ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 519 



are given showing that anneaUng causes coalescence of the cuprous 

 oxide globules in the eutectic with consequent diminution of the 

 crystalline continuity of the latter. It is suggested that this structural 

 change partly accounts for the improvement in conductivity of annealed 

 wire over that of the cast copper. 



Heat Treatment of Aluminium-bronze."' — The structures of an 

 aluminium-bronze containing ID p.c. aluminium, after quenching at 

 various temperatures from 500° to 900° C, and also after annealing at 

 various temperatures following quenching at 800° and 900°, are described 

 by A. Portevin and G. Arnou, and illustrated by several photomicro- 

 graphs. The changes in structure are such as would be anticipated for 

 an alloy of this composition from the equilibrium diagram, showing an 

 eutectoid change at 550° C. The annealed alloy consists of crystals of 

 the a solid solution and a dark etching eutectoid (a-i-y). Quenching 

 at 500° produces no modification of structure ; quenching at temperatures 

 above 550° gives rise to the appearance of a martensitic constituent ; and 

 after quenching at 900° the structure is completely martensitic, in which 

 the grain-boundaries of the ^ constituent stable at high temperatures are 

 clearly marked. Subsequent annealing causes further separation of the 

 a phase, the needles become more numerous and tend to thicken and 

 become rounded. For etching the specimens an alcoholic solution of 

 ferric-chloride was employed. The strength, ductility, hardness, and 

 shock-resisting values of the alloy after each treatment are also given. 

 With the appearance of the martensitic constituent there is an increase 

 in strength and hardness, and within limits an increase also in ductility 

 and resistance to shock. 



Case-hardening of Iron by Boron. j— In view of the remarkable 

 hardness of iron-boron alloys the case-hardening of iron by boron, 

 similarly to the case-hardening of iron by carbon, is suggested by N. 

 Tschischewsky. In preliminary experiments — heating in vacuo for two 

 hours at 950° C. with a finely powdered ferro-boron alloy (19 p.c. boron) 

 as case-hardening material — the boron penetrated a low carbon steel to 

 a depth of one millimetre. Microscopic examination showed that the 

 hard white layer of the case-hardened part consists of compact boric- 

 pearlite. The inner part of the lajer contains the boron in solution in 

 the ferrite. The cementation was not so rapidly effected when pure 

 amorphous boron was employed as the case-hardening material. 



Carbon- Concentration and Exfoliation in the Case-hardening of 

 Steel. J — E. P. Stenger describes experiments upon the cementation of 

 steel in which four steels of the types usually employed for industrial 

 cementation were heated in the form of thin disks at constant tempera- 

 ture in a carbonizing material, with the object of finding the maximum 

 concentration of carbon in the steels corresponding to each temperature. 

 The temperatures varied from 730° to 1140° C. Microscopical examina- 

 tion of transverse sections of the disks after cementation showed a 



* Rev. Metallurgie, xiii. (1916) No. 2, pp. 101-15 (15 figs.). 



t Jouru. Iron and Steel lust., xcv. (1917, 1) pp. 185-7 (2 figs.). 



X Met. and Chem. Engineering, xvi. (1917) No. 8, pp. 425-33 (26 figs.). 



