ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 501 



Ternary Systems.* — E. Janecke discusses the constitution of various 

 types of ternary systems, classifying them according to the constitution 

 of the binary systems of which they may be considered to be composed. 

 As examples of the different types, systems are selected containing three 

 of the following metals : copper, silver, gold, chromium, manganese, iron, 

 cobalt, nickel, palladium, platinum. 



Pseudo-binary Alloys. f — If in a metallic binary system the two 

 components A B form a compound C, it is usually assumed that the 

 complete equilibrium-diagram may be regarded as being composed of the 

 diagrams of the systems AC and C B, merely juxtaposed. This involves 

 the assumption that A and B cannot co-exist in equilibrium, one or the 

 other of the two metals being completely combined in the compound C. 



A. Portevin draws attention to the possibility of a partial dissociation of 

 the compound resulting in the co-existence of A, B, and C. In such a 

 case the system must be regarded as ternary, the components being A, 



B, and C. The theory of equilibrium of such systems is worked out at 

 some length, on the lines indicated by Roozeboom and Aten. Among 

 the systems to which the theory is applied are aluminium-antimony, 

 iron-molybdenum, and iron-chromium. 



Apparatus for Microscopical Examination of Metals.} — A. Sauveur 

 describes the appliances he has found most satisfactory. Specimens of 

 steel and other magnetic substances may be held on the microscope stage 

 by a magnetic holder. This device is a thin V-shaped permanent magnet, 

 1 inch wide, 2h inches long. It is placed on the Microscope stage like a 

 glass slip, the specimen is held magnetically with its polished surface 

 against the lower surface of the holder. Small sections are suspended 

 near the small end of the Y-opening, large ones being placed near the 

 wider end. The plain glass illuminator is preferred to the prism type. 

 A simple form of inverted Microscope with horizontal photomicrographic 

 camera is described, though for photomicrography a vertical Microscope 

 and camera are recommended. The stand, objectives, eye-pieces, illumi- 

 nators, sources of light, condensers, and cameras, are all of well-known 

 types. 



Colour-etching of Steel. § — F. Robin and P. Gartner recommend the 

 following method of etching for austenitic and martensitic steels. The 

 polished surface is immersed in a saturated solution of picric acid in 

 alcohol for 30 to 60 seconds, is then washed in water and allowed to dry 

 slowly in air. From the colours observed on a surface etched in this 

 manner much information as to the nature of the austenite or martensite 

 may be obtained. Differences in speed of etching also serve to distinguish 

 different natures of steel. The authors describe in detail the micro- 

 scopical characteristics of a number of steels of different compositions 

 treated to give austenite or martensite in large quantity. 



* Metallurgie, vii. (1910) pp. 510-23 (46 figs.). 



t Rev. Metallurgie, viii. (1911) pp. 7-37 (39 figs.). 



j Proc. Amer. Soc. Testing Materials, x. (1910) pp. 518-50 (32 figs.). 



§ Rev. Metallurgie, viii. (1911) pp. 224-40 (34 figs.). 



