EXPERIMENTS ON VARIOUS ALLOYS OF GOLD. 293 



require copper to be as pure as poffible. Perfons of this de- 

 fcription, however, are liable to be deceived; for, in 1791, 

 Mr. Roitier, Director of the Mint at Paris, purchafeda quan- 

 tity of copper from the mines of Poullaoen in Britany ; but he 

 foon difcovered, from the effects which it produced, when em- 

 ployed as an alloy, that it was not pure, and therefore request- 

 ed Mr. Sage to examine it. By the latter, it was anatyfed, 

 and was found to contain one forty-eighth of antimony *. 



Allowing, therefore, that other metallic fubftances may at Antimony is 

 times be prefent in copper, and may contribute to affect gold JjJ° noxwus ad» 

 which is alloyed with it, yet, for the reafons above related, dition. 

 the author is inclined to attribute, mod frequently, this effect 

 to antimony or lead. 



Copper which is pure, is uniform in its effect, and does not 

 injure the duclility of gold ; it would therefore be proper in all 

 cafes when copper is to be purchafed for the purpofe of alloy- 

 ing gold, to make a previous trial of it on a fmall quantity, as 

 this would anfwer every purpofe of a tedious and expenfive 

 analyfis. 



Since the above was written, he made various experi- Farther exam!, 

 ments in the humid way, on the d ifferent kinds of copper, JJ^SljH?* 

 which are known in commerce, efpecially on the following: 



No. 1. Fineft granulated Swedifti copper fp. grav. 8,895. 



2. Swedith dollar copper - fp. grav. 8,799. 



3. fheet Britifti copper - - fp. grav. 8,785. 



4. Fine granulated Britifti copper - fp. grav. 8,607. 

 480 grains of the firft, only afforded a few particles of ful- 



phate of lead, which could not be eftimated. 



The fecond contained both lead and antimony, of which the 

 lead was in the largeft proportion, as it amounted to nearly one 

 grain of metallic lead, whilft the antimony did not exceed half 

 a grain. 



The meet Britifti copper yielded fome lead, with fcarcely 

 any antimony; and, on the contrary, the granulated Britith 

 copper contained antimony with but very little lead. We may 

 therefore conclude, that the varieties of copper known in com- 

 merce, are feldom, if ever, abfolutely free from lead or anti- 

 mony ; and that the brittle quality, fo frequently communicated 

 to gold by an alloy of copper, arifes from the pretence of one 



* Journal di Pbjfiqu*> H92, Tome XL. p. 273. 



or 



