An essay on the culture and manufacture of indigo : to which was awarded the prize of eight hundred rupees by the Madras Government, 1860 / by John Shortt.

  • Shortt, John
Date:
1860
Catalogue details

Licence: Public Domain Mark

Credit: An essay on the culture and manufacture of indigo : to which was awarded the prize of eight hundred rupees by the Madras Government, 1860 / by John Shortt. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    Chemical changes. ing and beating carefully attended to. The best precipitant is a thorough beating, which is necessary to give tho liquid abundance of fresh air, so that the dye should become fully oxidized by combination with oxygen from the air then, its own weight will precipitate it to the bottom of the vat. The apparent gain said to be obtained from the use of lime- water or ash-water is nothing beyond the additional weight of earthy matter and other impurities which interfere with the quality of the dye and thus reduce its market value. It is necessary here to brieflj' describe the chemical changes which are supposed to take place, and to state the objects kept in view in the different processes necessary in the manufacture of the dye. Opinions of chemists arc divided on this subject, and the chemistry of the process has not as yet been correctly ascertained: one set of chemists A ^of °pmi°n °n thc believe that in the Indigo plant the dye exists in combination with cither an acid or an alkali which keeps it colorless until it has been separated from this com- bination ; another set assert that Indigo does not exist in thc plant, but that it is formed during the manufacture by a peculiar process while fermenting. The generally received opinion, however, is that boiling reduces thc plant into its primary simple constituents, prior to the changes which attend their final resolu- tion into water, carbonic acid and ammonia. The usual process of fer- mentation operates much in the same way as boiling, but it is not quite so manageable. These changes areas follows: thc water, assisted by heat, penetrates the immediate particles of the plant and dissolves thc gum as well as the gum-resinous sap ; at the same time thc alkalijand oil, aided by heat, unite and form soap ; this mixes with the gum solution natural to the plant, and renders the fluid saponaceous and opalescent; it is then sufficiently consistent to hold thc resin or dye in suspension in the form of innumerable spherical globules. It is well known that the sap of the Indigo plant contains, besides salts, oil and resin, gum and other substances which arc of a mucila- ginous nature; and though the dye or resip itself is insoluble in water, the ebullition favors its formation into a mucilaginous and saponaceous fluid sufficiently thick to enable it to retain the resinous d}m in solution. Tho formation of the soap assists, no doubt, in the separation of the resinous dye from the salts and oil contained in thc plant, which unite to render thc fluid saponaceous. Thc union of thc dye resin with tho Supposed chemical changes.
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