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heated, till the metal flows. At this high temperature the lead is oxidized and gradually absorbed as oxide by the porous material of the ash floor. The red oxide of lead or litharge forms at the end one solid mass with the bottom and is called then Mitsuda-do or Gin-rokasu, Syn. Shiro-kané-ro-nerisoko. This mixture of ash and litharge is afterwards worked for lead, for which purpose it only wants to be smelted with some charcoal, to reduce the oxide of lead. During this operation the silver is not oxidized and is therefore not absorbed by the porous ash-bottom. At last the silver, mixed with a little oxide of lead and lead metal, remains in the cavity of the cupel bottom. The furnace is then allowed to cool. The remaining metal is finally cooled with water and taken away. It bears the name of hai-buki-gin (silver smelted upon ash).
4th.—Refining the silver.
The cake of impure silver is placed in another small cupellation furnace with a fresh ash-bottom. The heat must be regulated carefully, otherwise the silver would be partly thrown away by the sudden discharge of absorbed oxygen. When nearly the whole of the lead and other impurities have been absorbed by the porous cupel, the surface of the silver becomes iridescent, a phenomenon which is caused by very thin films of oxide of lead. Immediately afterwards the silver obtains a splendid, bright surface which serves as a sign of its purity. The metal is then cooled with water and taken away.
The process here described resembles closely, as already has been said, our cupellation method, the construction of the furnaces and especially its bottom being the only differences.
The ameliorated cupellation, known as Pattinton’s desilvering process, by which even minim quantities of silver can be extracted with advantage, is as yet unknown in Japan.
The amalgamation process, which is used on a large scale in Freiburg and in America, has found no practical application in Japan.
