ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 343 



other, and making it possible to follow the distribution of the distortion 

 produced by forging or rolling. 



Micro-Chemical Examination of Lead- Antimony Alloys. * -J. E. 

 Stead has made a laborious investigation of these compounds. He finds 

 that the eutectic alloy has a percentage composition of 12*8 of antimony 

 and 87-2 of lead, corresponding nearly with the formula Pb 4 Sb. Its 

 fusible point was 247° C, and specific gravity 10*48. Microscopicay 

 examination of the eutectic showed a structure similar to that of 

 other well-investigated alloys. At fairly equable distances apart, what 

 appeared to be laminae radiated from nuclei and continued in right lines 

 until met by similar radiations from other nuclei. The appearance is 

 similar to that of nodules of pyrites with radial structure or spherulites 

 in obsidian. Further examination showed that these laminas split up 

 into excessively fine rod-like bodies, which, but for their absolute 

 opacity, might be mistaken for certain forms of bacteria. It appears 

 certain then that the eutectic alloy is composed of alternate laminae oi 

 lead and antimony, each lamina being itself composed of crystals. In 

 spite of the composition Pb 4 S, there does not appear to be chemical 

 union between the lead and the antimony. 



Study of White Alloys called Antifriction.f— M. Charpy, after an 

 exhaustive investigation, concludes that all the alloys used for anti- 

 frictional purposes possess the same general characteristics ; they are 

 composed of hard grains imbedded in a plastic alloy. This constitution 

 fulfils the two requirements of bearing alloys ■ the load is carried by 

 the hard grains which have a low coefficient of friction, and the 

 *' cutting" (grippemeni) of which can take place only with great diffi- 

 culty ; the plasticity of the cement makes it possible for the bearing 

 to adjust itself closely round the shaft, thus avoiding local pressures 

 which are the principal cause of accidents. Such coustitution may be 

 produced in binary alloys, the hard grains being made up by a single 

 metal such as antimony, or by a definite compound such as antimonide 

 of zinc. It is generally preferable, however, to use ternary mixtures, 

 because, owing to the complex composition of the cement, the constitution 

 possessing the required qualities may be more readily obtained. 



Microstructure of Cementation. J — Professor J. 0. Arnold, after 

 a thorough micrographic study of cemented iron bars, arrives at the 

 following provisional conclusions: — (1) That the diffusion of carbon 

 in the process of cementation presents two distinct varieties of " inter- 

 penetration": (a) The interpenetration of the substance corresponding 

 with the formula Fe 24 C and pure iron ; (b) the interpenetration of the 

 normal carbide Fe 3 C and the sub-carbide Fe 24 C. (2) That the inter- 

 penetration of Fe 24 C and iron is more rapid, and takes place at a lower 

 temperature than the interpenetration of Fe 24 C and Fe 3 C. (3) (a) That 

 the interpenetration of Fe 24 C and Fe begins" at Ar 2 (about 750° C), and 

 is coincident with the evolution in vacuo of gases from the iron : 

 (6) that the interpenetration of Fe 24 C and Fe 3 C does not take place- 

 till a temperature of about 950° C. has been reached. 



* Metallographist, i. (1899) pp. 179-92 (2 figs). 



t Tom. cit., pp. 9-55 (29 figs.). % Tom. cit., pp. 5G-G9 (11 figs.). 



2 A 2 



