60 PROCEEDINGS OF THE AMERICAN ACADEMY 



copper, &c. is dissolved in hot concentrated sulphuric acid, and the 

 silver subsequently precipitated, by means of metallic copper, from a 

 somewhat diluted hot solution of the sulphate of silver thus obtained. 

 Since ordinary commercial sulphuric acid * is used in this operation, 

 it is not strange that a portion of the lead with which it is contami- 

 nated should be transferred to the silver. The lead salt is perhaps 

 reduced by the metallic copper in the manner so well described by 

 Odling, in liis memoir " On the Reciprocal Precipitations of the 

 Metals." t It is, moreover, not impossible that some sulphate of lead 

 may fall when the acid liquor is diluted, and become mixed with the 

 precipitated silver. It is not credible, however, that the lead in the 

 coin can have been derived from the copper used to form the standard 

 alloy, for this supposition would imply that copper of very inferior 

 quality had been employed. According to Ivarsten,J copper which 

 contains but one per cent of lead is utterly unfit for manufacturing 

 purposes, since it cannot be worked at any temperature. Now tlie 

 least amount of lead which we found in fifty cents' worth of American 

 silver is 0.0253 gram, in 10 half-dimes of 1853. These 10 half-dimes 

 contain 1.243 gram, of copper, and if tliis metal had been the source of 

 the lead, it must have contained more tlian two per cent of that impnrit}'. 

 We are ignorant of the process of preparing silver whicli was in 

 use at the British Mint in 181G. Perhaps the silver in the coin of 

 that date was obtained by cupellation, and it is well known that silver 

 so obtained almost always contains lead. § 



* D'Arcet, Jonrn. fiir tech. u. oekon. Ch., 1829, IV. 420. 



t Quar. Journ. Chem. Soc. of London, 1857, IX. 289. 



t In his System tier Metallurgie, (Berlin, 1832,) V. 245. 



§ Authorities differ as to the amount of lead contained in crude cui)elled silver 

 ("lightened silver," anjent e'clave, Blicksilber). According to Berthier (Essais par 

 la Voie Seche, (Paris, 1848,) II. 724), it contains, on an average, only 1 per cent 

 of lead. Kerl (Handbuch der metallurgischen Hiittenkunde, (Freiberg, 1855,) III. 

 152), on the other hand, says that it contains from 5 to 10 per cent of impurity ; 

 and according to Karsten (Sj'stem der Metallurgie, V. pp. 200, 201) Blicksilber 

 contains at least 12 per cent of lead, and often more, the proportion of lead to 

 silver being entirely dependent upon the temperature of the cupelling furnace. 

 Since such silver is unfit for use, it is refined by small portions, either by a second 

 cupellation at a high heat, or by melting it in crucibles with saltpetre and borax or 

 some other flux (Kerl, op. cit., III. pp. 181 to 198J; but it appears to be imprac- 

 ticable, or at least not advantageous in practice, to remove the last traces of lead 

 from the silver by either of these processes. (See Kerl, oj). cit., I. 224 ; or Plattncr, 

 Probirkunst mit dem Lchhrolire, (Leipzig, 1853,) p. 403). 



