ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 4 - J7 



vection currents. It is probable that surface tension plays a part in 

 determining the external form of metallic crystallites. The programme 

 of experimental work proposed includes the microscopic examination 

 during crystallization, of small masses of metals of low melting point, 

 melted on an electrically heated Microscope stage, and covered by a 

 thin cover-glass of transparent silica. The numerous references given 

 form a useful bibliography. 



Processes of Solidification and Grain Growth in Metals.* — F. 

 Robin discusses the crystallization of metals from the liquid state and 

 the phenomena observed during solidification and during the growth of 

 metal crystals in the solid state. The results of a considerable volume 

 of experimental work are reported. The observations of hot metals 

 were made through the long-focus binocular stereoscopic Microscope 

 previously described by the author. In a pure metal the solid surface, 

 immediately after solidification, is smooth like the liquid surface, while 

 crystallites may form in less pure metals. Then two systems of lines 

 forming networks appear: (1) the crystal boundaries; (2) Cartaud's 

 cellular network. AH these lines are below the general level of the 

 surface. On remelting, the network of crystal boundaries is the first to 

 melt, and the level of the lines rises to that of the surrounding surface. 

 The possibility of amorphous solidification followed by crystallization is 

 suggested. Experiments on tin and lead have indicated that when a 

 metal solidifies undisturbed by external mechanical influences the result- 

 ing structure is very stable and persists unchanged during reheating 

 until the metal melts. Cartaud's cellular network is regarded as a con- 

 traction effect caused by a general shrinkage of the metal at the instant 

 at which solidification is complete. Surface tension is an important 

 factor in the growth of crystals on annealing. 



Metallog-raphic Laboratory. f — H. Hanemann states briefly the 

 necessary requirements in the outfit of a metallographic laboratory. 



* Rev. Metallurgie, xi. (1914) pp. 489-512 (21 figs.). 

 t Stab! und Eifen, xxxiv. (1914) p. 153. 



