METALLURGY. 



67 



ver. Other* recommend a smaller quantity of lead. 

 Tbe proportion of lead added to gold alloys i* nearly 

 the same. 



After the cupellation, the product must be subject- 

 ed to the process of parting, which is nearly the same 

 as has been described when explaining the method* 

 practised in tbe purification of gold. For this purpose, 

 the coil of metal is put into a pear-shaped glass vessel, 

 with two or three times it* weight of slightly diluted 

 nitric acid, and beet ia applied, by which tbe acid act* 

 on the silver, and leave* tbe gold. When the action 

 " , which i* known by tbe cessation of the red 

 the coil ia left corroded, but unbroken ; the 

 i then poured off, another quantity of acid is 

 boiled on it for a few minutes, and again decanted off; 

 the vessel ia then filled with water, and inverted, by 

 which the coil fall* out entire. The mrtal is afterward* 

 subjects*! to a high temperature, by which it shrinks, and 

 at last forms a button of resplendent gold ; after whiih 



accurately weighed. Tbe silver in aolut, 

 obtained by the immersion of a piece of copper, or by 

 the addition of common salt, and fusion with pearl 



his of greet eon 



1 _ 



i these ere in I 

 in B|hM Mfe 



to be able, by eey methods, 

 with which it is alloyed, 

 portion, ae in gold lace, and 



In teparating gold from gold lace, the metal ia fused 

 and granulated, by pouring it into cold water. It ia 

 then treated nearly in the same way as has been ex- 

 plained for separating gold and silver, when the Conner 

 M in small proportion. 



For this purpose. quantity of the granulated natal 

 is mixed with one eighth of flowers of sulphur, and 

 kept in s state of fusion lor about am hour, or till a kind 



kept in a state of reason far about 



QB lUMUftC pptaTdTB QB Itf 8 



granulated metal, canal to 



quantity of the 

 ' part of 



the weight of that fused with the sulphur i* mixed with 

 one-half its weight of litharge, and one-eighth of tan. 



port,,-,-.. kHm*Mimixt , !...' well r . ,.| 

 each addition. After this ia added, tbe mixture is kept 

 in the fused state for about ten minute*, and the upper 

 part of it, which i* silver in union with sulp!. 



tbe iimailiilir is then poured into greased 



^ a state of fusion, 

 of alloy, litharge 



e way aa i " 



r | >r< '< ! U' * i - t '.r - 1 . : '. i i > i r. 



At the bottom of the cones a metallic mattir, 

 poaed of silver, with almost tbe whole of the gold, is col. 

 lected. The enbstance above this, still, however, retains 

 a little g. t-erefore again fused, and a small 



quantity of an alloy of equal part* of copper and Iced 

 ia mixed with it, by which tbe whole of the gold is se- 

 parated, or collected at the bottom of the cone into 

 which the mixture i* poured. 



The different portion* of metal procured are mixed 

 and fused with one-eighth of lead, and treated in tbe 

 seme way a* before, with sulphur, the mixture of alloy , 

 latharg*. and sendi ver. \V bat is collected is then fused 

 with one sixteenth part of >ulphur, and kept in that 

 state for half an hour. It is then poured into the cone, 

 the silv er and tatptmr collect at tbe top, and the gold 

 talk to the bottom. Tbe sulphuret of silver mutt again 

 and aain be fused with sulphur, till the whole of the 

 Tbe gold collected i* then fused 



and again be fusee 

 gold M separated. 



with one-sixteenth of copper and granulated; the same Metallur- 

 quantity of sulphur is now mixed with it, and the mix- P?- 

 ture is fused for about a quarter of an hour, and then ""^~" 

 poured into a cone. The gold found at the bottom of 

 this, is afterwards purified by sulphur and antimony, 

 a* already described. 



In gilded copper good* the quantity of gold is very 

 trifling, still, however, it is of consequence to separate 

 it from the other metals ; this is done in two ways : 1st, 

 The gilded metal is fused, and granulated, after which 

 it is again fused and flower* of sulphur are gradually 

 added, till the whole becomes dark- coloured. When 

 cold, it is reduced to powder, and amalgamated, as al- 

 ready described when treating of the ores of gold. By 

 this means tbe mercury combines with the gold, and 

 leave* sulphuret of copper. 



Id. The metal is brought to a rtate of fusion, and 

 about an equal quantity of a mixture of litharge and 

 sulphur, previously fused together, is added to it, and 

 the whole is well stirred. Charcoal in fine powc. 

 then thrown in, in small portions at a time, the mixture 

 being constantly stirred with a copper rod. ]!y this 

 meani the litharge i* deprived of its oxygen, and the 

 lead falls to the bottom, carrying the gold along with it. 



Tbe alloy of these metal* is then subjected to the 

 process of cupellalion, by which the gold is obtained 

 pure. 



The quai <<! copper goods is often 



so great, as to make it an olject < . .able im- 



portance to be able to separate this metal from the 



The process for separating silver and copper, wlun 

 the former is in large quantity, has been already ex- 

 plained, but the proportion of the latter metal in ) 

 good* u so great, that the silver cannot l>y these i. 

 be obtained from them, because they will not bear to 

 be alloyed with a sufficient quantity of lead ; recourse 

 must therefore be had to other method*. 



Tbe beet mode of separating copper and silver in 

 plated goods was recommended l>y Mr. Krir. This 

 gentleman <li-< ovrred, that an acid composed ol 

 phuric and nitric acids did not act on copper, while it 

 dissolved silver ; be therefore applied this to the se- 

 paration of these metal*. For this purpose, 1 Ib. of ni- 

 tre is dissolved in 8 Ib. or 10 Ib. of sulphuric acid, with 

 the aid of a gentle beat, in a gUzed earthenware 

 Piece* of tbe good* are then thrown in, and the heat 

 is raised to about the SOOdth degree. \Vhen the whole 

 of the silver is dissolved, the fluid is poured off, and the 

 metal is precipitated by muriate of soda, and is ob- 

 tained in the usual way ; or the solution is diluted v ith 

 water, and pieces of copper are immersed in it, by v 

 the silver is precipitated in the metallic form, the dilut- 

 ed acid acting on tbe copper. 



There U still another method of separating silver 

 from copper, by means of the black oxide of manganese, 

 when the silver is in large proper! 



The process consists in thin pieces of tbe 



alloy, surrounded by black oxide of manganese, to an 

 intense heat, by which the metal is melted, and a black 

 powder is procured. This is mixed with three times 

 its bulk of pounded green glass, and again exposed to 

 a strong beat, after v silver is obtained pure at 



the bottom of the vessel. In die first part of this pro- 

 cess tl and copper are oxidated, and in the 

 latter, the oxide of silver is reduced by heat alone, 

 whereas the oxide of copper requires tbe presence of in* 

 flammable matter for its reduction. 



