S7 6 SCIENCE PROGRESS 



One task which occupied the attention of chemists during 

 the last century was the " synthesis " of various well-known 

 carbon compounds — that is to say, the discovery of processes 

 whereby these compounds can be built up from their elements 

 in the laboratory without the aid of the processes that go on in 

 plant and animal life. Step by step, as the result of patient 

 researches, the synthesis of many plant and animal products 

 has been effected ; in the case of indigo an important discovery 

 made by von Baeyer and Emmerling of a method of obtaining 

 indigotin from isatin was published in 1870. At that time isatin 

 had not yet been synthesised, but eight years later a method of 

 preparing isatin artificially was published by von Baeyer and 

 thus the synthesis of indigotin was complete. In 1880 von 

 Baeyer published another and more convenient way of attaining 

 the synthesis, and continual additions have now been made to 

 the possible ways of synthesising indigotin; benzene, toluene, 

 and naphthalene being the different starting-points. The 

 methods of obtaining it from naphthalene, a very cheap sub- 

 stance, obtained in the manufacture of coal gas, are those that 

 most threaten the natural indigo; and in July 1897 artificial 

 indigo, most probably made from this source, was introduced 

 into the market by the Badische Anilin und Soda Fabrik. 



Indigo has been manufactured from time immemorial in 

 India, and in the last century its production formed a most 

 important industry carried on by numbers of European planters 

 and giving employment to numerous natives; in 1895-6 the 

 exports by sea amounted to 9,350 tons, valued at £3,570,000, and 

 in 1901 the number of persons employed was given as 173,000. 

 The discoveries of 1880 gave rise to some alarm among the 

 planters, but it was not until the last years of the century that 

 they called in the aid of scientific assistance. With the help of 

 the Government they have been endeavouring to make up for lost 

 time and avail themselves of the methods of modern science. 



In order to improve the indigo industry in respect to both 

 the growing of the plant and the manufacture of indigo from it, 

 the point of primary importance was the question of analytical 

 control. Without analytical methods, capable of accurately 

 determining the amount of indican in the plant and of indigotin 

 in the indigo products, the results of field experiments to 

 improve the yield of indican and of attempts to ensure the 

 maximum yield of indigotin in the course of manufacture could 



