438 SUMMARY OF CURRENT RESEARCHES. 



phases may cause the external surface to differ considerably from a 

 section. Further, in order that structure may be satisfactorily revealed 

 by etching, it is necessary that the structure should not change appreci- 

 ably during etching. But the growth of crystals at high temperatures 

 in some materials, e.g. high-carbon steel at 1000° C, is so rapid that 

 the structure may alter considerably even in the short time required 

 for etching. 



Thermal Investigations in a Vacuum.* — W. Heike describes a 

 new method of preparing and thermally investigating alloys. Weighed 

 quantities of the metals are placed in a porcelain tube, which is then 

 evacuated and sealed up. The tube is heated above the melting points 

 of the elements, suitably shaken and allowed to cool. Specimens pre- 

 pared in this way are very suitable for microscopic examination. The 

 rough surface of the metallic regulus often affords valuable information 

 upon the crystalline habit of the alloy. Examples taken from the 

 copper-silver series are described and illustrated. 



* Int. Zeitscbr. Metallographie, iv. (1913) pp. 143-54 (11 figs.). 



