1887.] Bismuth on the ductility of Silver. 127 



experiment was always remelted and tried at least a second time. The 

 number of experiments in this series amounted to fifty-three, and the 

 following is a summary of the results obtained. 



Fine silver when alloyed with only 1 per mille (one thousandth 

 part of its weight) of bismuth, and the casting rapidly cooled by 

 plunging it into water as soon as it has set, has its ductility, as tested 

 by lamination, sensibly but slightly impaired, the straps resulting from 

 rolling having slightly jagged edges. When the proportion of bismuth 

 is increased to 2, 3, 4 and 5 per mille, the plan of cooling remaining the 

 same, the raggedness of the edges of the straps was somewhat increased 

 but not very markedly. If, however, the casting was allowed to cool 

 down completely, but very slowly, in contact either with the mould or a 

 stone floor, the results were very different. Under this condition of 

 cooling, a bar composed of fine silver with 4 per mille of bismuth was 

 completely brittle ; it was readily broken and its fracture was strongly 

 crystalline. On laminating it, small cracks appeared all over the sur- 

 face on the second pinch, the bar emitting a crackling sound under the 

 rolls, much like the " cry " of tin, and on the 4th pinch the bar cracked 

 deeply at the edges. This remarkable effect on the molecular structure 

 of this alloy of silver and bismuth, as due solely to the mode of cooling 

 the casting, was repeatedly verified on the same metal by remelting and 

 cooling rapidly and slowly alternately. The case seems analogous to 

 that of bronze, where slow cooling of the alloy after casting is said to 

 make it hard and brittle. 



Fine silver with 6 per mille of bismuth, rapidly cooled, was dis- 

 tinctly cold-short and crystalline on fracture ; the bar cracked on the 

 surface at the 4th pinch. With 7 per mille of bismuth these evidences 

 of diminishad ductility were slightly more pronounced. With 8 per 

 mille of bismuth the silver was still more brittle, the bar broke readily 

 when hammered, and cracked all over the surface on the 4th pinch from 

 the rolls. With 9, 10 and 11 per mille of bismuth, the bar of silver 

 could be readily broken in two by merely striking it against the edge of 

 an anvil, the fracture was coarsely crystalline, and the bar, in one case, 

 proved to be very red-short, a mere tap from the tongs sufficing to 

 break it in two when heated for the purpose of annealing. Although 

 these bars were so very brittle, it was still possible to roll them into 

 thin straps after careful annealing ; but the edges of the straps so pro- 

 duced were deeply jagged and indented by cracks. These bars also all 

 emitted the peculiar crackling noise under the rolls which has before 

 been mentioned. 



An alloy containing 990 parts of silver and 10 of copper then had 

 added to it successively 1, 2, 3, 4, and 5 per mille of bismuth, the cast- 



