Van Name — Sulphocyanides of Copper and Silver. 451 



Aet. XLIY. — The Sulphocyanides of Copper and Silver in 

 Gravimetric Analysis ; by R. G. Van Name. 



[Contributions from the Kent Chemical Laboratory of Yale University — XCIX.] 



Cuprous Sulphocyanide. 



As early as 1854 attention was drawn by Rivot* to the pos- 

 sibility of estimating copper gravimetrically by weighing as 

 cuprous sulphocyanide, and to the advantages which the process 

 afforded in separating copper from other metals. Rivot's 

 method of procedure consisted in dissolving the substance to 

 be analyzed in hydrochloric acid, reducing the copper with 

 hypophosphorous or sulphurous acid, and precipitating with 

 potassium sulphocyanide. The precipitate dried at a moderate 

 temperature was weighed as cuprous sulphocyanide and then 

 as a control converted by ignition with sulphur into cuprous 

 sulphide and weighed in that condition. 



In his well known work upon quantitative analysis Fresenius 

 in one placef denies the practicability of the direct weighing 

 of copper as cuprous sulphocyanide on account of the tendency 

 of the latter to hold water even when heated to the tempera- 

 ture of incipient decomposition. As authority for this state- 

 ment he cites Claus,;}: who found 3 per cent of water in the 

 precipitate after drying at 115°, and Meitzendorfl, who gave 

 the percentage of water under the same conditions as 1"54. 



On a later page of the same volume,§ however, Fresenius, 

 after a trial of the process which gave 99*66 per cent of the 

 theory for copper, concludes that the method is practicable 

 although apt to give low results, particularly in the presence 

 of free acid. 



The process was again recommended in 1878 by BusseJ who 

 had employed it for the estimation of copper, both alone and 

 in the presence of iron, nickel, zinc and arsenic, obtaining 

 results very near the theory and plainly comparable with the 

 figures obtained by afterwards igniting the cuprous sulpho- 

 cyanide with sulphur in hydrogen. 



In spite of the evident advantages for certain purposes of 

 Rivot's method over other modes of determining copper, it has 

 never come into general use. The chief reason for this has 

 apparently been the difficulty and inaccuracy attendant upon 

 the weighing of the precipitate upon dried paper filters, a 

 process which can hardly be depended upon unless managed 

 yrith extreme care. 



* Comptes Rendus, xxxviii, 868. f Fresenius, 6th Aufl., i, 187. 



% L. Gmelin Handb., iv, 472. § 6th Aufl., i, 335. 



|j Zeitschr. Anal. Chem., xvii, 53. 



