Micro-Metallography. By J. B. Stead. 281 



the massive state in steel, and considering that no other reagents 

 yet employed have succeeded in causing it to become tinted, these 

 must be regarded as valuable additions to our etching fluids. 



Professor Heyn has used a 10 p.c. solution of double chloride 

 of copper and ammonium for the purpose of developing the crystal- 

 line structure of iron, a reagent which has been proved to be of 

 great value and service, and is recognised as a standard reagent by 

 many workers. 



Messrs. Heycock and Neville have found that in the study of 

 the bronzes, ferric chloride in alcohol is a most valuable reagent 

 for the development of the structures of such alloys. 



M. G. Charpy and others have used the electrical method 

 of etching with advantage, in which the specimen is attached to 

 one of the poles of a battery and immersed in a suitable etching 

 liquid, such as hydrochloric acid, the metal being electrically 

 dissolved from the surface. This method has given very good 

 results in the development of the structure of brasses, and of 

 austenite and martensite in high carbon steels. 



Other reagents, such as the tinctures of hydrochloric acid, 

 nitric acid, and bromine, have been used with success. 



One of the most beautiful methods of revealing the structure of 

 metals consists in heating the brightly polished specimens until 

 they assume oxidation-coloured films. Professors Behrens and 

 Martens and others have been most successful in the application 

 of this method. Professor Cohen has also used it in differentiating 

 the various constituents in meteorites. 



Microscopes foe Metallography. 



Microscopes suitable for metallography are supplied by most of 

 the good makers, and there is no difficulty in obtaining what is 

 required in that direction, but in metallographic work the Micro- 

 scope does not require any substage, and the stage itself should be 

 arranged in such a way as to be capable of being racked down- 

 wards so as to admit of giving a large space between the object- 

 glass and the object itself. Indeed, an ideal Microscope is one in 

 which a gap of 8 in. can be made. The reason for this is — it 

 often happens that it is necessary to use very low power objectives, 

 and to obtain a wide field of vision. Many makers have introduced 

 Microscope stands with vertically movable stages, and , these are 

 found in the stands of Messrs. Reichert, of Vienna ; Messrs. Beck, 

 Limited, Messrs. Watson and Sons, and Mr. Carl Zeiss, of London, 

 as well as in the Microscopes used by Mr. Sauveur, of Boston, U.S.A. 



