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.
Until the last few years the I. sumatrana appears to have been exclusively employed in the best-conducted factories in India. According to Leake (Report of the Dalsingh Serai Research Station, 1903-1904) this is a mixture of several sub-varieties of different values. In this, as in apparently all other indigo plants, the indican exists exclusively in the leaf, though Bloxam and Leake (loc. cit.) point out that the midrib or rachis also contains the glucoside. For the manufacture of indigo the main points in connection with the plant are the weight yielded per acre, the percentage of leaf present, and the indigotin producing value of the latter. According to Rawson ("Cultivation and Manufacture of Indigo," loc. cit.) the good plant contains 40 per cent, of leaf, though occasionally, but not often, the proportion of leaf rises to as much as 60 per cent. Bloxam and Leake found, however, much higher values, 51,7-61,6 on ordinary Indian plant, and 65 per cent, given by twelve experimental plots, figures which include the rachis. Bergtheil (Report of the Indigo Research Station, Sirsiah, 1906, 8) found the percentage of leaf to be 40 per cent., and never higher than 45 per cent.; but, on the other hand, in a redetermination, Leake (J. Soc. Chem. Ind., 1907,26, 1174) records the value as 62,2 percent. Rawson, who conducted numerous analyses of the leaf by his persulphate process (loc. cit.), shows that the indican content as expressed by indigo yielding capacity varies at different periods of the year. Thus, whereas in one instance on May 28 the figure was 0,20 per cent., on August 25 this had risen to 0,76 per cent, of indigotin. Though the leaf on a young plant gives but a small percentage of colouring matter, yet as the plant grows the new leaf contains more colouring principle than the old on the same plant. As an example, on one occasion the percentages of indigotin recorded with new and old leaf were respectively 0,71 and 0,35 per cent. Finally, there is a gradual increase in colouring matter given by leaves from the bottom of the plant upwards as represented by the figures 0,30, 0,44, and 0,62 per cent, respectively. According to Bergtheil (Report of the Indigo Research Station, 1907, 3) the "indigotin content" of the plant is rarely so high as 0,3 per cent. Though the leaf, as a rule, contains a maximum of colouring matter from about the middle to the end of August, it does not necessarily follow that this is the best period for manufacture, as by this time the plant will usually have lost a considerable portion of leaf (Rawson). The manufacture, indeed, usually commences about the middle of June. Gaunt, Thomas, and Bloxam (J. Soc. Chem. Ind., 1907, 26, 1174) refer to a sample of the air-dried leaves of the I. sumatrana, which, in comparison with other dry samples of the same variety (0,6 approx.) and of the Java plant, I. arrecta (1,81 per cent.), yielded indigotin to the value of 3,53 per cent., and consider that this indicates that by selection and suitable methods of cultivation it should be possible to obtain an average plant of greater indigo-producing power than has hitherto been the case.
The plant formerly employed by the Java planters was the I. secundiflora, "Guatemala plant," but for several years past this has been replaced by the I. arrecta or "Natal plant". The latter, it is stated, contains not only more leaf than the ordinary Indian plant, but, as a rule, the leaf yields also a considerably larger percentage of indigo. More recently the Indian planters have recognised the value of the I. arrecta, and accounts are given by Coventry (Indigo Improvements Syndicate Report, 1901) of experiments in connection with its introduction. Leake (Dalsingh Serai Report, 1905) discusses the difficulties of the germination of the seed of the Natal-Java plant, which is due to the impermeable character of the seed coat. This defect, it is pointed out, can be overcome by a process of scratching, and a practical method for this purpose is described. Bergtheil (loc. cit.), in conjunction with D. L. Day, treats the seed with strong sulphuric acid, which leads either to a swelling of the seed coat and its eventual rupture or converts it into a body akin to cellulose and permeable to water. Analyses of the indigo-yielding power of this leaf by Rawson (loc. cit.) gave figures up to 0,96 per cent., whereas Bergtheil (loc. at., 1906) finds in comparison to the I. sumatrana (0,585) that the I. arrecta produced 1,05 per cent, of colouring matter. The percentage of leaf given by the latter averages 52,2 per cent. Again, in 1909 the yield from 100 maunds of the I. arrecta was 15 seers 10 chittacks, as against 11 seers 14 chittacks from the same quantity of the I. sumatrana. The Natal plant is now established in India, and its value appears to be fully recognised. According to Bergtheil (1907) the indigo made from the Java plant has generally been of a high indigotin content, and (1906) that whereas the yield of indigo per acre was 12,6 "seers," that given by the I. sumatrana was by comparison only 8 seers.
A full account of much detailed work on the cultivation of the indigo plants by Rawson, Bloxam and Leake, and Bergtheil is given in the reports above enumerated (cf. also Bergtheil, ibid., 1908-1911).
Ei kommentteja :
Lähetä kommentti