458 A. L. Day a?)d J. K. Clement — Gas Thermometer. 



by ammonia. The solution was allowed to stand and then 

 filtered from iron and alumina. The precipitation of the cop- 

 per was done very gradually with constant shaking to avoid 

 carrying down the impurities, and after long standing was fil- 

 tered. The filtrate was concentrated to a small volume in porce- 

 lain. A small additional precipitate which came down in this 

 process was worked over with care to avoid any possible loss 

 of impurities, especially lead, though no metal but copper was 

 found in it. The filtrate was then examined as usual. A 

 word is needed in reference to the presence of zinc. This was 

 found in every sample examined, in fact, it was generally the 

 chief impurity. It was suggested that this zinc or at least a 

 part of it might have come from the large flasks of Jena glass 

 in which the acid solutions of the copper stood. To test this 

 point, a sample of copper in which had been found '089 per 

 cent of zinc was tested again. In this determination Jena 

 glass was entirely discarded. The zinc found was "091 per 

 cent. As these results agree within the limits of error, it is 

 evident that Jena glass under these conditions will not con- 

 taminate solutions with zinc, at least in quantities of this order 

 of magnitude. For the determination of silicon in the copper, 

 25 grams were placed in a platinum basin, dissolved in nitric 

 and sulphur acids, and evaporated over a crown burner to white 

 fumes. The residue was dissolved and filtered. The filter 

 was burned and the small residue tested for silica by hydro- 

 fluoric and sulphuric acids. Since it was feared that some 

 silica might come from the watch glass used to cover the plat- 

 inum dish during this operation, a blank was carried out w T ith 

 the reagents under the same conditions. Within the limits of 

 error none was found. 



For the estimation of sulphur the method of Lobry de Bruyn* 

 was used, in which the copper is separated from the nitric acid 

 solution by electrolysis. Twenty-five grams of metal was 

 dissolved in 75 cc nitric acid diluted with about an equal quan- 

 tity of water, and then the excess of acid evaporated as far as 

 possible on the steam bath. The electrolysis was done in a 

 large platinum basin, which served as a cathode. The basin 

 was covered with a glass plate pierced to admit a cylindrical 

 platinum crucible which formed the anode. The current den- 

 sity was about *015 — After a time it was found neces- 



sq. cm. 



sary to pour off the solution from the precipitated copper and 

 remove the free acid by another evaporation. A repetition of 

 this operation is advisable. The filtrate from the copper is 

 evaporated to dryness in porcelain and the small residue of 

 nitrates decomposed by hydrochloric acid. The final residue 



*R des trav. Chim. de Pays Bas, x, 125, 1891. 



