;o2 



NATURE 



[September 8, 1910 



Hickson, Trof. S. J.— Table at the Zoological Slalion 



at Naples ••■ 25 



Waller, Prof. A. D. — Electromotive Phenomena in 



Plants 10 



Waller, Prof. A. D. — Anaesthetics 20 



Sherrington, Prof. C. S. — Mental and Muscular 



Fatigue 25 



Starling, Prof. E. H. — Dissociation of Oxy-ha;mo- 



globin ■ • 25 



Seciton K. — Botany. 



Scott, Dr. D. H.— Structure of Fossil Plants 15 



Darwin, Dr. F. — E.xperimental Study of Heredity 45 



Johnson, Prof. T. — Survey of Clare Island 20 



Oliver, Prof. F. W.— Registration of Botanical Photo- 

 graphs 10 



Section L. — Education. 



Findlay, Prof. J. J.— Mental and Physical Factors :o 



Corresponding Societies Committee. 

 Whitaktr, W. — For Preparation of Report 20 



Total 1090 



SECTION B. 



CHEMISTRY. 



Openi.no Address by J. E. Ste.ad, F.R.S., F.I.C., F.C.S., 

 President of the Section. 



It was with considerable diffidence that I accepted the 

 position of President of this section. The long list of 

 illustrious and eminent chemists who have occupied the 

 chair in the past, men of science of the highest attainments, 

 and usually professors of our educational institutions, is 

 indicative of the very high standard to be followed. As, 

 however, it was urged that a President with experience in 

 the metallurgy of iron and steel was desired, I bowed to 

 the decision of the Council, concluding that even as a mere 

 lavman I might, in this address, discuss one or more 

 subjects to which prominent metallurgists have for the past 

 thirty years directed their earnest attention, both in Europe 

 and America. I refer to some of the underlying phenomena 

 connected with the effect of sulphur and silicon on the 

 carbon condition of commercial cast iron. 



The effect of sulphur and silicon on cast iron has received 

 the attention of Karsten, Percy, Weston, Howe, Keep, 

 West, Dillner, Bachman, Summershach, Wiist. Johnson, 

 Stoughton, Hailstone, Longmuir, Adamson, Turner and 

 Schuler, Levy, and many others. They all agree in con- 

 cluding that sulphur tends to make iron white by retaining 

 the carbon in the combined state, and that silicon tends in 

 the opposite direction. Prof. Howe and Dr. Wiist have 

 endeavoured to arrive at the exact quantitative effect of 

 sulphur and silicon in preventing or facilitating the decom- 

 position of the carbides. 



Howe recognised that the data available are insufficient 

 on which to make any final conclusion. 



WCist found, by a series of trials, that in pigs containing 

 3' 15 per cent, carbon and about i per cent, silicon, on an 

 average 0*01 per cent, sulphur prevented the separation of 

 o'02 per cent, graphite, but that with 2 per cent, silicon its 

 effect was much less. 



It is the general experience, that the effect of sulphur 

 depends on the proportion, not only of silicon, but of the 

 total carbon and manganese, and of the temperature at 

 which the iron is cast, and the size and temperature of the 

 mould into which the metal is run. Under some critical 

 conditions 01 per cent, sulphur may prevent the separation 

 of 3 per cent, graphite. 



Howe's discovery — that the tendency of silicon, in in- 

 creasing the decomposition of the carbides, is rapid at first, 

 especially as the silicon rises from zero to o'75 per cent., 

 and then slower and slower with each further increase — is 

 very important ; so also is the generalisation of Messrs. 

 Charpv and Grenet — that the separation of graphite on 

 annealing iron which is initially white, containing the 

 whole of the carbon in the combined condition, begins at a 

 temperature which is the lower the greater the percentage 

 ef ihe associated silicon, and that the separation of 

 !.-raphite, once begun, continues at even lower temperatures 

 than that at which it started. 



NO. 2132, VOL. 84] 



The evidence advanced by Phillips, Prost, Campredon,. 

 -Schulte, and others — that, on dissolving sulphurous irons in 

 hydrochloric acid, all the sulphur is not given off as H,S, 

 and that a part either passes off as S(CHj), or remains 

 behind with the solution as some organic product — was 

 tentatively believed as indicative that the sulphur is 

 chemically associated with the carbon and the iron. 



Levy,' who has done much good work in the endeavour 

 to determine the relations which exist between iron, carbon, 

 and sulphur, in the alloys of these elements, states, as the 

 result of his research, that there is no conclusive evidence 

 of any chemical union. 



In his tabulated results showing the amount of sulphur 

 evolved presumably as S(CH3), on dissolving iron, carbon 

 and sulphur alloys, the maximum is o'o6 per cent., but the 

 average is very much less. 



Schulte, on the other hand, had found that from i per 

 cent, to 12 per cent, of the total sulphur is evolved as an 

 organic sulphur compound ; and Bischoff found an even 

 greater quantity. 



The results are apparently conflicting, and it is evidently 

 obvious that more research is required in this direction. 



It has been shown by ."Vrnold and McWilliam, and con- 

 firmed by others, that carbide of iron does not decompose 

 into graphite and iron during the annealing of steel until 

 it segregates into relatively large masses. Taking this as 

 a basis, Mr. Levy has advanced an explanatory hypothesis 

 as to how it is that sulphide of iron prevents the decom- 

 position of carbides in white irons. He had found that 

 during the solidification of irons free from silicon and 

 manganese, but rich in sulphur, " the sulphide separates at 

 a temperature in the neighbourhood of 1130° C, together 

 with, and as a component of, the austenite-cementite 

 eutectic, forming a triple austenite-cementite-sulphide 

 eutectic, the cementite component of which is interstratified 

 with a jointed pearlite (by decomposition of austenite) 

 sulphide one." He stated that "The presence of iron 

 sulphide in the eutectic introduces intervening layers, which 

 may partly ball up on annealing, but even then leave 

 sulphide films between the cementite crystals ; these act 

 almost as emulsiliers, preventing the coalescence of the 

 cementite portion, which is apparently a necessary pre- 

 liminary to its decomposition into free carbon and iron. 

 These layers and films are so persistent, even on slow 

 cooling, as to retain their position between the cementite 

 crystals, until the metal has cooled well below the tem- 

 perature of decomposition, so that an iron which might 

 otherwise become grey is retained, even on very protracted 

 cooling, in the white form, by sulphur as sulphide ; 0^25 

 per cent, sulphur being sufficient for this purpose under the 

 moderately protratced cooling conditions of the research. 

 It is not improbable that the mechanical force exerted by 

 sulphide, on separation and cooling, may also prevent the 

 physical conditions necessary for carbide decomposition, 

 which, as is well known, is accompanied by considerable 

 expansion." 



It is to be noted that Mr. Levy's argument is based on 

 the effect of the sulphide films in the eutectic, preventing 

 the segregation of the cementite into relatively large 

 masses, which, as he expresses it, " is apparently a 

 necessary preliminary to its decomposition." 



His conclusions were based on the examination of hypo- 

 eutectic alloys containing not more than 2"7^ per cent, 

 carbon and free from massive plates of cementite. 



Whilst admitting that his conclusions may be correct, as 

 applied to the eutectic, some other explanation would be 

 necessarv if decomposition did not occur when a consider- 

 able quantity of massive cementite initially were to form 

 in the alloy. 



That stable massive cementite can be so obtained in iron 

 sulnhide alloys I shall presently show. 



If it could be shown that sulphur in some form of com- 

 bination with the iron and carbon does crystallise with the 

 carbides, and that such mixture or solid solution is stable 

 and not readily decomposed, it would be reasonable to 

 conclude that the sulphur is responsible for the stability. 



It has been suggested that silicon in iron decomposes the 

 carbides according to the following chemical reaction : 

 3Si-=Fe,C = 'Fe,Si-2C. The onlv objection to this ex- 

 planation is that the silicon is not free in cast iron, as was 



•J" 



igof. 



