CXIII.—The system silver–silver sulphide
Journal of the Chemical Society Transactions
1851 Exhibition Scholar). PERCY, in his ( ( Metallurgy of Gold and Silver " (Part I., page 25), gives the resulh of some experiments, made in his laboratory, on the question of the solubility of silver sulphide in silver. He states that he found that if equal weights of silver and silver sulphide are melted together, the mixture on cooling separates into two layers, one being silver sulphide and the other silver contraining approximately 18 per cent. of silver sulphide: also, on re-melting the
... on re-melting the layer rich in silver, no further separation occurs. According t o Abegg ((' Handbuch der Anorganischen Ghemie," 2, 707), however, silver sulphide can be melted in all proportions with silver, forming a homogeneous mixture. Pelabon (Compt. rend., 1906, 143, 294) has, to some extent, investigated the equilibrium between silver and sulphur. He found that the freezingpoint curve stops at the melting point of silver sulphide, that composition corresponding with the maximum amount of sulphur which silver can absorb. He gives the melting point of the sulphide as 825O. Further, he states that there is a eutectic formed, melting a t 800° and having a composition very near to that of silver sulphide. It seemed of interest, therefore, to investigate the system as thoroughly as possible, since the information a t present obtainable on the subject is somewhat conflicting. Abegg mentions the existence of a sub-sulphide, Ag,S, and it was hoped that some indication of the existence of this compound in solution might be obtained. This system has some technical interest, since in recovering silver from residues containing thiocyanate, trouble is caused by the presence of sulphur in the metal obtained. The presence of sulphur is readily explained by the results of an experiment made by the author. Seven grams of silver thiocyanate wore heated to about 1000° with 50 grams of silver. If all the sulphur present had been converted into sulphide, then the silver would have taken up 18 per cent. Actually, it was found that the metal contained 12 per cent. Supposing the thiocyanate to decompose in the generally accepted manner, according to the equation: 8AgCNS = 4Ag2S + 2CS2 + 3(CN), + N" the sulphide formed would correspond with the presence of about 9.5 per cent. Evidently some of the carbon disulphide farmed reacts with the silver a t the high temperature of the experiment.