ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 197 



favoured the formation of a dendritic structure, and more rapid cooling 

 produced a granular structure. In rolled material such as plates, the 

 sulphide and silicate of manganese are often present in fine broken 

 threads, as well as in the usual ellipsoidal form. The author suggests 

 that the threads were originally cellular films in the ingot, while the 

 ellipsoidal masses were globules. 



Slag Inclusions in Steel.* — F. Giolitti and S. Zublena give the 

 results of heat- treatment experiments on an acid open-hearth steel con- 

 taining 0*38 p.c. carbon, and 2 p.c. nickel, intended to ascertain the 

 effect of the slag inclusions present. The extent to which separation of 

 ferrite round the inclusions occurred was influenced by the conditions of 

 heating, whether carburizing or decarburizing. By appropriate heat- 

 treatment, the injurious effects of slag inclusions may be diminished or 

 even eliminated. 



Annealing of Tyres.f — A. L. Babochine points out that the desirable 

 structure in a steel tyre is a fine-grained sorbitic structure, and indicates 

 the theoretical conditions for the production of such a structure by 

 annealing. The tyre should be heated above A3 for a length of time 

 sufficient to destroy the original structure, and to produce a uniform solid 

 solution. Cooling to a temperature below Al should be moderately 

 rapid, and the subsequent cooling slow. In practice the annealing tem- 

 perature should not be below 800 o -840 o C. The microstructures of tyres 

 correctly annealed, and of tyres the annealing of which had been faulty 

 in different ways, are illustrated by photomicrographs. Common faults 

 in structure are coarsely lamellar pearlite, granular pearlite, and a coarse 

 cellular structure. 



Microscopical Investigation of Opaque Minerals.! — 0. Stutzer 

 discusses the application in petrography of the microscopical examination 

 of minerals by means of reflected light. Chalcopyrite, iron pyrites, 

 pyrrhotite, and other coloured minerals can be detected in a polished 

 section of the ore, while etching may be required to distinguish between 

 minerals of similar colour. In nickelif erous pyrrhotite, the nickel is seen 

 to be associated mechanically with the pyrrhotite in the form of pentlan- 

 dite, whereas formerly it was considered to be in chemical combination 

 in the pyrrhotite. In titan if erous magnetite the titanium occurs partly 

 in mechanical association with the magnetite as ilmenite, and in part 

 replaces the iron chemically in the magnetite molecules. Such specimens 

 of titaniferous magnetite may be etched with hydrochloric acid, which 

 dissolves the magnetite and leaves the ilmenite unaffected. In copper- 

 iron pyrites, bornite 3 Cu 2 S, Fe 2 S 3 , copper glance Cu 2 S, chalcopyrite 

 CiiFeS 2 , enargite Cu 3 AsS 4 , and iron pyrites FeS 2 may all be identified by 

 their microscopical characteristics. 



* Annali Chim. Appl. ii. (1914) pp. 218-245, through Journ. Soc. Chem. Iud., 

 xxxiii. (1914) p. 1210. 



t Rev. Soc. Russ. Met., i. (1913) pp. 387-705, through Rev. Metallurgie, xi. 

 (1914), Extraits, pp. 594-599 (9 figs.). 



X Metall. und Erz., xi. (1914) pp. 450-455, through Journ. Soc. Chem. Iud., 

 xxxiii. (1914) p. 1160. 



