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PHYSICAL ELEMENTS IN CHILLING CASTINGS. 261
than does sulphur. It is claimed that this same effect is caused by the use of low phosphorus iron, and is so radical that it makes the interlacing of the grey and chilled bodies very pronounced, as shown in Fig. 57, page 264. In referring again to manganese, it can be said that its effect to harden is often partly neutralized by the sulphur it expels, hence its power to increase hardness may sometimes be very small and often call for a large increase of manganese before it can produce any pronounced effect.
Professor Ledebur's division of carbon into four states, wherein he describes the elements (as seen in Table 44, page 267) existing in carbon as hardening, carbide, graphitic, and temper-carbon, is a factor that some believe may account, in some cases, for like depths of chill not presenting like degrees of hardness, also to account for other qualities in physical effects which at present are not clearly defined. The professor treated this subject in a paper before the Iron and Steel Institute, found in their Proceedings, No. 2, 1893. Some are of the opinion that the differences seen iii the grain of charcoal from coke iron, although the former may carry higher graphitic carbon, is due to there being a relatively larger per cent, of graphitic temper-carbon in charcoal than in coke iron, which is formed while the carbon is in a transition state toward graphite. It is unfortunate, as stated by Professor Ledebur, that there is no known method of analyzing graphitic temper-carbon, or that it can only be determined by being estimated with the graphite. If this could be determined there would be much more interest taken to note its effect in castings.ulphur.