RESEARCH AND THE COAL-TAR DYE INDUSTRY 415 



Several years' further work was devoted to the problem, 

 but finally it was decided that Heumann's method was of no 

 technical use, and in 1897, after seventeen years' co-operative 

 research and the expenditure of over half a million sterling, 

 the agreement was dissolved and each firm decided to go its 

 own way. 



The Hoechst works nevertheless succeeded in producing 

 some quantities of indigo from anthranilic acid obtained from 

 ortho-nitro-toluene . 



In this connection an interesting point arises : if toluene 

 were taken as the starting-point for the syntheses of indigo, 

 the former must, of course, be obtained from coal-tar, of 

 which it forms only a small proportion, the chief components 

 being benzene and naphthalene. Now the annual production 

 of crude benzene amounted then to some 25,000 to 30,000 

 tons per annum, of which only some 5,000 to 6,000 tons were 

 toluene, which was already in demand for the preparation of 

 benzaldehyde for making malachite green and so on. 



Now by the best methods 1 ton of indigo could not be 

 made from less than 4 tons of toluene, and as the annual demand 

 for indigo was not less than about 5,000 tons, it is obvious 

 that the world's output of toluene could only cover a quarter 

 of this, whilst if the output of toluene were increased to the 

 necessary 20,000 tons, simultaneously there would be at least 

 80,000 tons more benzene to be disposed of besides the pro- 

 duction of a colossal amount of coke for which there would be 

 no use. 



The introduction of benzol as a motor fuel, and the recovery 

 of benzol and toluol from coke-oven gases, has to-day con- 

 siderably altered the state of affairs, but twenty years ago the 

 objections noted were sufficient to decide against the use of 

 toluene as a starting-point. In spite of many difficulties, 

 financial and chemical, the Badische Company produced a 

 certain amount of synthetic indigo, but it was not until 1896 

 that the problem was really solved. 



In this year, shortly before the dissolution of the agreement 

 between the two firms, an accidental discovery settled the 

 matter. Sapper, of the " Badische Anilin und Soda Fabrik," 

 whilst researching on the preparation of phthalic anhydride by 

 oxidising naphthalene with fuming sulphuric acid, by chance 

 broke the thermometer registering the temperature of the melt. 



