6 CONTENTS 



PAGE 



2. MOLECULAR WEIGHT DETERMINATION IN DILUTE 



SOLUTIONS 27 



A. The theory of dilute solutions 28 



1. Henry's law and the constitution of the dissolved gas . . 28 



2. Avogadro's law for dissolved substances . . . 31 



B. Methods for molecular weight determination of dis- 



solved bodies 36 



1. Direct methods for molecular weight determination of 



dissolved bodies ......... 36 



(a) Comparison of the osmotic pressure of different solutions 



(Isotony) 36 



(6) Absolute measurement of osmotic pressure ... 39 



2. Indirect methods for molecular weight determination . 41 



(a) The cyclic process can be carried out at constant 



temperature 42 



Molecular weight determination by vapour pressure 



measurement ........ 42 



Deduction of the law of diminution of vapour pressure 



without thermo-dynamics . . . . .43 

 Thermo-dynamic deduction of the law of diminution of 



vapour pressure 46 



Abnormal values for abnormal vapour densities . . 47 



Accuracy attainable in measuring vapour pressures . 49 



Molecular weight determination by lowering of solubility 50 

 Ratio of partition . . . . . . .53 



(b) The cyclic process cannot be carried out at constant 



temperature ........ 54 



Molecular weight determination by lowering of the 



freezing point ........ 54 



Molecular weight determination by the rise of boiling 



point 57 



Molecular weight determination by means of the change 



of solubility with temperature .... 58 



C. Results 59 



1. Simple molecular magnitude of dissolved bodies ... 59 

 Larger molecules. Agreement with the results of gas density 



measurements ...... 59 



Larger molecules in hydroxylic compounds .... 60 



2. Development of the stereochemical conceptions . . .61 



3. Abnormal results for isomorphous compounds . . .61 



4. Abnormal results for electrolytes 62 



The theory of electrolytic dissociation ..... 62 



Electrolytes which follow Ostwald's law of dilution . . 66 



Electrolytes which do not follow Ostwald's law of dilution . 67 



