1887.] Bismuth on the ductility of Silver. 131 



and with copper, so as to reduce the proportion of bismuth in the coin- 

 age bars to less than 0'5 per mille ; and thus neutralize its injurious 

 effects on the ductility of the bars. 



The explanation of small quantities of bismuth being found in re- 

 fined silver, i. e., silver which has undergone parting for the extraction 

 of the gold which was contained in it, seems sufficiently indicated in the 

 following extract from Dr. Percy's work (Silver and Gold, Part I, 

 p. 474), where that author is referring to the experience of Dr. Rossler in 

 parting silver : " Bismuth has been found in nearly all kinds of silver ; 

 but in parting by sulphuric acid it is lost partly in the fine silver and 

 partly in the slags." The italics are mine. That small quantities of 

 bismuth adhere very tenaciously to silver, when once mixed with that 

 metal by melting, is shown by the following experience. A quantity of 

 silver containing bismuth, which had accumulated from the laboratory 

 experiments before detailed, was melted, granulated, dissolved in nitric 

 acid, and the silver precipitated as chloride. The silver chloride, after 

 repeated washings, was reduced by heating in a plumbago pot with 

 chalk and charcoal. The resulting ingots, on assay, showed at once that 

 bismuth was still present in them in very appreciable quantity. 



It may here be of interest to mention that I have found about 0*7 

 per mille of bismuth in some old Hindu punched coins, forming part of 

 of a treasure trove which was found at Chaibassa, in the Singhbhum 

 District. 



The following is a summary of the main results detailed in this 

 paper : — 



1. The Indian assay process for silver bullion is, incidentally, a 

 delicate qualitative test for the presence of bismuth in such bullion. 



2. The assay process can be readily modified so as to give accurate 

 results in the presence of such proportions of bismuth as are likely to 

 be encountered in practice. 



3. Fine silver when alloyed with only 1 per mille of bismuth has 

 its ductility sensibly impaired thereby ; and 1 per cent, of bismuth is 

 sufficient to render fine silver, or alloys of it with copper down to 906 

 fine, extremely brittle. 



4. Eine silver alloyed with small quantities of bismuth, and silver- 

 copper alloys down to 980 fine when containing small proportions of 

 bismuth, have the remarkable property of being more ductile when 

 rapidly cooled in water after casting than if allowed to cool very slowly, 

 thus resembling bronze in this respect. 



5. Coinage bars such as are used in the Calcutta Mint, and with 

 the procedure there adopted for rolling, are quite unfit for coinage 



