56 J. F. Tennant—Euxperiments [No. 1, 
VI.—On some experiments made at H. M.’s Mint in Calcutta on coining 
Silver into Rupees.—By Cou. J. F. Tennant, &. E, F. RB. 8., &e., 
Master of the Mint. 
(Received 22nd March ;—Read 2nd April, 1879.) 
It has long been known that when an alligation containing fine silver 
and copper has been melted the result is an apparent refining, and the 
result of the further processes in coining is also to change the constitution 
of the alloy. In order, therefore, to produce Rupees of standard weight and 
fineness, it has always been found necessary to allow for these changes. The 
rule by which this allowance was made, however, did not seem to me to 
have any good foundation, and, while generally speaking the results were 
fair, there were occasional departures which convinced me that it could be 
improved, The rule here has been to make the alligation to standard 
43 of silver: scissel being assumed to have this fineness—then copper was 
added in proportion to all the silver except scissel, so as to reduce the fine- 
ness and this “ extra alloy” was subject to variation on different coins. 
It was clear then that silver in the form of scissel was not supposed 
to refine, and next that the whole of the change was not supposed to occur 
in melting, but partly to depend on the further processes. The last was a 
matter which was evidently more than probable; and as regards the first 
Col. J. T. Smith, late Master of this Mint, had many years ago shown that 
after a time a silver alloy ceased to refine. It seemed to me more than 
probable that this last result was only an approximation to the truth, and 
that the fact was that copper when mixed (at all events in small quanti- 
ties) with silver was not exposed to oxidation in the furnace ; but on this 
hypothesis it became absurd to add extra alloy on silver of 900 milliémes 
of fineness as on fine bars. I thought too that I saw that the variations 
which such an error would cause really took place, and resolved therefore 
to investigate the whole matter experimentally. 
Silver at this Mint is reported to 0:2 of a milliéme: when an alliga- 
tion is made, it is usually arranged that there shall not be a great number 
of finenesses used, and as each quality will be composed of several samples, 
these are all mixed in a heap, so that the silver used is the average (rough- 
ly) of several samples all reported alike. This procedure generally allows 
all the pots of a day’s melting to be practically identical in fineness and 
weight, and if this be not the case it is very rarely that there are not 
several similar pots. ‘There were no cases of single pots in-this work, 
though owing to a small stock of silver, the whole in each melting could 
not be made alike. 
