386 SUMMARY OF CURRENT RESEARCHES RELATING TO 



metals of undoubted crystalline structure are plastic within certain 

 ranges of temperature. If a plastic crystal be cut in two, each portion 

 assumes the form of the original crystal. Two plastic crystals in con- 

 tact frequently combine to form one crystal. It is possible to deform a 

 plastic crystal without changing its orientation. The theories of 

 Lehmann, Tammann, and others, as to the nature of doubly-refracting 

 liquids, are briefly stated. 



H. le Chatelier * points out that the growth of metallic crystals at 

 certain temperatures, and also the capacity exhibited by some metallic 

 crystals of being deformed without change in crystalline orientation, 

 are exactly the same phenomena as those observed in the plastic crystals 

 referred to above. As the method of examination by polarised light 

 cannot be employed for the study of metals, since they are not trans- 

 parent, it is hoped that the researches now being conducted upon soft 

 crystals of organic bodies may throw light on the constitution of 

 malleable metals. 



Recent Researches upon Industrial Alloys.f — L. Guillet reviews 

 the work carried out on alloys during the last few years. A classifica- 

 tion of binary alloys is given, based upon the capacity of the two metals 

 to form either definite compounds, or solutions of one metal in the 

 other, both in the liquid and solid states. The importance of solid 

 solutions is insisted upon. A concise account of methods used in the 

 investigation of alloys is given. The most important of these methods 

 is microscopical examination of prepared sections, which has the advan- 

 tages of being rapid and inexpensive. Information of great value may 

 be obtained by a study of a complete freezing point curve. The author 

 proceeds to deal with a large number of alloys in some detail ; among 

 those considered are the iron-carbon series and the special steels, the 

 alloys of copper with tin, phosphorus, aluminium, nickel, silicon, vana- 

 dium, chromium, tungsten, etc., the antifriction alloys, and the 

 aluminium-manganese alloys, some of which are magnetic. The refine- 

 ment of methods of determining thermal changes upon heating or 

 cooling, has led to the discovery of transformation points in the bronzes 

 and other alloys. 



Quenching of Steel.! — A. le Chatelier discusses a theory of the 

 hardening of steel by quenching, published by him in 1805, and recently 

 revived by Grenet, in which the effects were ascribed to deformation 

 (ecrouissage) of the metal. The change in volume accompanying the 

 transformation of steel on cooling, causes internal stresses of great 

 magnitude when the metal is quenched from a temperature above the 

 change point. The author considers that the deformation caused by 

 these stresses hardens the steel, while Grenet's view is that the hardness 

 is due to a change of texture. Arguments tending to show that the 

 two views are in essential agreement, are advanced. 



Cementation. § — Ledebur combats the theory of cementation of steel 

 advanced by Guillet, and takes the view that the solid carbon is directly 



* R6v. Metallurgie, iii. (1906) pp. 105-6. 



t Tom. cit., pp. 155-79 (28 figs.). 1 Tom. cit., pp. 211-16. 



§ Tom. cit., pp. 222-6. 



