72 



,Gold not com- 

 pletely purified 

 by the ufual pro- 

 cefles of parting. 



Antient pro- 

 files. ■ 



Quartation. 



Fufion witb, 

 nitre. 



Granulation. 



Parting by nitric 

 acid. 



DESCRIPTION OF A NEW PROCESS OF REFINING. 



This is feen by a (ingle experiment; but practice foon Chows 

 that for this folution to take place, it muft be made upon an 

 alloy of one part gold with four parts filver, and that it will 

 be more perfecl the greater quantity of concentrated acid is 

 employed, or the higher the degree of heat which is applied 

 to the velTels. Thefe obfervations improve the art, but do not 

 bring it to that point which will enable us to obtain the gold 

 in its greateft purity, for this metal very rarely comes from the 

 crucible more pure than 998 or 999 in a thoufand. 



In this ftate it was that I found the art at my entrance into 

 the national refinery, where being placed as it were in com- 

 petition with the refiners of commerce, I fought the means of 

 improving the procefles already known, and I now offer to 

 the arts, that which has conftantly fucceeded with me during 

 two years operations carried on in the laboratory of Cit. Dize. 



I (hall begin with defcribing the old procefles of refining, 

 and afterwards explain the method which I have fubftituted in 

 their (lead. 



The ingots received in commerce by the refiners are more 

 or lefs rich, and more or lefs mixed with the fine metals, but 

 their purity is generally between 850 and 950 thoufandth parts. 

 They mix thefe ingots and unite them by fufion, fo that the 

 alloy intended to be formed fhall contain four parts of filyer to 

 one of gold ; they pour thefe alloys out in grains, and add to 

 every five kilogrammes 500 grammes, to the amount of 650 

 grammes of nitrate of potafh of the fecond boiling *, 



The mixture is then melted in crucibles, where it is fuffered 

 to cool in a mafs, and thefe mafles are again fufed and granu r 

 lated, to multiply the furfaces of the alloy to be fubmitted to 

 the action of the nitric acid which is employed ip the parting. 



To perform this operation, the refiner diftributes the grains 

 in pots of ftone-ware, and pours two parts of nitric acid of 

 30 degrees over one part of the alloy. He places thefe pots 

 in a fand-bath, in order to affift the aclion of nitric acid upon 

 the filver, by means of the heat. When the folution is ef- 



* The intention of this operation is to oxidate the copper and the 

 other metals which are mixed with the gold and filver j and in fa£t, 

 by this fufion, which is called (poujfee) the purity of the mafs is 

 J?rought to about .378 : hence the quantity of acid neceflary for its 

 folution is much diminiftied. 



fected, 



