IMPROVEMENTS IN METALLURGICAL MICROSCOPES. 



By Albert Sauveur (Harvard University). 



At the kind request of Sir Robert Hadfield, I am submitting 

 this slight contribution to the symposium on the microscope and its 

 applications. Referring first to the minor improvements I have been 

 able to introduce into the construction of metallurgical microscopes, 

 I venture to mention the following points. 



It is, I believe, at my suggestion that microscopes for metallur- 

 gical work were first constructed by the Bausch and Lomb Optical 

 Company, of Rochester, New York, with a stage that could be 

 racked up and down in a manner similar to the substage attachment, 

 thus affording greater working distance, and doing away with the 

 necessity of ever having to displace the vertical illuminator, the 

 condensing train and the source of light as objectives of varying 

 focal lengths are used. It is also at my suggestion that in inverted 

 microscopes and in the vertical-horizontal type herewith illustrated 

 a totally reflecting prism was attached to a horizontal draw tube, 

 affording a ready means of pushing it in or drawing out of position 

 as desired. 



The two types of metallurgical microscopes used almost exclu- 

 sively in the United States are shown in Figs. 1 and 2, special 

 attention being called to what may be called the horizontal-vertical 

 type (Fig. 1), in which a vertical microscope is used for visual 

 work, while a permanently connected horizontal camera is used 

 for photographic work. It is believed that this arrangement presents 

 some decided advantages over the vertical type as well as over the 

 inverted type. I do not believe that these instruments have ever 

 been surpassed by those of German manufacture. 



The magnetic holder which I designed many years ago for 

 holding iron and steel specimens has proved, I believe, very service- 

 able, and is widely used in the United States. 



As to the directions in which metallographic investigation should 

 be stimulated as more likely to bring valuable results, I am not 

 one of those who believe that much is to be expected from examina- 

 tion at greatly increased magnifications. Confining my remarks 

 to iron and steel, with the exception of the occurrence of carbon, we 

 are still greatly handicapped by the lack of methods by which other 

 constituents and impurities can be identified and their occurrence 

 studied, and it seems to me that we should endeavour to remedy 

 this condition. Let us briefly consider the various elements or 

 chemical compounds present in industrial iron-carbon alloys. 



Carbon. — We have at our command satisfactory means of distin- 

 guishing under the microscope the various forms in which carbon 

 occurs in these alloys. I am not of the opinion that carbon may be 

 present, as some believe, in a much greater number of varieties 

 than we are now able to identify, and I do not believe that examina- 

 tion under greatly increased magnification or other methods would 

 advance much further our knowledge of the behaviour of that vital 



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