IRON 981 



had combined with the iron, when the action ceased. If the charcoal be very strongly 

 ignited previous to the experiment, the carbonisation of the iron does not take place, 

 neither does pure carbonic oxide carbonise iron when passed over the metal at a red 

 heat : the effect in the experiment above described may therefore be due to the 

 carburetted hydrogen evolved from the charcoal. Iron begins to take up carbon 

 when heated only to the softening-point, the carbon gradually penetrates the metal, 

 converting it first into steel and then into cast iron ; conversely melted cast iron gives 

 up carbon to soft iron, which it converts into steel. When white iron (Fe*C) is 

 heated with acids, nearly the whole of the carbon is eliminated in combination with 

 hydrogen. Grey iron only gives up to hydrogen the carbon which was chemically 

 combined with the iron, the uncombined carbon or graphite remains unacted upon ; 

 the dark spot produced upon grey iron by a drop of nitric acid arises from this sepa- 

 ration of graphite. For the amounts of carbon in the different varieties of steel, see 

 STEEL. 



Phosphorus. In very few specimens of crude iron is this element wholly absent ; 

 when it exists in small quantities only, it is said rather to improve the iron for 

 castings, as it imparts to the metal the property of fusing tranquilly ; in a larger 

 proportion, it weakens the iron. In like manner a very small quantity of phosphorus 

 hardens bar iron, without materially influencing the other properties, but when it 

 exceeds '5 per cent, it renders the bar brittle, cold-short, as it is termed. According 

 to Schaf haeutl, both cast iron and steel are improved by phosphorus and by arsenic ; 

 he found the latter in the celebrated Dannemora iron, and in the Lowmoor iron, and 

 the former in the equally famous Kussian (CCND) iron. 



Sulphur. This element imparts to crude iron the property of becoming viscid, and 

 of solidifying quickly with cavities and air-bubbles. It is not certain to what extent, 

 or if at all, the presence of minute proportions of sulphur reduces either the tenacity 

 or the toughness of cast iron of given quality in other respects. It is stated in tho 

 Keport of the Commission of Inquiry, as to the manufacture of ordnance on the 

 Continent, on the authority of Schiir and Mitscherlich, that in certain Swedish works 

 pyrites is thrown into the furnace, with the other constituents of the charge, to pro- 

 duce the fine grey mottled iron required for gun founding, and it is added that the 

 effect may be analogous to that of the oxidising flame in a reverberatory-furnace. It 

 is certain that sulphur possesses the property of concentrating carbon in iron : and as 

 mottled iron is a mixture of white and grey iron, it is not difficult to see how the 

 addition of pyrites may determine the formation of this variety of cast iron in a 

 furnace, which without it would produce grey iron only : but it is scarcely credible 

 that any intelligent founder would resort to such a method of making iron for casting 

 cannon, in which the highest possible degree of tenacity is required. The fine grey 

 mottled iron, which from its tenacity is known to be best fitted for large castings, is 

 said to be prepared without difficulty, by charging the furnace partly with roasted 

 and partly with raw ore, and so regulating the blast that the yield shall be regular, 

 and the slag nearly colourless : these two ores, having different degrees of fusibility, 

 are reduced after different periods in the furnace, and hence afford one of them grey, 

 and the other white iron ; the result being, provided the minerals are properly pro- 

 portioned, a mottled iron, harder and more tenacious than grey iron, obtained by 

 mixing or smelting in the cupola. It is desirable that the temperature of the furnace 

 should be kept as low as possible, the production of dark grey graphitic iron resulting 

 always from intensity of heat* 



When sulphur is melted with iron containing the largest amount of chemically- 

 combined carbon, sulphuret of iron is formed on the surface ; underneath, a layer of 

 graphite, and beneath that, a layer of iron with the maximum of carbon ; and when 

 grey iron containing 3'31 per cent, of graphite is melted with sulphur, white iron 

 (containing 94'03 iron, 4*93 combined carbon, and no graphite), is formed. The ten- 

 dency of sulphurous ores to produce white metal in their treatment in the blast-furnace 

 has long been known. It was supposed that this was occasioned by the too great fusi- 

 bility which the sulphur gave to the cast iron ; but ores containing large proportions of 

 phosphoric acid will produce very grey iron, notwithstanding their fusibility, so that 

 this explanation does not serve : the experiments above described point to the true 

 reason. The sulphur present in the ore (if as sulphuric acid reduced in the furnace) 

 enters into combination with the iron, displacing a corresponding proportion of carbon, 

 which becomes concentrated in the remainder of the metal, forming white iron. To 

 guard against this, and in order to obtain a metal which shall contain a minimum 

 amount of sulphur, the slags should contain the maximum amount of lime, M. Berthier 

 having shown that this earth decomposes sulphuret of iron at a high temperature, in 

 the presence of carbon. M. Janoyer states that the proportion of lime and silica in 

 the slag may be as 54 to 36 : it is doubtful whether such a highly basic cinder would 

 be sufficiently fusible. Direct experiments, however, have shown that the amount 



