1900] MICROSCOPICAL JOURNAL. 281 



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, first estab- 

 lished a method of examining opaque bodies under the 

 highest powers of the microscope, and applied this meth- 

 od to different products in the metallurgy of iron. Pro- 

 fessors Martens and Wedding were probably the first to 

 systematically examine iron and steel under the micro- 

 scope. Recently, M. Osmond, of Paris, has done much to 

 develop the science of metallography, and has given us 

 methods by which reliable results maybe rapidly obtain- 

 ed. 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 compositions vary enor- 

 mously in mechanical properties, and it is by the aid of 

 the microscope that the cause of these variations may be 

 explained. Metallography is intended to augment, rath- 

 er than supplant, chemical analysis. The microscope en- 

 ables us to ascertain much about the meehanicar and the 

 thermal treatment the metal has received, which in com- 

 merce is often of the utmost importance. Minute blow- 

 holes, cracks, slag flaws and allotropic changes may also 

 be easily detected by its aid. 



The specimens for examination are generally prepared 

 by removing sections from the original sample about 

 three-quarters of an inch square and a quarter of an inch 

 thick. One surface is then carefully ground on a series of 

 emery papers, mounted on plate glass, using ultimately 

 the finest grades which can be produced. As the finest 

 commercial papers are much too coarse, it is necessary to 



