All About Inventions and Discoveries
The Romance of modern scientific and mechanical Achievements

The Story of Coal-Gas 61 return. Indigo was a dye for which a huge com- mercial demand existed, but the natural article was expensive, and was rising in price. It was virtually a monopoly of India, where it was raised upon an elaborate scale. But human perseverance in due course achieved its object. Artificial indigo was converted into a practical achievement, and, as in the case of the madder, the cultivation of indigo fell upon evil days. It is only recently that the Indian industry has experienced a revival and a new era of prosperity. The successful manufacture of artificial dyes from the by-products of coal-gas distillation have wrought many changes, some of which are somewhat inter- esting. Thus, Tyrian purple was a highly expensive colouring medium until the aniline dye of this tinge appeared upon the market. The natural article was derived from the blood of shellfish, and, as may be supposed, its production under these curious cir- cumstances was extremely costly, and obtainable only in limited quantities. To-day the synthetic dye, which has completely displaced the natural article, can be manufactured cheaply and upon an extensive scale. The story of aniline dyes forms a fascinating romance in itself. At the moment there are a round thousand different colours which are supplied from this by-product of the gasworks. Each has its individual story of patient investigation, and each represents a distinct conquest of chemical science. Hand in hand with the extraction of aniline dyes from coal tar has marched the derivation of drugs which are used on every side—such drugs as aspirin, antipyrin, veronal, sulphonal and so forth. Then,