Zom|,(k;v ANI» BOTANY. MICROSCOPY, ETC. 6G9 



crucible containing the metal the boiling-point of which was to be de- 

 termined. The temperature of the outer walls of the crucible was taken 

 by a Wanner optical pyrometer. The surface of the metal was observed 

 from above ; the commencement of boiling could easily be noted. For 

 metals which combine with carbon, the graphite crucibles were lined with 

 magnesia. The following temperatures are given as approximate boiling- 

 points : — 



Aluminium 1800° C. Copper .. 2310° C. Manganese 1900° C. 



Antimony 1440 Iron .. 2450 Silver .. 1955 



Bismuth.. 1420 Lead ., 1525 Tin .. 2270 



Chromium 2200 Magnesium 1120 



Structure of Steels at High Temperatures.* - - A. Baykoff first 

 continued Maurer's results by obtaining homogeneous austenite from a 

 steel containing 1*79 p.c. carbon, 2 '14 p.c. manganese, - 89 p.c. 

 silicon, quenched from 1110 C. Pure austenite has been defined by 

 H. le Chatelier as a solution of carl ion in y-iron, stable between the 

 solidification temperature and a temperature varying from 700-1200° C 4 , 

 according to carbon content. The purest austenite hitherto obtained, 

 homogeneous at ordinary temperatures, is Maurer's, containing about 

 2 p.c. manganese. In order to ascertain the structure of pure austenite 

 in its stable range, the author etched previously polished sections of 

 five steels containing 0*12-1*94 p.c. carbon, some being almost free 

 from other elements, at 1120° C. The polished sections were placed 

 in the porcelain tube of an electric resistance furnace. Hydrogen was 

 passed through for several hours, and the temperature was then raised 

 to the required degree. Hydrochloric acid was then introduced for 

 several seconds, the current of hydrogen continued for 2 to :! hours, 

 and the furnace allowed to cool. The steels, etched in this way at 

 1120° C, all showed the polyhedric structure characteristic of austenite. 

 Twinning was noted in several cases. Etching at 870° G. in a similar 

 way failed to reveal a martensite structure. Martensite does not appear 

 to be stable at any temperature, but to be a structure developed only by 

 quenching. 



Structure of Hardened Steel. f--W. J. Kurbatow and M. M. 

 Matwejew find that the best method of producing austenite is to quench 

 steel of 1*8-2 2 p.c carbon, heated nearly to melting, in mercury at 

 130° C. The lance-shaped crystals occurring between the austenite 

 crystals, are troosto-sorbite. The equilibrium austenite TJ!; sorbite 

 proceeds from right to left between 90° and 150° C, and above 1000° C. 

 Between 150° and 750° C. the equilibrium proceeds from left to right, 

 most rapidly at 250° C. All the constituents of steel are crystalline. 

 Austenite is probably a carbide of iron Fe 7 C (?) (Fe 6 C -- Fe 10 C). 

 Troostite and sorbite are solutions of carbon in iron, a or (3. The 

 austenite is unchanged after heating at 65—85° C. for several months. 

 At 118° 0. recrystallisation is evident in a few days. At 180° C. 

 austenite changes to troostite. The old scheme of transformation 

 austenite-martensite-troostite-sorbite-pearlite is inaccurate. 



* Rev. de Metallurgie, vi. (1909) pp. 829-34 (10 figs.), 

 t Metallurgie, v. (1908) pp. 721-8 (8 figs.). 



