Thirty-eighth annual report [of the] Local Government Board. Supplement in continuation of the report of the Medical Officer of the Board for 1908-09, containing Reports and papers on the nature, uses and manufacture of ferro-silicon, with special reference to possible danger arising from its transport and storage / by S. Monckton Copeman, Samuel R. Bennett and H. Wilson Hake.

Date:
1909
Catalogue details

Licence: In copyright

Credit: Thirty-eighth annual report [of the] Local Government Board. Supplement in continuation of the report of the Medical Officer of the Board for 1908-09, containing Reports and papers on the nature, uses and manufacture of ferro-silicon, with special reference to possible danger arising from its transport and storage / by S. Monckton Copeman, Samuel R. Bennett and H. Wilson Hake. Source: Wellcome Collection.

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    pounds which would produce them in contact with water, are likely to be formed in the process of manufacture of ferro-silicon. Dr. Copeman has described this process of manufacture after personal inspection of many factories. To briefly recapitulate liis statement, a mixture of steel turnings obtained from gun foun- dries, together with quartz and coal from neighbouring mines, is put into an electric furnace of a capacity of about 1,500 kilo- grammes and heated to a temperature roughly computed at from 1,800° to 2,000° C. The quantities of quartz (which contains about 96 per cent, of silica or silicon dioxide, Si02) and anthracite coal (containing about 90 per cent, of carbon and 10 per cent, of ash) are always used in the proportion of one molecule of silica to two atoms of carbon so that complete reduction of the former to silicon (Si) shall occur, according to the chemical equation :— Si02 + 2C — Si + 2CO. The proportion of iron taken, varies and depends on the grade of ferro-silicon required, that is, on the desired percentage of silicon in the alloy ultimately produced. Certain impurities originally present in the coal, iron and quartz used, or formed from them during the process of manufac- ture, are always present, and some of these, although amounting to a very small percentage of the finished product, are the ulti- mate cause of the serious mishaps which have arisen from the extended use of ferro-silicon. Calcium phosphate [Ca3 (P04)2], one of the impurities present in coal and in quartz,* which in itself is a perfectly harmless salt, insoluble in water and widely diffused in nature, is responsible for the production of a dangerous compound by reduction in the electric furnace, in the presence of carbon, to calcium phosphide (Ca3P2). This calcium phosphide remains in the ferro-silicon, and in contact with water or moist air is decomposed with evolu- tion of phosphoretted hydrogen (PH3), the intensely poisonous character of which has been referred to above. Arsenic again, an element closely allied to phosphorus in its properties, is another impurity liable to be present in various com- binations in coal and in iron, and this element also finds its way into the ferro-silicon apparently as calcium arsenide. Calcium arsenide is also decomposed by water or moist air, evolving arseniuretted hydrogen (AsH3), a gas scarcely, if at all, less poisonous than phosphoretted hydrogen. Acetylene (C2H2), which is not commonly regarded as poisonous unless present in large proportion in air, would be evolved by the action of moisture on ferro-silicon if calcium carbide (CaC2) were present as an impurity, since this substance also is decomposed by water with formation of lime (CaO) and evolution of acetylene. But the presence of calcium carbide is improbable seeing that lime, as a flux, is not now used in the manufacture of ferro-silicon. It lias been stated by certain writers that lime was formerly used as a flux in making ferro-silicon, but if so its use has now * I examined three samples of quartz and three samples of coal or coke used by various manufacturers of ferro-silicon and found calcium phosphate in considerable quantities in all of them.