430 QUICKSILVER DEPOSITS OF TOE PACIFIC SLOPE. 



of the solution to 0.29 gram per liter. Then the liquid began to grow 

 darker and the color deepened, until the entire quantity of sulphide pres- 

 ent was about 0.12 gram per liter. The precipitated material was so finely 

 divided that it would not settle and could not be filtered out, and it was 

 therefore impossible to say where, if at all, the precipitating effect of water 

 ceases. Similar experiments yielding analogous but not numerically iden- 

 tical results were made with other solutions. 



The cause of this precipitation is clear. It is known through the in- 

 vestigation of Messrs. Kolbe, Thomsen, and others that, while in moderately 

 concentrated solutions NaHS + NaHO = Na'"S-)-H-0, this reaction is par- 

 tially reversed on dilution, or that in the presence of much water sodic 

 sulphide is decomposed by water, the jiroportion of the sulphide under- 

 going this decomposition increasing gradually witli the dilution. It is evi- 

 dent that the decomposition of HgS, nNa'S is effected in the same way, 

 more and more of the protosulphide in combination being converted into 

 the sulphydrate as the dilution increases, probably without any hunt. Since 

 mercuric sulphide decomposes hot sodic sulphydrate, the effect of dilution in 

 hot solvents will evidently be less than in cold ones. 



Brunner found that dilution of solutions of such a salt precipitated a 

 black mass, in which, on examination with the lens, minute globules of 

 mercury were visible. The quantity of niercur}" was extremely small, so 

 that the precipitate, on analysis, corresponded very closely indeed to the 

 composition expressed by the formula HgS. Gmelin-Kraut' appear to 

 have some independent confirmatory evidence on this point. If metallic 

 mercury be precipitated in diluted solutions, of course sulpluir is liberated, 

 and, as shown above, alkaline hydrate nnist also be present. Now, when 

 these two substances are brought in contact, sodic hyposulphite forms 

 Accordingly Jh-uiuuM' found hyposulphite in solution forty years before 

 the decomposition of alkaline sulphide in dilute solution had been eluci- 

 dated. 



As Brunner experimented with IlgS, IvS, I thought it best to com- 

 pare the action of HgS, 4Na^S. A very concentrated, perfectly clear solu- 

 tion of fresldy prei)ared mercuric sulphide in a mixture of sodic sulphy- 



' Haailbiieli tier Clieniio, vol. 3, p. S.")I. 



