24 INTRODUCTORY ADDRESS: 



Tiemann says that originally the term Metallography concerned 

 principally the visual examination of the structure of metals, and 

 hence was divided into Microscopic Metallography, or, briefly, 

 Micrometallography, where Microscopes were used to secure high 

 magnifications, and Megascopic, Macroscopic or Macro-Metallography, 

 where the naked eye or very low magnifications were used. The 

 terms Microscopy and Micrography are also used. 



With reference to Metallographic Examination, Tiemann considers 

 that the methods employed may be classified into : — 



(1) Optical Analysis : Determining the Constituents, struc- 

 tures, forms, appearances, etc., by the eye alone or assisted by 

 suitable magnifying devices. 



(2) Thermal Analysis : A Study of the nature of metals 

 and alloys by means of heating and cooling curves, changes in 

 specific heat, etc. 



(3) Magnetic Analysis : Determination of changes in nature 

 affecting the magnetic properties. 



(4) Physical Analysis: Determination of the properties by the 

 usual methods of testing. 



(5) Chemical Analysis: Both proximate and ultimate ; generally 

 in conjunction with one of the other methods. 



He defines the Microscope as follows : — 



(a) A simple Microscope is one which has only one Lens or 

 set of Lenses ; a compound Microscope has two such 

 systems of Lenses, one near the object (Objective) and 

 the other near the eye of the observer (Eyepiece). 



(b) The binocular Microscope consists of two instruments 

 mounted to give a stereoscopic (perspective) view. 



As regards the minute nature of matters forming metals and alloys 

 of metals, an interesting statement is made by Mr. Zay Jeffries, D.Sc, 

 Cleveland, U.S.A., who, when speaking of the ageing of the non-ferrous 

 metal known as Duralumin, in his paper on "The Micro-mechanism of the 

 Ageing of Duralumin," says that when it is cooled from 500° C.in a 

 furnace, globules of CuAlg large enough to be seen easily with a high 

 power Microscope, are formed. In the same sample, however, some 

 globules are so small as to be hardly distinguishable, and others too 

 small to be resolved are suggested by the non-uniformity of the surface 

 appearance of the section. When it is considered that the smallest 

 globule of CuAlj resolvable with a high power Microscope contains 

 about 2,000,000,000 molecules, it is evident that with rapid cooling 

 sub-microscopic particles of CuAU must be present in large numbers ; 

 in fact, after quenching, the average size of a particle must be sub- 

 microscopic. The whole phenomenon of ageing must, therefore, 

 involve changes which cannot be studied directly with a Microscope. 



The same author has devoted a great amount of time to the 

 study of grain sizes and their measurement in metals. He has 

 contributed several papers to the Faraday and other Societies in 

 this country. Much vahiable information is to be found in the work 

 done by Dr. Zay Jeffries. 



