ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 389 



published coefficients of expansion. An alloy of components completely 

 insoluble in each other in the solid state contracts less than either 

 of its components ; the eutectic alloy having the smallest shrinkage- 

 coefficient. An alloy consisting of one or more solid solutions contracts 

 more than either of its components. Neither in metals nor alloys 

 could a definite relationship between shrinkage and melting point be 

 discerned. 



Metastability of Metals.* — E. Cohen and K. Inouye find that other 

 metals exhibit phenomena resembling those observed in connection with 

 the '• strain-disease " of tin. Pieces of hard-rolled thin sheet of the 

 metals (lead, copper, zinc, nickel, bismuth, brass) were etched with some 

 figure, such as a cross, placed in contact with similar but unetched 

 pieces between two iron plates, and heated for a number of hours at 

 constant temperatures, for instance, 100° C. or 180° C. In many cases 

 the unetched strip was " infected," and showed a figure similar to that 

 etched on the piece with which it was in contact. The inoculation did 

 not occur in the cold. From these and other observations the authors 

 infer that the common metals, as usually employed in a mechanically 

 strained condition, are metastable, and may pass into a more stable form 

 through inoculation as well as by heating. 



Crystalline Structure of Iron at High Temperatures, f — W. 

 Rosenhain and J. C. W. Humfrey have made some preliminary experi- 

 ments on the microscopical effects of strain in iron at high temperatures. 

 A polished strip of sheet iron was heated in a high vacuum ; it was 

 held in such a manner that the release of a strong spiral spring, by 

 electrical means, caused a pull on the specimen sufficient to deform it. 

 The iron strip was strained when the temperature at its centre exceeded 

 1000° C, the ends not being visibly red. When cold, the specimen 

 was examined microscopically. In a similarly heated but unstrained 

 specimen, three regions of different appearance were noted. At the 

 ends the surface was unchanged. Where the temperature approached 

 redness, a system of interlacing black lines was seen, and in the central 

 (hottest) part, a faint tinting, apparently caused by slight oxidation, 

 revealed a new crystallisation, of coarser and more regular structure, 

 characterised by numerous examples of twinning. Upon these appear- 

 ances were superposed, in the strained specimen, the effects of deformation. 

 While the area of medium temperature, characterised by the interlacing 

 black lines, showed no signs of plastic deformation, the neighbouring 

 regions, both cooler and hotter, showed slip-bands and other clearly 

 marked strain effects. The authors identify the three regions with the 

 a, (B, and y forms of iron, and consider that the absence of strain effects 

 in the region corresponding to the /? form, indicates the greater hard- 

 ness of this allotropic modification. The interlacing black lines noted 

 in this region are held to be caused by a volume change occurring when 

 a changes to /3 and ft to a, this volume change producing relative move- 

 ment of the crystals. An approximate measurement of the temperature 

 of different points in a heated and strained specimen was made by 



* Zeitschr. Phys. Chem., Ixxi. (1910) pp. 301-11 (3 figs.), 

 f Proc. Key. Soc, Series A,lxxxiii. (1910) pp. 200-9 (5 figs.). 



