1887.] Bismuth on the ductility of Silver. 133 



molten metal to the oxidising action of the air, aided in some cases by 

 the use of nitre. This may seem at variance with our experience here, 

 but is probably not so after all. The brittle bullion treated in Japan 

 evidently contained a considerable amount of base metal in addition to the 

 bismuth ; the slags formed in the early stages of the melting consisting 

 chiefly of litharge, &c. What we had to deal with was refined silver 

 990 fine, and in this case of coarse it would be more difficult to free the 

 bullion from bismuth than if lead and other base metals were present in 

 sufficient quantity to form a copious slag. But in any case (without, 

 however, venturing to give any authoritative opinion on the subject) I 

 ■doubt whether the Indian Mints would willingly undertake any con- 

 siderable refining operations on bullion. The conditions under which 

 these Mints receive bullion are very different from those obtaining in 

 the case of the American and Australian Mints, and the Imperial Mint 

 of Japan. In those countries encouragement has to be given to native 

 mining industries, and hence a good deal of work in the way of 

 purification and separation of metals is undertaken by their mints. 

 In India practically all the bullion is imported by banks and merchants, 

 from Europe, America, and elsewhere, and tendered to the Mints for 

 coinage at a fixed charge. The Indian Mints may therefore, as in the 

 case of the Royal Mint in London, very properly require that all 

 l)ullion tendered to them shall be free from taint of brittleness, and 

 so far fit for coinage. It is for the importers to make sure that their 

 purchases are satisfactory in this respect. 



As to the amount of bismuth that will render silver brittle, my re- 

 sults seem to be substantially in accord with those of Messrs. Gowland 

 and Koga. They found that pure silver alloyed with only 5 per mille 

 of bismuth was very brittle ; the casting, I suspect, was allowed to cool 

 slowly. Coinage bars of 900 fine, containing nearly 14 per mille of 

 bismuth, were brittle and altogether unfit for coinags, as I should have 

 expected. But by special treatment in the way of repeated annealings, 

 some of these bars were rolled down successfully without cracking, al- 

 though they still could not be used for coinage. 



In the other matters treated of in my paper the results obtained will 

 supplement those of my confreres in Japan. 



