BOOK XI.

IFFERENT methods of parting gold from silver,and, on the other hand, silver from gold, were dis-cussed in the last book; also the separation of copperfrom the latter, and further, of lead from gold aswell as from silver; and, lastly, the methods forrefining the two precious metals. Now I will speakof the methods by which silver must be separatedfrom copper, and likewise from iron . 1

The offlcina, or the building necessary for thepurposes and use of those who separate silver from copper, is constructedin this manner. First, four long walls are built, of which the first, whichis parallel with the bank of a stream, and the second, are both two hundred andsixty-four feet long. The second, however, stops at one hundred and fifty-onefeet, and after, as it were, a break for a length of twenty-four feet, it continuesagain until it is of a length equal to the first wall. The third wall is onehundred and twenty feet long, starting at a point opposite the sixty-seventhfoot of the other walls, and reaching to their one hundred and eighty-sixth foot.

x The whole of this Book is devoted to the subject of the separation of silver fromcopper by liquation, except pages 530-9 on copper refining, and page 544 on the separationof silver from iron. We believe a brief outline of the liquation process here will refresh the mindof the reader, and enable him to peruse the Book with more satisfaction. The fundamentalprinciple of the process is that if a copper-lead alloy, containing a large excess of lead, beheated in a reducing atmosphere, above the melting point of lead but below that of copper,the lead will liquate out and carry with it a large proportion of the silver. As the results areimperfect, the process cannot be carried through in one operation, and a large amount ofbye-products is created which must be worked up subsequently. The process, as heredescribed, falls into six stages. 1st, Melting the copper and lead in a blast furnace to form“ liquation cakes ”—that is, the “ leading.” If the copper contain too little silver to warrantliquation directly, then the copper is previously enriched by melting and drawing off froma settling pot the less argentiferous “ tops ” from the metal, liquation cakes being madefrom the enriched “ bottoms.” 2nd, Liquation of the argentiferous lead from the copper.This work was carried out in a special furnace, to which the admission of air was prevented asmuch as possible in order to prevent oxidation. 3rd, “ Drying ” the residual copper, whichretained some lead, in a furnace with a free admission of air. The temperature was raisedto a higher degree than in the liquation furnace, and the expelled lead was oxidized. 4th,Lupellation of the argentiferous lead. 5th, Refining of the residual copper from thedrying” furnace by oxidation of impurities and poling in a “refining furnace.” 6th,Re-alloy and re-liquation of the bye-products. These consist of: a, “ slags ” from

leading ” ; b, “ slags ” from “ drying ” ; c, “ slags ” from refining of the copper. All ofthese “ slags ” were mainly lead oxides, containing some cuprous oxides and silica fromthe furnace linings ; d, “ thorns ” from liquation ; e, “ thorns ” from “ drying ” ; /, “ thorns ”from skimmings during cupellation ; these were again largely lead oxides, but containedrather more copper and less silica than the “ slags ” ; g, “ ash-coloured copper,” beingscales from the “ dried ” copper, were cuprous oxides, containing considerable leadoxides ; h, concentrates from furnace accretions, crushed bricks, &c.

The discussion of detailed features of the process has been reserved to notes attachedto the actual text, to which the reader is referred. As to the general result of liquation,Aarsten (see below) estimates the losses in the liquation of the equivalent of 100 lbs. of argenti-erous copper to amount to 32-35 lbs. of lead and 5 to 6 lbs. of copper. Percy (see below)th ° te f resu * ts at Lautenthal in the Upper Harz for the years 1857-60, showing losses of 25% off 6 1 e:r ’ 9 - I % of the copper, and 36.37 lbs. of lead to the 100 lbs. of copper, or say, 16%o he lead; and a cost of £8 6s. per ton of copper. The theoretical considerations involved in1 9 1 ?^ aVe not keen satisfactorily determined. Those who may wish to pursue the subjectw nd repeated descriptions and much discussion in the following works, which have beenree y consulted in the notes which follow upon particular features of the process. It may been loned that Agricola’s treatment of the subject is more able than any down to the 18thcentury. Lrcker (Beschreibung Allerfurnemsten Mineralischen, etc., Prague, 1574).onneys (Benefit vom Bergwercken, etc., Zellerfeldt, 1617). Schliiter (Grundlicher Unterricht