184 SCIENCE PROGRESS. 



residue of constant composition which was not a chemical 

 compound. 



The microscope promises to become as important to 

 the student of metallurgy as it has long been to the 

 geologist, the connection between the mechanical pro- 

 perties of an alloy and its microscopic structure being a 

 very close one. The work of Osmond and others on the 

 microscopic structure of steel deals with a material too com- 

 plex for adequate discussion here, and of the valuable treatise 

 by Behrens on the minute structure of alloys, the same must 

 be said. However the results obtained by the last-named 

 writer, by Guillemin, 1 and by Charpy, 2 present certain 

 general features. Guillemin etches the polished surface 

 of a brass or bronze with dilute sulphuric acid ; the etched 

 surface is then examined microscopically, and the image 

 photographed. Different alloys give very different sur- 

 faces, but the same alloy gives a surface of constant character. 

 It presents more or less twisted furrows separated by parts 

 standing out which the acid has spared. He says "it is 

 certain that at the moment of solidification the metal under- 

 goes a liquation, and separates into several alloys of definite 

 composition, which are unequally attacked by the acid ". 



Charpy applies Guillemin's method, with modifications, 

 to the study of brass, and concludes that the brass is formed 

 of two alloys, one being crystalline and the other amorphous. 

 When the alloy is heated the crystals begin to lose their 

 shape at 700', and at a rather higher temperature zinc vola- 

 tilises from them. He utilises electrical action to brino; 

 about the etching, making the brass surface to be etched 

 the zincode of a Daniell's cell. This method of effecting 

 fractional solution appears a promising one. 



Behrens in his work on Das Mikroskopische Gefiigc der 

 Metal le unci Legierungen gives a vast amount of information 

 on this subject. He etches either the natural surface or a 

 polished section of the metal with a variety of solvents, and 

 also brings out texture by partial oxidation produced by heat. 

 The appearance of structure in the alloys he examined 



1 Comptes Rendus, 115, p. 232, 1892. 



2 Ibid., 116, p. 1 131, 1893. 



