This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1906 edition. Excerpt: ...strip of iron to decompose the sulphide or arsenide present. But this omission may be remedied by adding iron to the mixture used for cleaning the slag. The slag is generally glassy, but varies with the nature of the ore, and should be uniform in colour and composition. (6) Cleaning the Slag.--The slag ...
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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1906 edition. Excerpt: ...strip of iron to decompose the sulphide or arsenide present. But this omission may be remedied by adding iron to the mixture used for cleaning the slag. The slag is generally glassy, but varies with the nature of the ore, and should be uniform in colour and composition. (6) Cleaning the Slag.--The slag is pounded in a mortar covered with a duster to prevent loss, and mixed with 300 grains red lead, 15 grains charcoal, and 20 grains carbonate of soda. Fuse for about fifteeen minutes in the same crucible in which the ore was smelted, and pour into round mould as before. The slag obtained in this case is thrown away, and the lead button after cleaning saved for cupellation. (c) The two lead buttons are then cupelled, particulars of which have been given in 124. 129. (a) Sulphides of copper, iron, lead, etc., containing silver, may also be assayed by the crucible method just described; but the sulphur, arsenic, etc., must be oxidised by a preliminary roasting, or a large quantity of red lead must be added in the fusion mixture. The oxidation is effected by heating the powdered ore at a low temperature at first, in a roasting dish made of fire clay, constantly stirring with an iron rod, as the material, especially in the presence of lead, has a great tendency to fuse and clot together, which prevents oxidation to a great extent. In about fifteen minutes the greater part of the volatile matters will be expelled, and the temperature may then be raised to complete the operation. (6) The quantity taken for roasting should vary with the richness of the ore, but the following may be taken as an average sample. Take 200 grains and roast as above, then mix with red lead, 1000 grains; charcoal, 35 grains; borax, 400 grains; and carbonate...
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