ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 039 



S(;opical examination of leatlier. In a note the autlior mentions th;it 

 Becker ascribed these spots to the action of micro-organisms, bnt with 

 tliis view he does not agree. He divides the spots into two groups, 

 the first of which is characterized by the presence of calcium phospliate, 

 derived from the sulphate, while in the second grouj) there is no 

 accumulation of this salt. He concludes by saying that the determining 

 cause of the spots is special for each group, grains of calcium sulphate 

 in the first case, and in the second possibly the presence of bicarbonate 

 of iron due to microbic action. It is remarkable, however, to find that 

 the spots in the latter instance show less degeneration tlian in the 

 former class ; hence it may be inferred that microbic action could not 

 have been very severe. 



The article is very interesting throughout, and is a good example 

 of the utility of the Microscope and microscopical methods in the Arts 

 and Crafts. The coloured illustrations in the plates are extremely good. 



Metallography, etc. 



Structure of Steel.* — S Y. Bielynsky oliserves that in one and 

 the same specimen of steel three classes of structure, dendritic, reticular, 

 and granular, may be detected by examination with the naked eye or 

 with a low power. Steels of different carbon content, cooled from the 

 liquid state rapidly,, slowly, or at an intermediate speed, were prepared. 

 Sections were polished and submitted to the action of neutral 1 p.c. 

 copper sulphate solution in water. Examination was made before and 

 after the removal of the thin layer of copper by washing, and also 

 after a further rubbing on 000 emery paper. The reticular structure 

 is formed by the ferrite and cementite, the granular structure by small 

 surfaces reflecting light at slightly different angles, the specimen some- 

 what resembling a galvanized iron surface. An elaborate system of 

 classification of steels, based on the various combinations and relation- 

 ships of the three classes of macrostructure, is given. 



Quenching of Hypereutectoid Tool Steels.* — S. S. Steinberg has 

 examined broken tools which showed a coarse fracture. The micro- 

 structure indicated that the coarse fracture was not due to overheating 

 before quenching ; the cementite was in the form of a network and 

 needles, the mass of the steel being martensite and troostite. The 

 brittle cementite network appeared to be the cause of the coarse 

 fracture. Forging at 900" C. followed by quenching at 800° 0. gave 

 a fine fracture, but the same result was more readily obtained by 

 quenching from 900-950° 0., reheating to 800° C, and quenching 

 again. The cementite then took the form of small particles disseminated 

 throughout the steel. Heating to 900-950° C. is necessary to dissolve 



* Rev. 3oc. Russ. Met., 1912, pp. 396-420, through Rev. M^tallurgie, x. (1913) 

 extraits, pp. 495-502 (4 figs.). 



t Rev. Soc. Russ. Met., 1912, pp. 613-15, through Rev. M6tallurgie, x. (1913) 

 extraits, p. 502. 



