ON THE DEVELOPMENT OF PHYSICAL CHEMISTRY SINCE 1850 171 Molecular volumes of liquids. Nature of solution. Van ’t Hoff’s application of the gas laws to phenomena of solution. Osmosis and osmotic pressure. Traube. Pfeffer. Semi-permeable membranes. Measurement of osmotic pressure. Arrhenius. Doctrine of ionisation. Its applicability to the explanation of chemical phenomena. Thermo-chemistry. Mass action. Nature of reversible reactions. Thermal and Electrolytic dissociation. Relation between chemical nature and opticity, magnetic rotation and viscosity. Theory of phases. Catalysis. Enzyme action. Relations between valency and volume. Photochemistry. BIBLIOGRAPHY 187 INDEX 191 ILLUSTRATIONS PAGE JUSTUS VON LIEBIG _Frontispiece_ JEAN BAPTISTE ANDRÉ DUMAS 9 THOMAS GRAHAM 13 From a painting by G. F. Watts, R.A., in the possession of the Royal Society ALEXANDER WILLIAM WILLIAMSON 15 BUNSEN, KIRCHHOFF, AND ROSCOE 19 SIR WILLIAM RAMSAY 48 MARIE CURIE (_née_ SKLODOWSKA) 56 STANISLAO CANNIZZARO 65 SIR JAMES DEWAR 98 DMITRI IVANOWITSCH MENDELÉEFF 110 AUGUST KEKULÉ VON STRADONITZ 126 JACOBUS HENRICUS VAN ’T HOFF 142 EMIL FISCHER 166 SVANTE AUGUST ARRHENIUS 180 HISTORY OF CHEMISTRY CHAPTER I STATE OF CHEMISTRY IN THE MIDDLE OF THE NINETEENTH CENTURY