a single one of the experiments described in this chapter was made, 

 and, in fact, formed the basis of the entire investigation. When the attempt 

 was made to dissolve mercuric sulphide in the mixture at the temperature 

 indicated, in open vessels, it was found to go into solution without evolution 

 of gas, thus behaving as if free sodic sulphide were present. This, however, 

 in view of the facts afterwards ascertained, does not prove the actual pres- 

 ence of free sodic sulphide. 



Formation of Na'S in the presence of HgS. WheU, lu additloU tO the tendenCV 



towards formation of sodic sulphide discussed above, the affinity of mercuric 

 sulphide for this compound is brought into play, it can be proved experi- 

 mentally that sodic sulphide is formed. We found that at a temperature of 

 about 90" a mixture of the two carbonates and the sul])hvdrate dissolves 

 mercuric sulphide freely without a sensible evolution of gas. If the solvent 

 does not contain sodic sulphide, it must contain the sulphydrate. Hence it 

 becomes important to ascertain the behavior of mercuric sulphide to so- 

 dium sulphydrate at moderately elevated temperatures. 



While sodic sulphydrate will not dissolve a trace of mercuric sulphide 

 at ordinarv" temperatures, if mercuric sulphide be added to a solution of so- 

 dium sulijlndrate which stands upon the water-bath, hydrogen sulphide is 

 evolved and mercuric sulphide goes into solution. The fixct that hydrogen 

 sulphide is evolved demonstrates that sodic protosulphide mu.st be formed. 

 Cooling does not reprecipitate the mercuric sulphide, and the compound dis- 

 solved is therefore of the form HgS, ;?Na''8. Though the solubility of mer- 

 curic sulphide in warm solutions of the alkaline sulphydrates at ordinary 

 pressures has, so far as I know, never been explicitly stated, I have no 



