The following are some of the causes of brittle gold, (a) Oxidation of copper and absorption of the copper oxide by the molten metal, (b) A pasty condition of the molten metal at the moment it is poured into the mould or ingot, (c) The mould may be too hot or too cold at the time of pouring the metal. (d) Absorption of some impurity from the flux, (e) Some impurity in the added copper or silver. The impurities in added metals may be arsenic, phosphorus, iron, or nickel in the copper; lead or zinc in the silver. Impurities in the flux may be grit and iron in the sal-ammoniac, and tree mercury in the corrosive sublimate. In melting the metals for 18-carat gold, use a plumbago crucible lined with finely powdered charcoal and put the copper in first, then add the silver and gold. When the mixture is at the point of fusion, throw on its surface about two tablespoonfuls of tiuefy powdered vegetable charcoal and finely powdered best sal-ammoniac intimately mixed. Use no other flux. When completely fused, stir the whole with the point of a red-hot iron rod, bring to the proper fluid condition for pouring, and hold a strip of wood to the mouth of the crucible to keep back loose flux whilst pouring the metal into the mould.