S. L. Penfield — Sulphostannate of Silver from Bolivia. 453 



of the latter removed by evaporation. The residue after 

 moistening with nitric acid was digested with boiling water for 

 some time and the insoluble meta-stannic acid filtered off. 

 This was transferred while still moist to a beaker and treated 

 with strong ammonia into which hydrogen sulphide was con- 

 ducted until the meta-stannic acid had gone into solution. A 

 slight insoluble residue was filtered off at this point which 

 contained about 0*10 per cent of tin and 0*40 per cent of silver. 

 From the ammonium sulphide solution the tin was precipi- 

 tated by addition of a little sulphuric acid and weighed as 

 oxide. The filtrate from the stannic sulphide was evaporated 

 and yielded a little germanium which had not been separated 

 from the tin by the nitric acid treatment. In the original fil- 

 trate from the meta-stannic acid silver was precipitated by 

 means of hydrochloric acid and weighed as chloride. The 

 sulphur was next precipitated by barium nitrate, and after 

 purifying by fusion with sodium carbonate weighed as barium 

 sulphate. Before evaporating the filtrates hydrochloric acid 

 and barium were removed by precipitation with silver nitrate 

 and sulphuric acid. The excess of silver was finally removed 

 by ammonium thiocyanate and the germanium obtained from 

 the filtrate as described in a previous communication.* The 

 results of the analysis are as follows : 



Theory for Ag s (SnGe)S 6 

 Ratio. where Sn: Ge = 12 : 5. 



S 16-22 -507 5-92 16'56 



Sn 6-94 -0589) VIS 



Ge 1-82 -0253 \ ° 842 ° 98 1-83 



Ag 74-10 -686 8-00 74-43 



ZnandFe -21 



99-29 100-00 



In this compound tin is undoubtedly isomorphous with ger- 

 manium, and the two are present in about the proportion 12 : 5. 

 The ratio of S:Sn-fGe:Ag in the analysis is very close to 

 6:1:8, indicating that the formula is Ag 8 (SnGe)S 6 or 4Ag 2 S . 

 (Sn . Ge)S 2 . The agreement between the theory and the 

 analysis is satisfactory. 



The only sulpho stannates thus far known to occur in nature 

 are the rare species stannite, Cu 2 S, FeS, SnS 2 , franckeite, 

 5PbS, Sb 2 S 3 , 2SnS 2 and plumbostannite a mineral of doubtful 

 composition containing Pb . Fe . Sb . and S, described by Rai- 

 mondi.f Franckeite has recently been described by Stelzner^: 

 and in it Winkler was able to identify a small amount of ger- 



* This Journal, xlvi, p. 111. 1893. 

 fZeitsehr. Krvst., vi, p. 632, 1882. 

 % Jahrb. Min.*1893, II, p. 114. 



