Natural Sources of Indigo, 124. Syntheses of the Colouring-matter, 126. Carbolic Oil, its treatment and its constituents, 129. Phenol Dyes, 132. Salicylic Acid and its uses, 134. Picric Acid, 136. Naphthalene and its applications, 139. The Albo-carbon Light, 140. Phthalic Acid and the Phthaleins, 145. Magdala Red, 149. Azo-dyes from the Naphthols, Naphthylamines, and their Sulpho-acids, 150. Naphthol Green, the Oxazines, and the Indophenols, 161. Creosote Oil, 163. The Lucigen Burner, 163. Anthracene Oil, 167. The Discovery of Artificial Alizarin, and its effects on Madder growing, 167. The industrial isolation of Anthracene and its conversion into Colouring-matters, 171. Pitch, and its uses, 176. Patent Fuel, or Briquettes, 178. Coal-tar products in Pharmacy, 178. Aromatic Perfumes, 185. Coal-tar Saccharin, 186. Coal-tar Products in Photography, 188. Coal-tar Products in Biology, 192. Value of the Coal-tar Industry, 194. The Coal-tar Industry in relation to pure Science, 196. Permanence of the Artificial Colouring-matters, 198. Chronological Summary, 200. Addendum, 202. COAL; AND WHAT WE GET FROM IT. CHAPTER I. "Hier [1771] fand sich eine zusammenhaengende Ofenreihe, wo Steinkohlen abgeschwefelt und zum Gebrauch bei Eisenwerken tauglich gemacht werden sollten; allein zu gleicher Zeit wollte man Oel und Harz auch zu Gute machen, ja sogar den Russ nicht missen, und so unterlag den vielfachen Absichten alles zusammen."--Goethe, _Wahrheit und Dichtung_, Book X. To get at the origin of the familiar fuel which blazes in our grates with such lavish waste of heat, and pollutes the atmosphere of our towns with its unconsumed particles, we must in imagination travel backwards through the course of time to a very remote period of the world's history. Ages before man, or the species of animals and plants which are contemporaneous with him, had appeared upon the globe, there flourished a vegetation not only remarkable for its luxuriance, but also for the circumstance that it consisted to a preponderating extent of non-flowering or cryptogamic plants. In swampy areas, such as the deltas at the mouths of great rivers, or in shallow lagoons bordering a coast margin, the jungles of ferns and tree-ferns, club-mosses and horse-tails, sedges, grasses, &c., grew and died down year by year, forming a consolidated mass of vegetable matter much in the same way that a peat bed or a mangrove swamp is accumulating organic deposits at the present time. In the course of geological change these beds of compressed vegetation became gradually depressed, so that marine or fresh-water sediment was deposited over them, and then once more the vegetation spread and flourished to furnish another accumulation of vegetable matter, which in its turn became submerged and buried under sediment, and so on in successive alternations of organic and sedimentary deposits.