CHAPTER III 

 MICROSCOPES FOR USE IN CHEMICAL LABORATORIES. 



The problems which the chemist is called upon to solve where 

 the microscope is of great value, if not actually essential, are 

 so diverse in their nature and the materials to be examined so 

 varied in size, outward form, structure and composition that it 

 is safe to say that no single instrument will ever be constructed 

 which will meet all requirements and fulfill all conditions. Before 

 deciding upon any given style or model of instrument the in- 

 tending purchaser should, therefore, first carefully consider the 

 kind of work his instrument will most frequently be called upon 

 to perform. 



A microscope for microchemical analysis and applicable to 

 the ordinary problems arising in the chemical laboratory should 

 fulfill the following requirements : 



1. The stand should be substantially built so as to be easily 

 and safely carried about. It should permit the attachment of 

 the usually employed accessories, such as a mechanical stage, 

 Abbe condenser, camera lucida, polarizing apparatus, etc. A 

 hinged pillar allowing the inclination of the microscope is a 

 valuable feature and a great convenience. In a vertical position 

 for work the stand should be low enough to permit observations 

 being made in comfort, without the necessity of having either 

 specially high stools or low tables. It is desirable that the in- 

 strument be entirely finished in black and have as few bright 

 reflecting surfaces as possible. 



2. There should be coarse adjustment by diagonal rack and 

 pinion of as great range as possible. When the movement of 

 the rack is short the usefulness of the microscope is greatly 

 restricted, since low powers cannot then be used with thick ob- 

 jects. A sensitive fine adjustment is also an essential, and if the 

 fine adjustment is provided with micrometer screw and gradu- 



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