EXPERIMENTS ON VARIOUS ALLOYS OF GOLD, 291- 



lt was not thought neceffary to extend the experiments, be- 

 caufe thefe metals have been much examined by other 

 chemifts *. 



GOLD ALLOYED WITH COPPER. 



From many experiments it appears, that the varieties °f ^^'ndsdr* 

 copper, in commerce, although fimilar in afpect, and other cop per render 

 obvious properties, are far from being uniform in quality; fo. gold brittle. x 

 that many of them are by no means fufficiently pure to be 

 employed as an alloy for gold ; but render it brittle. 



And the different effects produced by the moulds of iron 

 and thofe of fand, are fuch as fully prove, that copper which 

 is not perfectly pure, and which has a tendency to render gold 

 brittle, ads more powerfully, in this refpect, when the al- 

 loyed mafs is caft in fand than when it is caft in iron ; and, all 

 things being conlidered, there is reafon to conclude, that 

 moulds of iron are much to be preferred to thofe of fand f. 



The ores of antimony and of lead frequently accompany "" m0 ^ P r0 " 

 thofe of copper ; and it has already been proved, that T ^- of timo^y^lcad, 

 either of the former metals is fufficient to deftroy the ductility 

 of gold. It may therefore be fufpected, that the brittle quality 

 which certain kinds of copper communicate to gold, proceeds 

 from thofe metals ; for, though other metallic fubftances produce 

 the fame effect, yet, as the former efpecially are fo commonly 

 prefent with the ores of copper, it is highly probable that 

 antimony, or lead, may remain combined with the fmelted 

 copper, in a proportion too fmall to afiect the general and 

 more obvious properties of that metal, yet ftili fufficient to 

 deflroy the ductility of gold, when fuch copper is employed 

 as an alloy. 



To afcertain how far copper might be alloyed with lead, or Copper may con- 

 antimony, without any very apparent change in its obvious p^ion of lead 

 properties, the following experiments were made : or antimony, 



and be very 

 * Gold made ftandard by platina, is not only very ductile, but merchantable, 

 alfo (when hammered) tolerably elaftic. perhaps it might be ad- 

 vantageoufly employed for the fprings of watches, Sec. C. H. 



f Bars of alloyed gold (particularly thofe which are alloyed 

 with copper) are generally difcoloured on the furface, when caft in 

 moulds of fand ; but not fo when caft in iron. It may be fufpected, 

 that the alloy is fuperficially oxidized when fand is employed, in 

 confequence of the air which is lodged in the interftices, together, 

 perhaps, with feme degree of moifture. C. H« 



U 2 To 



