4 i6 SCIENCE PROGRESS 



On allowing the mass to cool it was found that instead of 

 the usual poor yield of the product the naphthalene had been 

 converted almost quantitatively into the anhydride owing to 

 the catalytic influence of the mercury. 



It was at once seen that the solution of the indigo problem 

 was at hand. 



The only remaining question now was the cheap production 

 of fuming sulphuric acid as an oxidising agent. 



This difficulty was soon overcome by the researches carried 

 out at the Badische works under the able guidance of Knietsch, 

 by extending and improving the contact process for the manu- 

 facture of the acid from sulphur dioxide and air. 



The process of oxidation may be represented by a scheme 

 thus : 



(Sulphur dioxide + AIR) -> (Sulphur trioxide) 



f 4 



(Sulphur dioxide (Sulphur trioxide 



+ <- + 



PHTHALIC ANHYDRIDE) NAPHTHALENE) 



so that the whole process is realty carried out at the expense 

 of the cheapest of all oxidising agents, namely atmospheric 

 oxygen. Since already by 1900 40,000 tons of sulphur dioxide 

 were produced annually by this process and reconverted into the 

 trioxide (the figures for recent years must, of course, be manj^ 

 times greater), it will be realised what a huge affair this process is. 

 At the same time it was necessary to have large quantities 

 of chlorine and acetic acid to produce the necessary chlor- 

 acetic acid. The acetic acid was produced by the distillation 

 of wood, of which in 1900 over 100,000 cubic metres were dis- 

 tilled for this purpose ; the chlorine was produced by the 

 electrolysis of potassium chloride from the Stassfurt deposits, 

 and was purified by liquefaction according to the method 

 worked out by Knietsch some years previously. In its turn 

 the enormous volumes of hydrogen so produced as a by-product 

 may be utilised either for filling airships, or, as the result of the 

 joint researches of Prof. Haber and of the Badische Com- 

 pany, are caused to unite with the waste nitrogen produced 

 in Linde's process for manufacturing oxygen from liquid air, 

 to give ammonium salts for fertilisers and for the production 

 of nitrates needed to manufacture explosives. 



