ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 113 



questions were dealt with in an elementary manner. The formation of 

 a eutectic network by the addition of a small percentage of bismuth to 

 gold, the electrolytic decay of brass resulting in dezincification, the 

 structure of steel, and the failure of steel by fatigue, were among the 

 subjects touched upon by the lecturer. 



Crystallisation of Minerals.* — T. M. Lowry discusses Day and 

 Shepherd's study of the crystallisation of the lime-sihca series. Among 

 the many difficulties which surround the determination of melting points 

 of minerals are the excessively high temperatures and the slowness with 

 which many minerals attain equilibrium on change of temperature. The 

 employment of the radiation pyrometer, and of iridium vessels (melting 

 point at least 600° C. above that of platinum), has rendered possible 

 accurate work at very high temperatures. The equilibrium diagram 

 given indicates the formation of two definite compounds (CaSiOg and 

 CaoSiO^) and three eutectics. Silica, and the two compounds, are 

 polymorphous. 



Practical Applications of Microscopic Metallography in Works.f 

 In this paper, read at the Brussels Congress of the International Associa- 

 tion for Testing Materials, H. le Chatelier gives a comprehensive and 

 somewhat lengthy review of the subject. The paper is divided into 

 sections as follows : (1) Examples of practical application — three striking- 

 instances are given. (2) Information furnished by microscopic examina- 

 tion, bearing on («) chemical composition, (b) structure, (c) deformations. 

 (3) Ways in which metallography may be employed in works, (a) for the 

 regular control of manufacturing operations, {b) for research with a 

 particular object in view, (c) for research of a more indirect and general 

 nature. (4) Particular industries in which metallography is of value. 

 (5) Cost of metallography. Numerous examples are given, fully illus- 

 trated by photo-micrographs. 



Quenching of Steel. | — P. Lejeune describes a method of studying 

 the rate of cooling of large pieces of steel in quenching. The Saladin 

 method of recording differences of temperature is used. Two thermo- 

 couples are inserted in the sample (a cylinder 5 cm. by 5 cm.), the junc- 

 tion of one being at the centre, that of the other midway between centre 

 and surface. By means of suitable connections of these couples to 

 galvanometers, the actual temperature of the centre, and the difference 

 of temperature between the two points are recorded. A resistance 

 furnace with carbon as the resistor was used for heating the samples. 

 The author gives some curves he has obtained. 



Some Obscure Points in the Theory of Cementation.§ — Partiot 

 indicates the wide range of application of case-hardening, and suggests 

 that researches on the following lines will give results of practical value : 

 (1) Determination of the laws giving the depth of penetration as a 

 function of time and temperature ; (2) study of cementing media and 

 " anti-cements " (substances which prevent or retard cementation) ; (3) 



* Nature, Ixxv. (1906), pp. 112-3 (1 fig.). See also Journ. Amer. Chem. 

 Soc, xxviii. (1906) pp. 1089-1114. 



t Rev. M6tallurgie, iii. (1906) pp. 493-517 (86 figs.). 



t Tom. cit., pp. 528-34 (8 figs.). § Tom. oit., pp. 535-40. 



Feb. 20th, 1907 I 



