JOUKNAL 



* OF THE 



ROYAL MICROSCOPICAL SOCIETY. 



FEBRUARY 1902. 



TRANSACTIONS OF THE SOCIETY. 



I. — Report of a Demonstration of the Methods used in the 

 Photomicrography of Iron and Steel. 



By William H. Merrett, Assoc. E.S.M., F.C.S. 



(Bead March 20th, 1901.) 

 Plates I. and II. 



The photomicrography, or, as it is now more frequently termed, the 

 " metallography " of iron and steel, has of late years received much 

 attention from eminent engineers and metallurgists ; for it is possible 

 by the aid of the Microscope not only to determine the amount of 

 carbon in the metal, but also to ascertain the exact thermal treat- 

 ment it has received during its manufacture. 



It appears that the metallography of iron and steel has not been 

 developed from petrography, but is a natural extension of the study 

 of meteoric irons. Dr. Sorby, who was one of the first to work 

 on this subject, established a method of examining opaque bodies 

 under the highest powers of the Microscope, and applied this method 

 to different products in the metallurgy of iron. Professors Marten 

 and Wedding were probably the first to systematically examine iron 

 and steel under the Microscope. Recently M. Osmond, of Paris, has 

 done much to develop the science of metallography, and has given us 

 methods by which reliable results may be rapidly obtained. During 

 the past few years much advance has been made in the subject, and 

 already many laboratories in steel-works are fitted with photo- 

 micrographic apparatus. 



Although it is possible, by the aid of the Microscope, to learn 

 much about the chemical composition of the metal under examination, 

 it is nevertheless not for this purpose that the Microscope is especially 

 useful. Many samples of steel, having identical chemical compo- 

 sitions, vary enormously in mechanical properties ; and it is by the 



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