ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 321 



So-called " Crystallization through Fatigue."*— F. Rogers has 

 failed to find any experimental evidence in support of the prevalent 

 idea that fatigue may cause a development of crystallization in iron or 

 steel. It is probable that the only alterations in structure which repeated 

 stress is capable of causing are destructive. Strain effects may be 

 classified as (1) slip-bands ; (2) intergranular weakness ; (3) twinning, 

 and the formation of Neumann lamellae ; (4) change of structure. Of 

 these the first is the commonest and is almost universal. The examina- 

 tion of numerous samples has led to the conclusion that if a piece 

 breaks in service with a crystalline-looking fracture, it would also have 

 done so when new. Pieces which had broken in use, giving fractures 

 partly crystalline and partly fibrous, were found to be heterogeneous in 

 structure, the different types of fracture corresponding to different 

 structures. 



Preparing Sections of Fractures of Steel for Microscopic Exami- 

 nation.f — For the examination of a section through a fracture, A. 

 Campion and J. M. Ferguson recommend the embedding of the fracture 

 in a fusible alloy, in cases where time is not available for the lengthy 

 process of electro-deposition of copper or iron. Suitable alloys are : — 



A B 



Bismuth 50 parts 50 parts 



Lead 30 „ 30 „ 



Tin 25 „ 10 „ 



Zinc 3 „ 



Cadmium 10 ,, 



Both alloys melt below 100° C. A is the better alloy, but has a 

 melting-point 25° C. above that of B. If a section through a fractured 

 test-piece is required, the fracture is momentarily dipped in hydrochloric 

 acid of 1 • 1 sp. gr., then in zinc-chloride solution, aud is then plunged 

 into a quantity of the molten alloy in a suitable mould. The alloy is 

 re-warmed to ensure fluidity and to allow trapped air to escape. The 

 embedded specimen, when cold, may be sawn in any required direction 

 and polished by the usual methods. 



Transparence or Translucence of the Surface Film Produced in 

 Polishing Metals. $ — If a specimen of copper containing blow-holes is 

 polished, the smaller pits in the surface become covered over by the 

 surface skin formed by polishing. G. T. Beilby shows that the film 

 which covers the pits is transparent, or at any rate highly translucent, 

 and that the mobile film has been carried across the empty pit without any 

 support from below, such as might have been given by particles filling 

 up the pit. By carefully regulated etching of the surface with a reagent 

 which dissolves copper, the film can be reduced to extreme thinness and 

 finally dissolved completely, exposing the open pit. In the polished 

 surface, under high magnification, the pits appear as blue spots on a 

 rose-coloured ground. Some of the blue spots showed patches of red. 

 By dissolving away the film the patches of red were shown to be due to 



* Journ. Iron and Steel Inst., lxxxviii. (1913, 2) pp. 392-8 (2 figs.). 

 + Journ. Iron and Steel Inst., lxxxviii. (1913, 2) pp. 385-91 (5 figs.). 

 X Proc. Roy. Soc, Series A, lxxxix. (1914) pp. 593-5 (4 figs.). 



