tke Sulphureous one of Copper by Lead. . j<.^ 



A Heflian crucible muft be perforated at the bottom, and both its internal and external 

 furfaces coated with charcoal-dufl and loam. This crucible is then placed in another 

 calice-formed crucible (kelchtutte), or into a black-lead crucible, properly cut for that 

 purpofe, and likewife internally coated with powdeired charcoal. In this it is faftened by 

 means of a wedge made of clay, in fuch a manner that it cannot elevate itfelf during the 

 experiment. A determinate quantity of lead, altogether free from filver, is then fufed in 

 the interior crucible, through the aperture of which in the bottom it flows into the exterior 

 veflel. The quantity of lead fliould be fufficient to occupy part of the inner crucible: 

 And to prote£t it againfl. oxydation, its furface muft be covered with fome powdered 

 charcoal in both veflels. Upon this fome powdered copper-mat, that has undergone the 

 fecond or third roafting, is introduced into the inner crucible, and melted by a fire fufH- 

 ciently ftrong and briflc, fo that it may flow thin. The putting in of frelh copper-mat is to 

 be continued, til! the interior crucible can hold no more, when in thin fuGon. The fluid 

 copper-mat prefles the fufed lead in the inner crucible, through its aperture at bottom into ' 

 the outer, and at laft itfelf follows, and rifes up through the lead, and giving out its 

 portion of filver during its tranfition. That portion only of copper-mat which remains in 

 the inner veflel will continue to preferve its filver,- The • aipparatus is then fuffered 

 to become cold without agitation, and after breaking the veflels, the whole of the lead and 

 copper-mat refting upon it in the outer crucible are to be colledled, feparating them 

 carefully from each other, and cleaning them from the adhering charcoal-duft. Their 

 weights are next to be exadlly determined ; after which the lead is aflayed for filver, and 

 the copper-mat, deprived of its filver, is aflayed.for copper. A calculation may be made 

 from the refults of the quantity of filver obtainable from a certain determinate quan- 

 tity of copper. 



If the copper-mat has not been duly roafled, and, confequently, ftlll contains too much 

 fulphur, it will difl"olve a portion of filver in this procefs, and a lofs will be obferved in the 

 remaining lead, which will be greater in proportion as the fulphur in the copper-mat is 

 lefs faturated with copper. But if the copper-mat, by too much roafl;ing, has been 

 brought below the point of faturation of the fulphur with the copper, part of the copper 

 will then feparate during the fufion, and, mixing with the lead, will occafion an increafe 

 of weight. 



On making experiments with the copper-mat from Rothenburg, I found chat a mixture 

 of that which had fuftained the third roafting heat, with an equal portion of that which 

 had been fubjefted to the fecond roafting, was the beft fuited, and of fuch a quality, that 

 the effett was quite fatisfaftory. 



Out of many different experiments, which I have made in order to put my method to 

 trial,, and which afforded very uniform refults, I (hall in this place give an account only 

 of the laft I have made. 



Co'p^cr-m?ii ixom Rothenburg, mixed in equal parts of that of the fecond with that of 

 the third roafting, waj made to pafs, in the manner above explained,, through 24, centners 



of 



