ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 319 



forms of heat-treatment. No marked change in crystallization oc- 

 curred at temperatures below 900° C. Re-crystallization occurred at 

 910° to 915° C, and was complete after two or three seconds in that 

 temperature zone. Specimens heated above 910° C. had a fine structure 

 if queuched in water, but when any slower rate of cooling was adopted 

 the crystals formed were relatively enormous, the resulting structure 

 being very much coarser than that of the original strip. The first new 

 crystals were equiaxed, but specimens which had been heated to 930° C. 

 contained radial crystals, which increased at the expense of the equiaxed 

 crystals with higher temperatures of treatment. 



By quenching at different temperatures on cooling from above Ac 3 , 

 the temperature of recrystallization, it was shown that the large crystals 

 were formed during the passage through Ar 3 . Coarse crystals did not 

 develop with any rate of cooling after a very prolonged heating above 

 Ac 3 . The large crystals, once formed, could only be destroyed by 

 mechanical work, or by quenching from above Ac 3 , or by prolonged 

 heating above Ac 3 . The formation of the excessively large crystals 

 described did not occur in electro-deposited iron if the thickness of the 

 strip exceeded a critical value lying between O'Oll and - 012 inch, and 

 did not occur at all in wrought-iron or mild steel. It is suggested that 

 the formation of the coarse crystals may be promoted by the persistence 

 of nuclei of crystallization when heating above Ac 3 is not prolonged, but 

 that long-continued heating above Ac 3 destroys these crystal nuclei. 



Belaiew's Researches on the Structure of Steel.* — N. T. Belaiew's 

 account of his studies upon the structure of steel was published in book 

 form in the Russian language. W. Guertler now gives a summary, 

 illustrated with 22 photomicrographs, and points out the general 

 significance of the observations recorded and their parallels in other 

 series of alloys. The structures described are chiefly those of specimens 

 heated for long periods at high temperatures and very slowly cooled. 



Structural Changes of Iron during Annealing. f — D. Ewen has 

 studied the heat-reliefs formed on polished specimens of pure Swedish 

 iron on heating to temperatures of 400° to 1000° C. in a high vacuum. 

 Three distinct types of heat-relief, corresponding to (1) initial a- and 

 /3-iron structure, (2) y-iron structure, and (3) final (3- and a-iron struc- 

 ture, are described. The development of the a-iron heat-relief on 

 heating is ascribed to selective volatilization from the crystal boundaries, 

 while the y-iron and final (3- and a-iron heat-reliefs obtained on cooling 

 are attributed to differences in dilatation of the allotropic modifications 

 involved. An etching effect, frequently giving rise to definitely oriented 

 pits, was obtained above A 3 , more especially when the metal was heated 

 by passing a heavy current through it, and is ascribed to a species of 

 electrical disintegration. 



"&' 



Damascene Steel. $ — W. Guertler criticizes the various methods that 

 have been proposed for preparing damascene steel. True damascene; 



* Int. Zeitschr. Metallographie, vi. (1914) pp. 72-89 (23 figs.), 

 t Int. Zeitschr. Metallographie, vi. (1914) pp. 1-17 (10 figs.). 

 I Int. Zeitschr. Metallographie, v. (1914) pp. 129-41 (9 figs.). 



