THE INACTIVE ELEMENTS: RADIUM AND RADIO-ACTIVITY 43 Argon, helium, krypton, neon, and xenon. Radium. Disintegration theory of Rutherford and Soddy. Actinium and polonium. The emanations. CHAPTER IV ATOMS AND MOLECULES: ATOMIC WEIGHTS AND EQUIVALENTS 61 Hypothesis of Avogadro. Stanislao Cannizzaro. Determination of molecular weights. Applicability of law of Dulong and Petit. Relations of molecular weight to osmotic pressures. Determination of atomic weights. Hypothesis of Prout, Dumas, Stas, Lord Rayleigh, Leduc, Morley, Guye, Theodore Richards. Validity of law of conservation of mass: Landolt. CHAPTER V THE MOLECULAR THEORY OF GASES 79 Interdependence of the gaseous laws. Kinetic theory of gases: Bernoulli, Waterston, Clausius, Maxwell, Boltzmann, Schmidt, Graham. Gaseous diffusion. Van der Waals’s equation. Ratio of specific heats: Kundt and Warburg. Liquefaction of gases. Critical temperatures and pressures: Andrews, Pictet and Cailletet, Wroblewski, Olszewki, Dewar, Kammerlingh Onnes. Liquefaction of air on the large scale. Research at low temperatures. CHAPTER VI THE PERIODIC LAW 101 Prout, Thomson, Döbereiner, Newlands, De Chancourtois. Statement of the Periodic Law by Mendeléeff and Lothar Meyer. Its importance as a system of classification. CHAPTER VII VALENCY 112 Origin of conception of Valency: Williamson, Gerhardt, Frankland, Couper, Kekulé. Tetravalency of carbon and linkage of atoms. Rational and constitutional formulæ. Dynamical theories of valency. CHAPTER VIII THE CHEMISTRY OF AROMATIC COMPOUNDS 119 Peculiarities of aromatic compounds. Kekulé’s benzene theory. Its applications. The essential oils. Terpenes. Camphor. Synthesis of perfumes. Alkaloids. CHAPTER IX STEREO-ISOMERISM: STEREO-CHEMISTRY 138 Opticity: Biot, Mitscherlich, Pasteur, Wislicenus, Van ’t Hoff, Le Bel. Asymmetry. Racemisation. Multirotation. Geometrical isomerism. Geometrical inversion. Stereo-isomerism among nitrogen, sulphur, selenium, tin, and silicon compounds. Tautomerism. Steric hindrance. CHAPTER X ORGANIC SYNTHESIS: CONDENSATION: SYNTHESIS OF VITAL PRODUCTS 152 Use of specific condensing reagents. Carbon suboxide. Artificial preparation of naturally occurring substances. Synthetic medicines. The ptomaines. Artificial alizarin. Indigo. The sugars and proteins: Emil Fischer. The doctrine of “vital force.” CHAPTER XI