194 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Metallography, etc. 



Polymorphism of Zinc* — G. \. Petrenko states that the polished 

 surface of zinc cooled slowly from above its melting-point to 180° C. 

 exhibited large polyhedra upon which comparatively few small ones 

 were disposed promiscuously ; the small polyhedra were mure abundant 

 when the metal was quenched at 300-830° C, but completely covered 

 the surfaces of the large crystals when the metal was cooled to just 

 below 30o c C. The phenomenon was reversible, and is considered to 

 indicate the occurrence of an allotropic transformation between 290° 

 and 300° C. 



Tensile Properties of Copper at High Temperatures,! — G. D. 

 Bengough and D. Hanson have made tensile tests on copper at tem- 

 peratures up to 1000° C, in oxidising, neutral, and reducing atmospheres, 

 and have recorded the microstructure of the broken specimens. In 

 order to preserve the actual edge of the fractures during polishing, the 

 specimens were electroplated with a thin coating of nickel, on w r hich a 

 thick coating of copper was deposited, and were then cut through at the 

 desired position and polished in the usual way. Satisfactory etching 

 was obtained, with some difficulty, by using a lo p.c. solution of 

 ammonium persulphate containing excess of ammonia. In pure copper 

 two types of fracture are distinguished, the low-temperature type which 

 passes through the crystals, and the high-temperature type, observed in 

 specimens broken at temperatures between 720° C. and the melting- 

 point, which is intercrystalline. In the high-temperature intercrystalline 

 fracture there is no distortion of the crystals. The results are considered 

 to support the hypothesis of the existence in pure metals of an inter- 

 crystalline cement, highly elastic at relatively low temperatures, which 

 loses its strength with rise of temperature much more rapidly than do 

 the crystals themselves. 



Annealing of Brass. J — Commercial castings of the alloy copper 70, 

 zinc 29, tin 1 p.c, contain a complex eutectoid, in which the light- 

 coloured brittle tin-rich constituent appears to be the 8-phase of the 

 copper-tin system. On heating, this eutectoid is transformed to 

 homogeneous (3 at about 600° C., and at higher temperatures the (3 

 diffuses into the a solid solution. F. Johnson has examined a 7<t-2',)-l 

 tube-casting which cracked badly during the drawing process. The 

 casting contained intercrystalline eutectoid, through which the cracks 

 frequently ran. The presence of the brittle eutectoid, the cause of the 

 cracking, indicated that the casting had not been sufficiently annealed. 



* Journ. Russ. Phys. Chem. Soc, xlvi. (1914) pp. 176-78, through Journ. Soc. 

 Chem. Ind., xxxiii. (1914) p. 1212. 



t Journ. Inst. Metals, xii. (1914, 2) pp. 56-88 (21 figs.). 

 X Journ Inst. Metals, xii. (1914, 2) pp. 111-15 (9 rigs.). 



