.SaS Contrilut'wn towards the assaying of Coins. 



I effected the separation of the lead in another manner,- 

 I distilled the nitric solution in a retort till it was almost 

 reduced to a drv mass, softened the mass again with diluted 

 sulphuric acid, bv which means the sulphate of lead was 

 collected as a ponderous powder; after which I reduced it 

 to metallic lead. 



4th.- The last method afforded me at the same time the 

 ineans of detecting the small quantity of iron contained in 

 some of these coins, as this metal, when the thickened mass 

 was softened by diluted sulphuric acid, remained behind, as 

 ,an insoluble calx of iron, along with the sulphate of leady 

 •which appeared coloured by the iron of a yellow ochre co- 

 lour. By digestion in muriatic acid, the sulphate of lead 

 was freed from this calx of iron, and the latter was^ preci- 

 pitated from the' solution by prussiate of potash or by caustic 

 ammonia. 



3th. Nothing now remained in regard to the Greek coins 

 but the separation of the copper, which I effected with most 

 convenience by precipitating with polished plates of iron. 

 The difficuhy which attends the process of precipitating, 

 copper in a metallic form from a nitric solution by means 

 of iron or zinc, as a part of oxidated metal is thrown down 

 at the same time, did not occur in this case, as in the pre- 

 sent solution of copper the nitric acid was combined with 

 muriatic and sulphuric salts. 



Cth. 'Ihc Roman coins may be divided into two kinds, 

 the red and the yellow. The red consists of unmixed cop- 

 per, in the examination of which nothing further was to be 

 observed j in the yello-\\', however, the copper was mixed 

 w^ith a considerable quantity of zinc. 



In order to find out a complete' and accurate method of 

 separating the zinc I prepared a nitric solution of three 

 parts of copper and one part of zinc, divided it into four' 

 portions, and employed it for the four following experi- 

 ments : 



Exp. I. I decomposed one portion with sulphate of soda, 

 and precipitated tlic copper from it by iron . after the cop- 

 per was separated, I evaporated the solution to a dry mass 

 and drove off nitric acid from it several times, till the calx 

 (Tf iron was perl'ectly insoluble. I then precipitated the tin 

 from the solution freed from the iron by means of potash, 

 and estimated the quantity by counter-experiments, accord- 

 ing to which 1 00 parts of calx of tin gave 1 75 parts of dried, 

 or 123 parts of ignited, precipitated cak of tin. 



Erp. II. From the second portion I obtained the tin in 

 the following manner : — When the copper was separated 



and 



