12^ J. Scully — On the Effects produced by small quantities of [No. 2, 



muth in silver be readily estimated with the despatch indispensable for 

 mint operations ? 



II. What is the smallest amount of bismuth in silver that will 

 render it unfit for coinage, when present in bars of the Indian standard 

 fineness of 916*6 ? And, what is the amount of bismuth that may be 

 tolerated in such bars without materially injuring their ductility ? 



III. How is silver bullion containing bismuth which may be 

 tendered to the Mint, to be dealt with, supposing that establishment 

 accepts any metal that is brittle ; and how is the presence of bismuth 

 in refined bars to be accounted for ? 



I. As the purity of the bismuth to be used in the experiments 

 now to be detailed was a matter of first importance, I may briefly men- 

 tion the steps taken to ensure the purity of the metal. Refined bis- 

 muth was dissolved in nitric acid, precipitated as basic nitrate by dilut- 

 ing largely with distilled water, the nitrate digested in solution of 

 caustic potash, and then well washed, dried, and reduced by heating 

 with charcoal in a clay cracible. A series of synthetical assays, made 

 by dissolving together pure silver and pure bismuth^ the latter in the 

 proportion of from 1 to 5 milliemes, showed that our ordinary process of 

 assay, under such conditions, gave unreliable results, there being a sur- 

 charge, or higher report than should have been obtained, which varied from 

 0*7 to 2' 7 mill, when the proportion of bismuth was from 3 to 5 milliemes. 

 A modification in our process of assay was evidently required if it were 

 to be used for determining the fineness of silver bullion containing bis- 

 muth ; and the necessary steps to this end were, after repeated experi- 

 ment, found to consist in adding the smallest possible amount of hydro- 

 chloric acid for the precipitation of the silver, and increasing the amount 

 of nitric acid in which it was first dissolved. We use ordinarily for the 

 precipitation of an assay pound of silver 5*4 cc. of hydrochloric acid of 

 sp. gr. 1075, but 2'5 cc. of acid of this strength suffices for the complete 

 precipitation of an assay pound of even fine silver ; so that we have here 

 at once a means of diminishing the tendency of any bismuth in the silver 

 to form insoluble oxy chloride. If in addition to diminishing the amount 

 of hydrochloric acid we added a considerable excess of nitric acid to the 

 solution (which acid would not in any way interfere with the silver 

 chloride formed), all risk of the partial formation of insoluble bismuth 

 salts seemed removed. This in fact has proved to be the case, and the 

 successfal modified process for the assay of silver containing bismuth is 

 as follows : — 



The assay pound of silver bullion containing bismuth is dissolved in 

 6'5 cc. of nitric acid, sp. gr. 1200, with the aid of heat, about 5 ounces of 

 •water are added and then 10 cc. of nitric acid sp. gr. 1320. The silver 



