Lead-Smelting

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: long trains of these, representing many tons of molten slag. By making 10 per cent. matte extremely impure and refractory ores can be treated with greater success. While 10 per cent. matte is desirable in most cases it should not arbitrarily be followed. From 4 to 7 per cent. is sometimes sufficient,...
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Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: long trains of these, representing many tons of molten slag. By making 10 per cent. matte extremely impure and refractory ores can be treated with greater success. While 10 per cent. matte is desirable in most cases it should not arbitrarily be followed. From 4 to 7 per cent. is sometimes sufficient, especially when treating pure silicious ores and where the barium sulphate is nearly absent. There are times when it is impossible to keep the yield of matte below 12 to 15 per cent. for short periods. MAGNETIC SLAGS. It has been found that many lead slags, even though free from matte globules, are not to any degree magnetic, particularly ij powdered in an agate' or Wedgwood mortar. The rubbing off of the iron of the bucking plate and muller imparts the supposed magnetability to these slags. In copper metallurgy, where the roasted ore is melted down, producing a first matte and a slag running 40 per cent. silica, it has been shown to be magnetic and it is assumed that a portion of the iron exists in the form of magnetic oxide. MAGNESIA. Once it was thought magnesia was a source of much trouble. Great stress was laid on the high fusing-point of the silicate. This temperature called for an increase of fuel and silver losses were supposed to be high; the mixture of zinc with magnesia was believed to be specially injurious. Experience taught that magnesia gives little trouble when intelligently handled. Magnesia is a strong alkaline base, stronger than lime and four times stronger than baryta; it unites readily with silica, and when this silicate alone is formed the temperature employed is rather high, but when in the presence of a number of other bases it does not materially increase the fusing-point of a slag. As it saturates much silica the quantity of limestone required...