CHAPTER III 



MICROSCOPIC MEASUREMENTS 



In making critical examinations of powdered drugs, it is 

 frequently necessary to measure the elements under observation, 

 particularly in the case of starches and crystals. 



OCULAR MICROMETER 



Microscopic measurements are made by the ocular microm- 

 eter (Fig. 2i). This consists of a circular piece of transparent 

 glass on the centre of which is etched a one- or two-millimeter 

 scale divided into one hundred or two hundred divisions re- 



FiG. 21. — Ocular Micrometer 



Fig. 22. — ^Stage Micrometer 



spectively. The value of each hne is determined by standard- 

 izing with a stage micrometer. 



STAGE MICROMETER 



The stage micrometer (Fig. 22) consists of a glass slide upon 

 which is etched a millimeter scale divided into one hundred 

 equal parts or lines: each Hne has a value of one hundredth of 

 a millimeter. 



STANDARDIZATION OF OCULAR MICROMETER WITH LOW-POWER 



OBJECTIVE 



Having placed the ocular micrometer in the eye-piece and 

 the stage micrometer on the centre of the stage, focus until 



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