Xii CONTENTS 



Page 



Micrometry by means of a scale projected by the Abbe condenser 187 



Use of the micrometer fine adjustment 190 



Measurements of thickness 191 



Practical applications of micrometric measurements 191 



CHAPTER VIII. 



Quantitative Analysis by Means of the Microscope. 



Methods available 198 



Analysis of powdered material 200 



Net ruled oculars and their uses 202 



Counting cells ._ 205 



Sampling 204 



Determination of weight by micrometry 209 



Volume and weight per cents; area measurements 212 



Estimation of molecular weight 213 



Micro-colorimetry 215 



CHAPTER IX. 



The Determination of Melting and Subliming Points. 



Approximate methods 219 



Exact methods 220 



Hot stages 222 



Subliming points ^ 225 



CHAPTER X. 



The Determination of Refractive Index by Means of the Microscope. 



The relation between refractive index and contour bands 226 



Principle of the immersion method 226 



Behavior of air bubbles and oil globules 228 



Half-shadow method of illumination 231 



Refractive index of anisotropic crystals 234 



Uniaxial and biaxial crystals 236 



Determination of the refractive index of liquids 243 



Determination of thickness by refractive index 244 



Liquids for use in the immersion method 244 



Crystals for use in the immersion method 247 



Refractive indices of typical crystals 248 



CHAPTER XI. 



Crystals under the Microscope. 



Fundamental principles of crystallography 249 



Elements of optical crystallography 252 



