Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/367

IRON 351 reduced and contained in the final alloy is exerted by silica ; if much of that substance be present the product is comparatively poor in manganese, a green slag (mainly manganese silicate) being formed ; a very high temperature too is essential ; of late years blast furnace manganeisens have almost superseded these open hearth products. Alloys containing 25, 50, 75, and even more per cent, of man ganese are usually employed in the manufacture of so-called extra soft steels (or more properly fused irons), the use of spiegeleisen being in such cases inadmissible inasmuch as too high a degree of carbonization would be effected if sufficient .spiegeleisen were added to communicate as much manganese as is desired to be present ; thus at Terre Noire, where the preparation of ferro-manganese has been extensively experimented with and adopted, only about 1 5 parts of 45 per cent, manganeisen are added to 100 of the decarbonized product from the Siemens- Martin hearth or Bessemer converter, thus communicating some 07 per cent, of manganese with less than O l per cent, of carbon ; whereas were spiegeleisen used at 8 per cent, manganese only, either the carbon percentage would be far too great, or the manganese would be too low to give the particular physical qualities required. For the manu facture of spiegeleisen the franklinite of New Jersey (essentially a compound of ferric oxide with oxides of zinc and manganese) has been long utilized, being first heated with anthracite so as to reduce and distil off most of the zinc (the vapour of which is allowed to oxidize, the resulting oxide being collected), and then smelted in small blast furnaces with anthracite and limestone flux with a large excess of fuel (about three times the weight of spiegeleisen run or more). According to Snelus (Journ. I. and S. List., 1874, C8) the best results are obtained when a certain quantity of manganese remains unreduced and escapes in the slag, which should have about the following composition to give the best results : Silica 35 per cent. Alumina 10 ,, Lime 30 , , Manganous oxide 12-20 ,, constituting a green vitreous smooth mass of conchoidal fracture. The composition of the charges introduced into the furnace must be calculated out so as to give about this amount of manganese unreduced together with that reduced in relation to the other con stituents respectively ; thus from the following average composition of charge the annexed slag and spiegeleisen result : Charge. Slag. Si>iegelcisen. Per cent. Silica 14 Per cent. 33 Iron. 83 08 Alumina 6 14 6 Manganese 12 30 Manganese oxide 16 - 5 16 Carbon 3 90 Lime and magnesia 3 32-0 Silicon 54 Ferric oxide 47 Sulphur trace Phosphorus 08 99-90 Much more richly manganiferous metals than this have been obtained in the blast furnace by W. G. Ward (Cartersville, Georgia) by simply increasing the amount of lime added, and employing a smaller burden ; in this way ferro-manganese of upAvards of 50 per cent, has been manufactured readily, about three-fifths of the man ganese in the charge being reduced. Analogous metals have been obtained by many other smelters; thus specimens of ferro-manganese containing upwards of 80 per cent, of manganese and prepared in the blast furnace were exhibited in the Paris exhibition. According to Akermann, to produce ferro-manganese of 85 per cent, in the blast furnace is a matter of no great difficulty, but the consumption of coke is about four times greater than that required for common pig iron, whilst the daily output is only about one-fourth of that of the latter. No advantage attends the production of manganeisen of upwards of about 80 percent., but rather the contrary, richer metal being very brittle. It is noteworthy that, notwithstanding the use of much more fuel in a furnace smelting rich manganeisen, the escap ing gases do not contain more carbon oxide than (and often not as much as) those of an ordinary blast furnace, the extra oxygen in the carbon dioxide escaping coming from the higher oxides of man ganese employed as manganese ores. A description of the older modes of producing spiegeleisen in Germany is given in a report by Wiborg to the Swedish iron office (Jern-Kontorets Annalcr, 1870 ; also in abstract in Journal I. and S. Tnst., 1872, 138). When lime fluxes are employed, it is indispensable that they should not contain phosphorus ; thus the spiegeleisen prepared in New Jersey from franklinite was found to contain phosphorus to a decidedly prejudicial extent when oyster shells were employed as flux, but ceased to do so when good limestone was used instead. It is noteworthy, however, that when a highly manganiferous iron is smelted a considerably larger preparation of phosphorus finds its way into the cinder and less into the pig than is the case when the resulting pig contains lees manganese ; and the same remark is also largely true of sulphur. According to several chemists and metallurgists as the percentage of manganese in manganeisen increases, so, roughly speaking, that of carbon decreases ; so that whilst spiegeleisen of 7 or 8 per cent, manganese usually contains some 4 or 5 per cent, of carbon and sometimes more, ferro- manganese of 20 per cent, manganese contains much less carbon, and when the manganese attains to 30 per cent, and upwards the carbon becomes diminished to something below 1 per cent., being often as low as 04 or even 25 per cent. (Henderson). Others, however, have obtained diametrically opposite results ; thus Eiley and Griiner both find that the carbon percentage increases pari passu with that of manganese. The peculiar large mirror-like crystals from which the term "spiegeleisen " (mirror iron) is derived are not exhibited by ferro-manganese containing large amounts of manganese. By mixing finely divided iron (sponge, filings, turnings of cast or wrought iron or steel, &c.) with finely powdered ores of manganese, tungsten, or titanium, or with quartz in suitable quantity, moistening with dilute acid or ammoniacal solution, and compressing into lumps, hard masses are formed (after standing a few hours) which can be heated to a red heat without breaking up. By melting these in a small cupola furnace with a crucible or hearth of alumina, magnesia, or lime, or of hard carbon and a tuyere letting in a hot blast just above the top of the hearth, manganeisens and siliconeisens containing up to 75 per cent, of manganese or 22 per cent, of silicon, or iron-tungsten or iron-titanium alloys, or ternary alloys can be readily produced (Ghronique de I Industrie, 1873, ii. 235). The following analyses illustrate the composition of various kinds of spiegeleisen, ferro-manganese, and allied products: English Spiegel eisen. New Jersey Spiegel- eison. Frank- iinite. Mtisen Spiegel eisen. Ferro- man ganese. Reschitza, Hungary. Chrom- eisen. Titnni- ferous Pig. Ilmanite and Hae matite. Riler JJiley Iron 75-96 88-30 82-8CO 23-46 87 S 93-47 "Combined" carbon Graphite C-23 1 5-43 4-323 6-21 ( 2-82 } 831 Silicon .. 0-37 0-20 i-ooo 28 21 1-86 Manganese 18-36 4 50 10-707 G9-G4 50 nil 0-08 0-014 0-06 Phosphorus 06 0-15 0-059 06 0-12 008 Zinc 0-30 Copper O OGG 0-14 Chromium 8 57 Titanium 0-006 i ifl Nickel and cobalt... Calcium, magne sium, aluminium, arsenic, &c., and loss ( : 0-018 0-J49 100-00 90-01 100-000 99-79 100-00 100-43 Siliconcisen. In order to produce highly silicious iron, accord ing to Jordan, the main conditions are that the blast shall be extremely hot, the furnace not driving rapidly, and that the charge whilst containing much silica shall be highly aluminous and not markedly calcareous. An accident at the Heardt iron-works, Diisseldorf, necessitated the shutting off of the majority of the blast, three tuyeres instead of six being used, and the pressure- being reduced from 15-18 to about 10 centimetres of mercury (i.e., from about 3 1 to 1 9 K> per square inch) ; the blast became highly heated (from 500 to 600 C.), whilst the burden was increased, the charge containing 12| cwts. ore at 38 per cent, iron, 6 cwts. limestone, and 10 cwts. coke, so that the slag contained silica 50, lime 33, alumina 16, manganese oxide 1, the coke being 42 cwts. per ton of iron. Under these conditions a pig was run containing silicon 7 9, phosphorus 072, and carbon 2 -60 per cent. Analogous results as regards increased percentage of silicon on decreasing lime and increas ing alumina relatively to the silicon have been observed in various other instances. Troost and Hautefeuille consider that the presence of alkaline silicates in the furnace promotes the siliconizing of the iron, the alkali metals formed at a high temperature by the reduc tion of the alkalies reacting whilst still nascent on the silica, and thus reducing it ; a mixture of potassium carbonate, charcoal, iron