The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918
Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.
The actual yield of indigotin from the plant during the manufacture is not discussed by Rawson (loc. cit.), but this author considers that if the suggestions enumerated in his report are adopted, there is little or no room for a remunerative alteration of the process. Bergtheil, on the other hand, considers that under the conditions he describes (1906, 12) the efficiency is represented by an 82 per cent, yield, or that if to this be added the 5 per cent, believed by Rawson to be retained by the extracted plant, 87 per cent, is thus accounted for. The quantity of indigo estimated refers to the precipitate present in the vat after oxidation, and from this must be, therefore, deducted the indigo (10 20 per cent.) lost by the "running off" of the "seeth" water, so that the actual yield of dry colouring matter may thus represent from 62-72 percent, of the theoretical quantity. Recent experiments, however, indicate that by adding aluminoferric to the oxidation a more perfect settlement of the indigo is to be anticipated (ibid., 1909).
Bloxam (Dalsingh Serai Report, and J. Soc. Chem. Ind., 1906, 25, 735), who examined the daily output of indigo (as pressed cake) from the Pembarandah factory, found that the first cuttings of the plant (Moorhun mahai) represented an approximate value of 0,1495 per cent, of indigotin from the plant, whereas the second cuttings gave a value of but 0,1526. Assigning to the plant the low value of 0,3 per cent., a considerable and serious loss is thus apparent. Moreover, the estimation of the results given by the "isatin" method of leaf estimation, and of the finished cake by the "tetrasulphonate" process (loc. cit.), both of which have been standardised with extreme care, point to a loss during the manufacture much greater than has hitherto been acknowledged (Report to Government of India, 1908).
Apart from the retention of indoxyl by the residual plant in the steeping vat, and the mechanical carrying over of indigo by the "seeth" water, the deficiency of colouring matter is chiefly to be attributed to the conversion of indoxyl into products other than indigotin. Rawson (loc. cit.) has pointed out that if the fermented liquid is allowed to stand before oxidation a considerably decreased yield of indigo is ultimately observed. Thus, on the large scale, by standing for six hours a loss of 16,1 per cent, was apparent. Perkin and Bloxam (loc. cit.) have found as a result of their experiments with pure indican, that this alteration or "decay" of indoxyl takes place not only in this manner during the fermentation process, but they consider that the indoxyl from the moment of its production by the hydrolysis of indican until its final conversion into indigotin is continually suffering this alteration. This peculiar reaction is, according to these authors, considerably inhibited by the presence of acid.
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