MR. Thomson's purification of gold and siLvi^it'; 1^3 



XVIII. 



A netv and cheap Method of purifying Gold and Silver, By 

 Andrew Thomson, Ejlj. of Banchory, near Aberdeen, 

 In a Letter from the Difcoverer. 



I 



To xMr. NICHOLSON. 

 SIR, 



INTENDED to have deferred the prefent communication ^hls pubUcatlo^i 



till fuch time as I Ihould have it in my power to lay before the^^^^^^ becaufc 

 public the complete (eries ot" experiments in which I have the inventor 

 been engaged with regard to the purification of gold ^"^ ^ficLatg^d/ ■ 

 iilver. But unluckily I mentioned a few particular circum- 

 (lances with regard to them, to a man who took it upon him, 

 without my knowledge, to fend an account of them for 

 publication to a periodical work. As I underhand that work 

 will not appear fo foon as your next number, I beg, if you 

 think it worthy of a place, that you will infert the following 

 account of fome attempts I liave been making to purify the 

 precious metals. 



Being much at a lofs for want of a crucible of pure filver P''°"fs "f 

 far the analyfis of fome minerals, and as all the ufual methods tracing copper' 

 pra6liced for purifying that metal are very troubleforae, I fet from bell-metaU 

 niyfelf to confider the various operations on metals, in hopes 

 of falling on a more fimple way of accomplifhing my purpofe. 

 At length, I found a procofsof Pelletier's, which promifed to 

 fucceed, and mine is merely extending his idea a little further 

 than he did himfelf. 



He was, I believe, employed by the French governments^ oxides die tin 

 to difcover an eafy way of feparating the tin from copper on. ^^^^^^^ ^> 

 belUmetal, and the procefs he gave, is this. Upon the 

 melted bell-metal projed black oxide of manganefe in powder, 

 frequently ftirring the metal till all the tin becomes OJiidated 

 by the manganefe. He adds a caution, not to add too rtiuch \^ fuchpropor- 

 manganefe, otherwife part of the copper aUb will be affeft^he^ '** 

 deftroyed. copper. 



It immediately ftruck me, that in this way I might be able The author's 



to oxidate the copper which alloys cur filver, and ^V^^'c^^t^^crf^i 



making the trial I fucceeded completely ; I had fome impure rolled outj then 



filver rolled out to about the thicknefs of a niilling, this I^°^!^'^"P» 



*^ bedded m man- 



coiled ganefej and 



