ZOOLOGY AND BOTANY, MICROSCOPY, ETC. BIS 



(61 Miscellaneous. 



Cleaning used Microscope Slides.* — J. T. lUick gives the following 

 method : A liberal ainount of gold dust and a number of slides were 

 placed in water and thoroughly boiled. As soon as the cover-slips 

 came off of their own accord the slides and slips were placed in a pan of 

 water. These were wiped dry while others were being boiled. 



Metallography, etc. 



Alumina in Steel. f — The question of the occurrence of alumina 

 inclusions in steel and their detection by the Microscope has been 

 studied by A. Sauveur, by (1) producing thermite iron with an excess of 

 ahiminium ; (2) melting ingot iron with aluminium ; (3) melting ingot 

 iron with alumina. In each case polished but unetched sections of the 

 metal exhibited under the Microscope, at a magnification of 300 diameters, 

 small, dark and roughly rounded particles scattered throughout the iron. 

 Characteristics of alumina inclusions, by which they may be distinguished 

 from other non-metallic inclusions generally occurring in steel, are their 

 dark colour, small size and complete absence of any elongation in the 

 direction of rolling or forging. This agrees with the known brittleness 

 and infusibility of alumina. 



Study of Cooling- Rates with a Chromium Steel. | — C. A. Edwards 

 heated cubes of a steel containing 0'G3 p,c. carbon and 6 "15 p.c. 

 chromium to 1147° C, and cooled at varying rates. A critical rate of 

 cooling was found — namely, twelve minutes sixteen seconds — from 836^ C. 

 to 546° C. For all slower rates of cooling, recalescence occurred during 

 the cooling, and the hardness produced was very similar. When the 

 rate of cooling is quicker than the critical rate, the thermal change is 

 much modified, or, with very quick cooling rates, repressed altogether, 

 and the steel is progressively hardened, according to the quickness of 

 the cooling. The critical cooling-rate varies with the initial tempera- 

 ture of cooling. The higher the initial temperature, the slower is the 

 critical rate of cooling. Photomicrographs of structures of the steel 

 corresponding to different rates of cooling are given. Samples cooled at 

 rates slower than the critical rate, and therefore not self-hardened to any 

 appreciable extent, consisted generally of troostitic pearlite, with very 

 little martensite. Samples cooled quicker than the critical rate contained 

 large quantities of martensite, which is responsible for the self-hardening. 

 When the cooling was sufficiently rapid to suppress altogether the thermal 

 change and produce maximum hardness, the structure was all martensitic. 



Corrosion of Steel.§ — L. Aitchison discusses the mechanism of 

 corrosion in pure iron and the various kinds of steel. In steels 



* Trans. Amer. Micr. Soc, xxxv. (1916) p. 141. 

 t Metall. and Chem. Engineering, xv. (1916) pp. 149-51 (4 figs.). 

 X Journ. Iron and Steel Institute, xciii. (1916) pp. 114-40 (8 figs.). 

 § Journ. Iron and Steel Institute, xciii. (1916) pp. 77-91 (6 figs.). 



