1887.] Bismuth on the ductility of Silver. 129 



coinage bars subjected to the regular procedure for the manufacture of 

 rupees in the Calcutta Mint. The experiments made in this connection 

 were fourteen in number. The bars used here for coinage weigh about 

 253 troy ozs. and are about 20 inches long, 225 broad, and 1 inch thick ; 

 they are cast in vertical iron moulds. In lamination they are first re- 

 duced by 11 pinches to a thickness of 0"23 in.; they are then annealed 

 and finally reduced by 12 additional pinches to a thickness of 0*06 inch. 

 A number of bars, poured from a pot of which the contents had proved 

 on assay of a granulated sample to be 916"6 fine, were selected for the 

 experiments, and as a preliminary step one of the bars was laminated 

 to test its ductility. It rolled out with smooth " wire " edges, and in- 

 deed its ductility was beyond suspicion as it resulted from a melting of good 

 coins. Another bar of the same batch was now melted and 1 per mille 

 of bismuth added to it, the result of the addition being checked, in this 

 and all following cases, by the assay of a granulated sample of the 

 metal, taken after thorough stirring. At the 8th pinch both edges of 

 the lower half of this bar began to crack, and at the 11th pinch these 

 cracks extended towards the middle line of the strap for about a quarter 

 of an inch, and occurred at about every half inch of the edge. After 

 annealing, and in the subsequent lamination to a thickness of 0"065 inch, 

 these cracks increased considerably in number, but did not become 

 sensibly deeper. The strap as finished was pronounced unfit for coin- 

 age purposes ; for although two blanks could have been cut from its 

 width, the edges were too jagged to admit of the blanks being obtained 

 exactly along the line from which it was desired to cut them — this posi- 

 tion being attained by means of a fixed lateral guide against which the 

 edge of the strap had to be maintained in cutting. With 2 per mille 

 of bismuth the results obtained on rolling were not much worse than 

 with 1 per mille. But the side cracks opened out more, and here again 

 it was noticed that the lower portion of the bar (upper and lower here 

 having reference to the casting in upright moulds) was somewhat less 

 ductile than the upper part. 



With 3 per mille of bismuth (fineness on assay 913'8) the bar 

 began to crack on both edges at the 9fch pinch ; at the 11th pinch there 

 were many cracks quite a quarter of an inch deep, aud after annealing 

 the bar these cracks increased at every pinch, so that at the 21st pinch 

 the strap was cracked all along both edges very badly. It would only 

 have been possible to obtain one blank from the width of this strap. 



As it was perfectly clear that no further experiments were re- 

 quired with larger proportions of bismuth, the subsequent trials were 

 made on coinage bars containing 0*5 per mille, 0-25 per mille, and, by 

 dilution of the latter bars with standard silver, to oven half and a quarter 

 17 



