122 SUMMABY OF CURRENT RESEARCHES RELATING TO 



any point in which represents the composition of an alloy. The dia- 

 gram of the iron-manganese-carbon system is shown in this manner. 

 The iron-phosphorns-carbon system, considered as a ternary system the 

 components of which are iron, iron phosphide and iron carbide, resembles 

 the lead-tin-bismuth system. Alloys of iron and carbon with a third 

 element follow one of two types: — 1. The iron -carbon-manganese 

 system. The third element forms solid solutions with both y-iron and 

 iron carbide. Systems following this type are Fe-Cr-C, Fe-W-C, 

 Fe-Xi-C, Fe-Si-C. 2. The iron-carbon-phosphorus system. The third 

 element forms a chemical compound with iron, and the compound is 

 insoluble in iron carbide, and insoluble or partly soluble in y-iron. To 

 this type belong Fe-P-C, Fe-Sn-C. Fe-As-C, Fe-Sb-C. 

 Useful bibliographies are appended to both these papers. 



Cementation by Carbon.* — L. Guillet and C. Griffith have made 

 careful cementation experiments on iron and low-carbon steel. Samples 

 buried in powdered purified sugar-carbon and heated at 1000° C. in a 

 porcelain tube in which a vacuum was maintained showed a small 

 increase in carbon content, but when the metal and carbon were both 

 previously heated separately to expel occluded gases, a similar " cemen- 

 tation " gave no increase in carbon. The effect of pressure, slight or 

 great, was also studied. The chemical analyses were checked by micro- 

 scopic examination, which gave information as to the distribution of 

 carbon absorbed by the metal. The authors conclude that pure carbon 

 cannot be absorbed by iron when heated in a vacuum, unless contact be 

 assured by mechanical means, or dissolved gases be present. Cementation 

 increases with increase of pressure. 



Constituents of Steel. — The definitions adopted by the Copenhagen 

 Congress of the International Association for Testing Materials! are 

 given. A " metaral " is a chemically homogeneous constituent, an 

 " aggregate " is a chemically heterogeneous constituent. The metarals 

 are ferrite, graphite, cementite, austenite, and martensite. Pearlite, and 

 possibly osmondite, are aggregates. Martensite is defined as a solid 

 solution of carbon and iron, not stable at any temperature, distinguish- 

 able from austenite by its greater hardness and magnetic permeability. 



H. le Chatelier| discusses the definitions, and explains the replace- 

 ment of the name " troostite " by " osmondite," and the omission of 

 " sorbite." 



F. Osmond§ does not agree to the abandonment of " sorbite " and 

 the replacement of " troostite " by " osmondite." 



Metallography of Iron.|| — H. M. Howe considers that the results 

 obtained by Baykoff IT have made possible a simplification of the theory 

 of the iron-carbon system. The. needle structure of martensite now 

 appears to be characteristic of /3-iron, not of a crystallitic form of y-iron. 

 The author collects the evidence that the martensite needles represent a 

 stage intermediate between y- and a-iron. The specific volume, brittle- 

 ness and hardness corresponding to the needle structure are all greater 



* Eev. Metallurgie, vi. (1909) pp. 1013-23 (3 figs.). t Tom. cit., pp. 1122-3. 

 J Tom. cit., pp. 1124-6, 1366. - § Tom. cit., pp. 1183-7, 1363-5. 



|j Electrochem. and Met. Ind., vii. (1909) pp. 423-7 (5 figs.). 

 i See this Journal, 1909, p. 669. 



