Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/312

 296 IRON together, with the addition of a little limestone or quick lime, furnish a cinder consisting mainly of calcareous aluminium silicate which readily melts and separates from the pig iron; similarly aluminous shales from the Coal Measures may be used instead of bauxite, whilst certain Swedish ores naturally containing as gangue fusible silicates of lime and magnesia, together with limestone, can be smelted without any additional flux of any kind, and will even serve to take up the silicious gangue from other ores when smelted with them if the latter are not in too large a proportion. On the other hand, clay ironstone and clayey ores generally usually require a considerable admixture of limestone or quicklime in order to yield a sufficiently fusible cinder, the presence of a sufficiently large amount of basic matter (lime and magnesia, or manganese oxide) in the cinder being essential in order to prevent the pig iron from taking up too much sulphur from the coke or coal when these fuels are employed. Phosphorus, however, when present in either the ore, the flux, or the fuel, is almost entirely taken up by the pig iron, as was shown in 1838 by Berthier, and subsequently confirmed by other observers ; thus Lowthian Bell found that in a furnace smelting Cleveland ironstone, with a con sumption per 100 parts of pig of Ironstone containing 522 per cent, of phosphorus -=240 parts Limestone ,, O Oll ,, ,, 60 ,, Coke ,, 0-265 ,, -120 and a formation of 150 parts of cinder containing 098 per cent, of phosphorus, the amounts of phosphorus leaving the furnace in the slag and pig iron respectively were almost exactly 10 and 90 per cent, of the total phosphorus present ; whilst in the same series of experiments the sul phur retained by the iron and that passing out in the slag were respectively between 2 and 2 5 and between 97 5 and 98 per cent, of the total sulphur present (which amounted to upwards of 4 parts per 100 of pig). According to Riley the amount of phosphorus retained in the slag is greater the more iron is present. When the reduction of the metal is all but complete, and the furnace consequently is working well, the pig contains practically all the phosphorus pre sent, whether it be white or grey ; but if the slag becomes more or less of a &quot;scouring&quot; character through incomplete reduction of considerable amounts of iron, notable quantities of phosphorus are also present therein. &quot;VVitherbeo finds that a certain small amount of phosphorus contained in the charge fails to appear in the pig iron, this amount being greater the higher the temperature of the hearth, i.e., being greater when Bessemer pig is being run than with iron smelted at a lower temperature. This he explains by supposing that phosphorus is volatilized in the furnace, a view apparently cor roborated by direct experiments made by Akermann. Some of the Lincolnshire ores are imbedded in a calcareous matrix or gangue ; in order to smelt these an admixture of silicious ore is necessary. For this purpose the more or less silicated forgo mill cinders from the manufacture of malleable iron are frequently used, these substances virtually constituting rich iron ores, the only draw- l&amp;gt;ack of which is that their texture is compact, and they generally are in small pieces, so that they could not be smelted advantageously alone; moreover, they usually contain considerable quantities of phosphorus, if that constituent was present to any extent in the original pig used for puddling, mill cinder (the scale formed and detached during rolling) being much purer in this respect than forge cinder (the molten slag squirted out during hammering). When any notable amount of manganese oxide is present in the cinder, it is generally very fluid and easily fusible; accordingly, when a furnace shows a tendency to &quot;scaffold&quot; (by the fritting together of lumps which form a comparatively solid skeleton mass inside the furnace, preventing the charge from descending properly), a mangani- ferous ore is sometimes employed as a sort of flux to assist in remov ing the obstruction by melting it down. In Sweden, when sulphur is present in the ores to an undue amount (through imperfect cal cination, &c.), it is usual to add some titaniferous ore to the charge (some 10 per cent, or so) ; the pig is thereby prevented from taking up the sulphur, possibly through the formation of titanium snlpho- cyanide. In the anthracite furnaces at Cedar Point, U.S., it was found that a much more fluid cinder was produced when a magnesian limestone, containing 67 per cent, carbonate of lime and 27 per cent, carbonate of magnesia, was used than with ordinary limestone of 95 per cent, carbonate of lime, other things being the same. As a general rule it may be said that the composition of the cinder from a blast furnace working satisfactorily varies between that of an orthosilicate, 2RO,Si0 2 or 2R 2 O 3 ,3Si0 2, in which the oxygen of the bases present is equal to that of the silicon dioxide, and that of a metasili- cate, RO,Si0 2 or R 2 3 ,3SiO 2, in which the oxygen of the bases is one half of that of the silicon dioxide, the dyad metals being essentially calcium and magnesium, and with certain ores manganese, whilst the triad metals are usually only represented by aluminium. More or less ferrous oxide is, however, invariably present ; cseteris pariliis, the darker the colour of the slag the more iron it contains. When the furnace is working properly the amount of ferrous oxide is small, not exceeding 1 or 2 per cent, of the cinder ; but when the reduction of the iron is imperfect, and a &quot; scour ing cinder &quot; is being produced, the quantity of ferrous oxide present may amount to one-fifth or more of the cinder, representing a very large loss of metal. The follow ing analyses represent the composition of various kinds of limestones and other fluxes employed : Calcareous Fluxes. Character of Flux and Locality.... 1 I Moun tain Lime stone, Skipton. Durham Lime stone, Wear- dale. Crystal line Lime stone, Spring- tield. Undrlfd Surrey Chalk. Oyster Shells from Chesa peake Bay.i Anker- it , London derry, Nova Scotia. Riley. Abel. Abel. Clap- Lowthian Cliap- Calcium carbonate .... Magnesium 98-17 1-17 036 9-55 3-20 trite* 88-85 2-03 1-21 78-00 trace 94-48 0-94 51-24 23-23 24-46 Manganese trace 0-15 0-22

0-98 Calcium sulphate ,, phosphate ... 0-03 traces 0-12 6-20 0-24 12 0-33 0-80 0-OG Silica and matters) insoluble in acids} Organic matter Water 0-28 trace* 013 0-90 0-23 8-15 trace o-co 20-00 2-54 0-04 Soda 0-16&quot; 6-63 100-14 100-00 100-50 100-62 100-00 100-00 Used in Baltimore furnaces as flux. - As sodium chloride. Aluminous and Magnesian Fluxes. Charicter of Flux ( and Locality 1 Bauxites from I5aux, France Bauxite, Belfast. Pisolitic Aluminous Iron Ore, Red Bay, Antrim. Coal- im-asure Shale, Lanca shire. Variety of Horn blende used in Sweden as Flux. Deviile. Ritchie. Crossley. Frank- land. Ramm els- berg.; 58-1 3-0 30-3 34-9 41-30 2S-74 0-78 20-37 71-63 0-68 21-73 4 ; 73 1-77 Ferrous Lime trace 1-70 0-23 14-05 o-oi o-oi 13-85 0-30 trace trace c-oo 1-lfl 0-73 6-09 059 61-91 7-43 11-00 28-19 58-86 0-18 Silica 21-7 14-0 221 Phosphoric anhydride... Sulphuric Water and orRanic^ 12-7 3-41 100-0 1 100-0 100-97 100-38 9989 100-00 Effects of Calcination of Limestone. When quicklime, or cal cined limestone, is employed instead of raw limestone, a certain diminution in the amount of fuel requisite to run a given quality of pig with a given furnace is noticed, arising from the circum stance that in calcining limestone heat is absorbed, so that when quicklime is used there is a less demand on the heat developed in the furnace than with raw limestone. The saving in this way, however, is rarely equal to the amount of fuel used in the limekiln itoelf, probably because in the top portion of the furnace the quick lime becomes partially recarbonated by the escaping gases. When the amount of limestone used is large, the carbon dioxide intro duced into the furnace in that form is a large fraction of the total carbon dioxide expelled in the escaping gases, and consequently the carbon of the fuel cannot be burnt to so great an advantage as it