METALLURGY. 



65 



**> sulphur, and with the *coria of a former process. The 

 mixture is fuaed in a blast furnace, anil the sulphur 

 unites with the silver, with the lead, and with the cop. 

 per. The matter, during cooling, separates into two 

 part* ; that below, amounting to about one-fourth, i* the 

 silver mixed with lead, copper, iron, sulphur, and arse- 

 nic, and is roasted to expel the two jast ingredients, 

 and to oxidate the iron. It i* then mixed with about 

 one and a half of rich ore, and some scoria, and is fused. 

 The metallic matter thu* obtained ia again roasted, 

 and fused with about one-half of litharge, and a* much 

 scoria. When cold it separate* into three part*, 1st, 

 lead mixed with silver; 9d, copper and silver; 3d, 

 scoria, abo containing copper. The second of these 

 ia mehed with lead and copper scoria, and afterward* 

 with litharge and scori, by which the silver unite* 

 with the lead. Should the whole of the copper not be 

 removed, the metal must be repeatedly fused j by 

 which not only the copper, but the other impariti** 

 panted. The scoria of this proceaa i* kept and 

 with ore in other operations. 



i ** t:, 



copper by the proc*** of eliquat ion. 

 1 ver ore i* performed by melting the alloy of copper 

 and river mixed with lead, or with litharge and char. 

 coaL For this purpose a Mart furnace is employed, 

 having it* bottom lined with charcoal, beat together, 

 and forming an inclined plane. Whan the furnace M 

 filled with charcoal, to which some MO- 

 , which, by the heat, i* faaed, and adhere* 

 i of ln*t fix rnact . A ouMiti ty ov MSBO md 

 M then thrown in, and afterward* litharge 

 mixed with charcoal. Another quantity of the allay 

 and litharge fa than added, and lastly some lead. By 

 the application of a strong heat, these substance* an 

 fused, and the litharge ia reduced by the charcoal ; the 

 "I matter collect* at the bottom, and is drawn off 



quantity of copper, otherwise the whole of the silver Meullur- 

 will not be extracted. On the contrary, it should not gy- 

 exceed four times the quantity of copper, otherwise V "^"Y""**' 

 part of that metal will be carried along with it and the 

 silver ; the proper proportions therefore are between 

 three and four parts ; the exact quantity will of course 

 depend on that of the silver. It is necessary also, that 

 the ore contain a certain quantity of silver, otherwise 

 the process is not complete. From one to three- fourths 

 per cent, seem the best. Should therefore the different 

 ore* have different quantities of this metal, they must 

 be mixed so as to get a collection, which contains the 

 proper proportion of it. 



In Germany, where the copper alloy contains about 

 three-fourths per cent of silver, the proportions of the 

 substances employee), are three of the alloy, and eleven 

 of lead. When the alloy does not contain so much 

 silver, about ten of lead are used. If instead of lead, 

 Ktbarge be employed, 120 of the latter must be used 

 for each 100 of the former, that were requisite. 



Alto*. The word assay, in its extended sense, means Astir, 

 the analysis of the different metallic ore*, with the view 

 of ascertaining the quantity of valuable material* which 

 they contain ; in it* more limited acceptation how. 

 and in which sense it is usually employed, it signifies 

 the proc*** followed for ascertaining the quantity of 



ktatVL 



roi* added 



t,, t',.- : ! - 



of tbealloy 



1- _ 1 '.L - __ ___ ____ '- .. -I., 



mMQ wnn day, ana previously 

 While the octal in thaw i* in a state of fusion, a bar 

 of iron bent at the end is plunged a little way into it, 



* L!_L .. I* M*v,.Krl ^wfL^Mk nl*l AwHM tlhA wk 



Dy wnicn it is removcQf wnen 0010, iron toe *a 

 The loave* are then placed in a furnace, on 



and silver, either in an ore, or in alloys of these 

 metal*. In a Mill more limited sense, it applies only 

 to the analyiis of the latter, as in determining the 

 quantity of gold or silver in plate, coins, and articles of 

 jewellery. The assay of gold and silver alloy* requires 

 to be unfa and with very great care, a* it i* done on 

 a very small scale. Before a piece of plate can be 

 turned, it must be assayed. For this purpose, before 

 it ia fcnahad, it ia taken to the assay-master, a person 

 in the pay of the Company of Goldsmiths, who scrapes 

 off a small quantity of it at different places : these he 

 together, and set* aside for the assay. The 



is practised with the other alloy* submitted to his 



ban of 



each other b 



brick*. By the 

 , and run* along 



application of neat, the lead is meTted', and run* along 

 a groove in the lower part of the furnace, carrying 

 with it the silver. In thi part of the procaa*, great 

 can moat be taken not to raise the heat too high, 

 otherwise part of the copper win be mehed and ran 

 out with the lead. Whan the lead cease* to flaw from 

 the loave*, the fin must be Mopped, after which the 

 -,-ft in the state of a reddish *pongy mat*, 

 ammg a minute quantity of silver, pernap* not 

 an ounce in the 100 pounds ; they are 

 therefore" expoeed to heat, by which a metallic matter 

 exude* from them, consisting of silver, lead, litharge, 

 arsenic, and scoria, and if the heat ha* not been cau- 

 tiously applied, of some copper. When the metal 

 which exude* ha* a reddish colour, the process must 

 be (topped. The metal procured by this operation i* 

 freed or tome of its impurities by washing, and is then 

 objected to cupellation. The copper left in the fur. 

 nace i* nearly pure. 



In the first part of this proces*, the beat mutt be lam 

 than what is ncceaaary to melt the copper; and by 

 aamg. litharge and charcoal instead of lead, the opera- 

 tion u expedited, because the litharge, before it is re- 

 duced, proves a good flux. If lead be employed, it 

 abomld am Mill, at laatt, to two and a half time* the 



VOL. xiv. MBT i. 



treating of gold, it was mentioned that it and 

 ilver reaist the action of heat and air, while the other 

 metals with which they are alloyed, are oxidated at a 

 high temperature. On this depends the aasay of gold 

 and *ilver alloy*. For the complete tuccets of this pro. 

 earn, it i* ntemary that the quantity of base metal be 

 Ian*, otherwise the attraction between the noble metal 

 and h prevent* their separation. For this reason, a 

 quantity of lead i* always mixed with the alloy. The 

 aparatlon of gold and silver from other metals, by 

 of lead, i* called cuptUaitan, and the process i* 

 pel funned on a c*pci placed in a muffle. A cupel i* 

 a diah of a circular or pyramidal shape, made of bone 

 aahea, and having a small depression on it* upper sur- 

 face, into which the alloy i* put. A muffle i* a vessel 

 madr of earthen ware, flat below, and arched above, 

 open at one end, and shut at the other, and at the sides, 

 except where it i* perforated by small hole*. The fur- 

 nace employed in cupellation, i* one in which a strong 

 heat can be excited, and having a hole in it* sides for 

 the admission of the muffle. W'hen the cupellation is 

 to be performed, the muffle is placed in the furnace, to 

 which it i* generally secured by luting. The furnace 

 i* then kindled, and the muffle and cupel* are slowly 

 heated. When these are red hot, the alloy, beat out to 

 a thin plate, and rolled up in a sheet of lead, obtained 

 by the reduction of litharge, i* put into the cupel. To 

 prevent the air which enters the muffle from lowering 



