The silversmith's handbook : containing full instructions for the alloying and working of silver, including the different modes of refining and melting the metal; its solders; the preparation of imitation . bonate of potash may beadvantageously dissolved in the water; the latteris then applied in small quantities at a time to thebone-ash until the proper coherency has beenobtained; of the total quantity of bone-ash em-ployed in the operation, 2 per cent, of potash willbe quantum sufficit to mix with it. The iron frame,or test, is then filled with the mixture, and it ispressed down in
The silversmith's handbook : containing full instructions for the alloying and working of silver, including the different modes of refining and melting the metal; its solders; the preparation of imitation . bonate of potash may beadvantageously dissolved in the water; the latteris then applied in small quantities at a time to thebone-ash until the proper coherency has beenobtained; of the total quantity of bone-ash em-ployed in the operation, 2 per cent, of potash willbe quantum sufficit to mix with it. The iron frame,or test, is then filled with the mixture, and it ispressed down into a solid compact mass, the centrepart being hollowed out with a small trowel, thesides sloping towards the concavity in the middle;the hollow should not however be extended more than within i to i^ in. ofthe bottom of the frame,and above the iron cupel forms thehearth of the furnace wehave spoken of, and ofwhich Fig. 13 is a sec-tional view; it is remov-able, and not a fixture inthe furnace. It must be left for several days to tmsimi^MSMmi^M^^Mi^mm dry, after havmg been Fig. 13. Cupels, section and perspective , .11 views. constructed as described, when it is ready for use, and only requires firmly. THE CUPEL. 33 wedging in its place beneath the arch of thefurnace. The fire should be only very moderate atthe commencement of the operation, and thefurnace slowly raised in temperature, lest thecupel should crack by being too quickly the temperature increases, if without anyapparent defects in the bone-ash cupel, orhearth, which it may now be termed, the wind orblast, generally driven by a fan, is thrown inthrough a nozzle, or an aperture in the furnace,which, for facilitating the immediate removal of thebone-ash hearth, is placed upon an iron car, andruns beneath the vault of the furnace on rails, sothat it may thus be very readily withdrawn whenfound necessary. The admission of a current of airinto the furnace oxidizes the excess of lead, in com-bination with
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectsilverw, bookyear1921
