31 V1.-On ReJiniiig Gold when alloyed with Tin or Antimony so us to render it $t for the purposes of Coinage. BY ROBERTWARINGTON. TOWARDS the latter end of the year 1857 I received from the Australian Bank a specimen of bar-gold for analysis mhieh was stated to have been obtained from the quartz-crushing process. On the exterior or what had been the surfaces of the original bar it presented the general appearance of a golden hue though perhaps an experienced and critical eye might have considered it a little paler than pure gold. Interiorly or on the broken surface however it had a crystalline structure of a greyish yellow colour. It was very brittle and rotten and by analysis yielded the following results on the 100 parts. Gold . . 92.50 Silver .. 4%0 Tin . 2.00mitli a trace of antimony Copper . . 0'75 99.75 Loss . 0.25 __.- 100*00 I have been informed that numerous bars of this white and brittle gold had arrived in this country from Australia and had caused much trouble and annoyance to the refiners rnelters and also to the Mint officers as it will be evident that the nature of the alloying metals is not rendered apparent in the ordinary mode of assay by the processes of cupellation and quartation they being oxidized dissolved and carried into the crtpel with the lead; and that therefore in the after larger operations of melting when the gold passes forward for the purposcs of coinage the existence of the tin and antimony not having been discoverd is iiot provided for and consequently from the brittle nature of the alloy the subse- quent processes of rolling to which it has to be subjected are rendered impracticable I am informed that about 47,000 ounces of gold bars have in this condition been returned to the Bank of England authorities from the Mint as unfitted for the purposes of coinage.WARINGTON ON REFINING GOLD WHEN A short time after the foregoing examination was completed and reported on I received another specimen of this brittle gold for analysis through other parties. This seeorid sample presented somewhat the same appearances both externally and internally as the one just described being perhaps a little whiter in its colour and more rotten or friable in texture. It yielded by analysis on the 100 parts :- Gold .. 93.88 Silver . 2.20 Antimony . . 2.28 Tin . . 1.40 Copper . traces 99.68 Loss . . 0.32 -100 An interesting question arises from the above results as to the origin of these injurious alloying metals ; do they occur associated with the gold or are they introduced during the melting process ? As regards the first we know that in stream works gold and oxide of tin are commonly found associated as is the case in Ceylon in Cornwall and other districts. We know also that considerable quantities of stream-tin are brought from Australia. The presence therefore of that metal in small quantities as an alloy in the re-sulting gold bars might be almost anticipated. But this view of the case does not account satisfactorily for the other alloying metals found in the second analysis particularly the antimony.My own impression derived from a careful examination of the specimens and the foregoing results is that they are introduced during a rough process of refining through the employment of sulphuret of antimony and that for want of efficient management the operation has been imperfectly carried out;. The use of sulphuret of antimony for the purpose of refining gold and raising its standard is so well known that I need hardly dilate upon it; suffice it to say that if successfully applied it converts the iron zinc tin &c. that may be present and much of the silver into the form of sulphurets which float in their melted state upon the surface of the gold; a portion of the antimony at the same time alloying with that metal.This antimony should of course be afterwards removed by a second ALLOYED WITH TIN On ANTIMONY. operation.* From a specimen which has since come into my possession it will be seen that the particles of gold dust have been so imperfectly melted before running into bars that many of them are still visible in their flattened and rounded forms and must therefore have remained suspended in the melted alloy. I feel that this explanation of the source of the alloying metals is therefore to some extent substantiated as a want of a sufficiently high and continued heat would leave the gold very much in the state above described. On delivering the report of this second analysis to the parties from whom I had received the sample they were anxious to know if I could suggest to them a method by which these injurious alloys could be removed and the gold rendered capable of being rolled or hammered without at the same time greatly increasing the expense of the operations or entailing a loss of the gold.I was in consequence induced to turn my attention to the effecting of this desirable object. The proper resolution of this problem required a little consideration inasmuch as although it was evident that it must be accomplished by a process of oxida- tion to burn out ps it were the antimony and tin; yet it was also necessary that the oxygen should be applied to the alloyed gold while the metal was in its fluid state and also that the oxidiz- ing agent should not part with its oxygen simply by the high temperature to which it would be subjected.Nitrate of potash I was informed had been suggested tried and failed although a very large percentage had been used; experi- ments in that direction were therefore considered unavailable and my attention was consequently turned to the employment of metallic oxides having a weaker affinity for oxygen at these high temperatures than the metals which it was required to remove from the contaminated gold. After a few experiments all of which were more or less mccess- ful I succeeded in obtaining the desired result and submitted for the consideration of the parties concerned a simple proccss which from their liberality I mas enabled at the time to corn-municate to several friends interested in such matters and which I also desire now to lay before the members of the Chemical Society.The process consists in the employment of oxide of copper about 10 per cent. of which is to be added * Since making this communication I have been informed that sulphate of antimony also sometimes occurs in association with native gold in Australia. VOL. XIII. I) WAWNGTOPr’ ON REFIXING GOLD. to the alloyed gold with the addition of a small quantity of borax and the whole maintained in a well fused state for about half an hour. The result is a pd’ectly malleable gold containing a small percentsgc of metallic copper and wcll fitted for the purposes of coinage. The proportion of oxide of copycr used must of course greatly depend on the percentage quantity of the oxidable metal requiring to be removed; but I believe from the specimens which I have worked on that it never need exceed the 10per cent.Oxide of manganese might be employed to effect the same purpose; but I found that the fuvibility of the oxide of copper and its powerful fluxing properties rendered its actioti much more efficient and complete from its flowing continually over the surface of the molten gold and thus thoroughly oxidizing and removing the tin and antimony from their combination. As thus conducted the resulting alloy should a!mays be better than standard unless the baser metals occur in very large proportion. By the action of nitro-hydrochloric acid upon these samples of alloyed gold the resulting solution deposited on cooling beautiful crystals of chloride of silver; and I may be allowed here to mention a very curious case of the same kind but to a much greater extent which was brought under my notice some time since by the late Mr.Maurice Scanlan.It appcared from his statement that he Bad been requested to obtain the gold from a beautifully wrought and small sized rope-chain of Indian manufacture ;and on submit- ting it to the action of nitro-hydrochloric acid for this purpose hc found that it did not dissolve ; and although he obtained some gold in solution yet the form and size of the delicate fabric remained unaltered ;it had become however very brittle and rotten and mas of a dingy brown colour.It was submitted to me for examination by the microscope and when subjected to this scrutinizing agent it was at once evident what had taken place and of what the chain had been compoued. It consisted almost entirely of chloride of silver beautifully crystallised on the surface or strands of the rope .and having in the cross section a radiating structure from the interior to the circumference the central core in some fragments exhibiting still a portion of the original alloy from which the gold had not been removed it having most probably been protected from the action of the acid by the comparatively thick coating of chloride of silver which had bsen formed arouiid it.