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



of the lesser proportion just stated. Here the results were rather discor- 

 dant ; they appear to have been somewhat influenced by the state of 

 different rolls, and by quick or slow annealing. The general outcome 

 of the tests, however, was that although some of the straps, containing 

 the proportions given of bismuth, were jagged at the edges, and so would 

 have yielded a diminished percentage in outturn of good blanks, others 

 were not materially worse than the average of straps without any bis- 

 muth at all. As a result of this part of the enquiry, it may, I think, 

 be fairly concluded that if our coinage bars contain less than 0*5 

 per mille of bismuth their ductility will not be materially affected. It 

 must be borne in mind that these results only apply to bars of the size 

 and shape of those experimented on, and with the particular treatment 

 in lamination above detailed. With thinner bars and a different me- 

 thod of rolling, different results may be expected. The system of cut- 

 ting out blanks has also to be considered, for in some mints straps with 

 saw edges are not so prejudicial as in others. 



III. We have now to consider the best way of dealing with silver 

 tendered for coinage which is proved to contain bismuth ; and a few 

 remaining points. 



The only experiment on a large scale for refining such silver here, 

 as far as I know, has already been described. The want of success which 

 attended it seemed to be due to the very small amount of base metal in 

 the bullion, for the formation of a slag in which the bismuth oxide 

 could be entangled and removed by skimming ; and possibly the reducing 

 action of the plumbago pots used may have added to the difficulty. As 

 it seemed certain, however, that nitre would effect the desired oxidation 

 of the bismuth, some experiments were tried in this direction on a small 

 scale. About 20 troy ozs. of silver containing 2*5 per mille of bismuth, 

 and no other metal in appreciable quantity, was melted in a clay pot and 

 repeatedly treated with nitre and borax, the bath being skimmed from 

 time to time. After prolonged treatment in this way, the fineness of 

 the silver being three times tested by a dip assay, the report on the 

 silver was raised from 997'5 to 999*2 ; so there can be no doubt that 

 bismuth may be removed in this way. But the process, as several ex- 

 periments showed, is tedious ; and of course is attended with a loss of 

 silver which in large operations would be of notable amount. Consider- 

 ing therefore that silver containing bismuth has hitherto only been met 

 with at the Mint in bars of high fineness, and that these are not readily 

 refinable by the ordinary process, it would seem as well, if such silver be 

 accepted at all, to deal with the bismuth in it by the plan of dilution. 

 The proportion of bismuth any silver contains being ascertained, it may, 

 if convenient, be mixed by melting with sufficient silver free from bismuth. 



