A text-book of inorganic chemistry / by G.S. Newth.

  • Newth, G. S. (George Samuel)
Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: A text-book of inorganic chemistry / by G.S. Newth. Source: Wellcome Collection.

    648/718 (page 626)
    as it descends, until it passes from a pasty condition to a state of complete fusion, when it collects upon the bottom, or hearth, of the furnace. In passing through the hottest regions, the lime combines with the siliceous materials originally present in the ore, to form a fusible slag, beneath which the molten iron collects. Other re- actions which go on in various regions of the furnace, are the reduc- tion of sulphur compounds, and of phosphates and silicates, with the absorption into the iron of a certain amount of sulphur, phos- phorus, and silicon. The precise nature of the changes suffered by the gases in the various regions of the furnace, is still obscure. The cyanogen formed by the direct union of atmospheric nitrogen with carbon, and also the hydrocarbons present, doubtless undergo a chemical change in contact with the heated iron, and probably ^ aid in its carburisation. The molten iron is drawn off at intervals from a tap-hole into moulds, and is known as cast iron ox pig iron. The slag as it accumulates, overflows in a regular stream through an opening known as the slag hole. When such a furnace is in full blast, fresh charges of materials are introduced at regular intervals, and the process continues uninterruptedly for years. The metal • obtained from the blast-furnace is far from pure iron, but contains varying quantities of carbon, silicon, phosphorus, sulphur, and manganese. The carbon may be present either in combination with iron as a carbide, or distributed throughout the metal as fine particles of graphite, or in both of these forms. White cast iron contains its carbon in the combined fonn, while grey cast iron owes it grey y colour to the presence of minute ciystals of graphite disseminated ^ throughout the metal. When grey cast iron is dissolved in hydro- chloric acid, the graphite remains behind as a black powder ; but £ on similarly treating iron containing co7nbined carbo7i, the carbon g unites with the hydrogen, forming various hydrocarbons, which 2 impart to the escaping gas a characteristic and unpleasant smell. * Average cast iron contains from 90 to 95 per cent, of iron, and 3 to 5 per cent, of carbon. Spiegel is a variety of white cast iron con- Y taining 3.5 to 6 per cent, of carbon, and from 5 to 20 per cent, of S manganese. With more than 20 per cent, of manganese, the metal is termed ferro-77ia7iganese. ^ Purification.—The properties of iron are greatly modified by the presence of various impurities, especially carbon, and for ■ different purposes for which iion is used, metal of different degrees of purity is required. The purest form of ordinary commercial*