Open main menu
This page needs to be proofread.
485
INDIGO

inadequate compilations in 1596 and 1628, and finally the great Recopilacién de Leyes de los Reinos de las I ndias of 1680. This code has enjoyed great fame, and in some ways even extravagant praise. The greatest praise that has been given it is that its dominant spirit through and through is not the mercantile aim but the political aim-the principle of civilization; and this praise it deserves. It had various defects, however, of an administrative nature; and as time passed its basic doctrines especially its minute administrative strangulation of colonial political life, and its monopolistic economic principles-became fatally opposed to conditions and tendencies in the colonies. Two centuries in formation, the code of 1680-continually altered by supplementary interpretation and application was only one century in effect; for in the seventeen-sixties Charles III. began, in a series of liberal decrees, to break down the monopolistic principles of colonial commerce. This change came too late to save the mainland colonies in America, but its remarkable effects were quickly seen in the aggrandizement of Cuba. It is in the history of this colony (as also in Porto Rico and the Philippines) that one must follow the later history of the Laws of the Indies (see CUBA).

Of the Recopilacién of 168O, five editions were issued by the government, the last in 1841 (Madrid, 4 vols.); and there are later, private editions approved by the government. See also J. M. Eomora y Coronado, Biblioteca de legislation Ultramarina (Madrid, 1844-1849, 6 vols., with appendices often bound as vol. 7); ]. Rodriguez San Pedro, Lcgislacion Ultramarina coucardada, covering 1837-1868 (12 vols., Madrid, 1865-1868, vols. 10-12 being a supplement); the Boletin of/Icial del Minjsterio de Ultraman, covering 1869~187Q; and Fernandez Martin, Comptlaczoa legzslatwa de golnerno y admimstracion cwzl de Ultramar (Madrid, 1886-1894); the gap of 1879-1886 can be filled for Cuba by the series of Reales Ordenes. . . publiradas en la Gaceta de la Habana (annual, Havana, 1857-1898, covering 1854-1898).


INDIGO (earlier indico, from Lat. indicum, the Indian substance or dye; the Sans. name was niti, from nila, dark blue, and this through Arab. al-nil, annil, gives “ aniline ”) one of the most important and valuable of all dyestuffs. Until comparatively recently it was obtained exclusively from the aqueous extract of certain plants, principally of the genus Indigofera which belongs to the natural order Leguminosae. Small quantities are also obtained from Lonchocarpus eyanescens (west coast of Africa), Polygonum tinlarium (China) and the woad plant I satis tinctoria. The latter is of historical interest since up to the middle of the 17th century it was the only blue dyestuti used by dyers in England and on the adjoining continent; at the present time woad is still cultivated in Europe, but serves merely as a ferment in the setting of the fermentation indigo vat or so-called “ woad vat ” used in wool dyeing. The bulk of the natural indigo which is brought into the market comes from India, while smaller quantities are imported from java, Guatemala and other places. The plant from which indigo is made in Bengal is the Iudigofera sumatrana, which is reared from seed sown about the end of April or the beginning of March. By the middle of June the plant has attained a height of from 3 to 5 ft., and it is at this period that the first manufacturing begins, a second crop being obtained in August. The indigo is contained in the leaf of the plant in the form of a colourless glucoside, known as indican, CMHUOGN-3H2O. his substance is soluble in water and by the joint action of an enzyme, contained in the leaf, and atmospheric oxygen it yields indigo tine, the colouring matter of indigo. It is on these facts that the manufacturing of indigo from the plant is based. The plant is cut early in the morning and transported to the factory in bullock carts. Here it is steeped in water in steeping vats having a capacity of about 1000 cub. ft. for periods varying, according to circumstances, from nine to fourteen hours, when the liquid-the colour of which varies from a bright orange to an olive green-is run into the beating vats which lie at a lower level. The beating, the object of which is to bring the liquor as freely as possible into contact with the air, was formerly done by striking the surface with bamboo sticks, but is now effected either by means of a paddle wheel or by forcing a current of air from a steam blower or a compressor through the liquid. 7

When the beating is finished, the precipitated indigo is allowed to settle, the supernatant liquid being drawn off and run to waste. The indigo mud thus obtained, which is known as mal, is strained, boiled for a short period for the purpose of sterilizing, formed into bars, cut into blocks of about 3 in. cube and dried! The actual amount of colouring matter yielded by theleaf is but small, averaging, according to Ch. Rawson, o~5 %, but the yield from the whole plant is considerably less, since the stalks and twigs contain practically no colour.

Since the introduction on a large scale of synthetic indigo efforts have been made in India and in lava to place the cultivation of the plant and the manufacture of the natural product on a more scientific basis. But although many important improvements have been achieved from the agricultural as well as from the manufacturing point of View, resulting no doubt in the re tension of a portion of the industry, the synthetic product has gained the upper hand and is likely to retain it. Natural indigoes vary considerably in composition, containing in some qualities as much as 90% and in others as little as 20% of colouring matter. The blue colouring matter which indigo contains is known as indigo tine, but there are usually also present in small quantities other colouring matters such as indigo red or indirubrine, a yellow colour known as kaempferol, indigo green and indigo brown, as well as indigo gluten and more or less mineral matter.

The bulk of the indigo which now comes into the European market is prepared synthetically from coal tar. The following figures indicate the values of the imports into England of natural and synthetic indigo, and are taken from the official Board of Trade returns:-

Natural Indigo. Synthetic Indigo

1899 £986,090 . .

1900 542,089 . .

1901 788,820

1902 498.043 £143,513

1903 262,775 1 I0»970

1904 3101070 33,397

1905 116,902 121,269

-1906 I I 1,455 147,325

1907 151,297 158,481

I 1908 136,882 134,052

During the period 1899-1908, the average price of 1nd1go had declined from a fraction under 3s. to about zs. zéd. per lb. At first sight it might appear that the use of indigo in England was rapidly declining, but this does not necessarily follow when it is borne in mind that London was formerly the distributing centre of natural indigo for the continent and America. Chemistry.-Our knowledge of the chemistry of indigo is largely derived from the classical researches of A. von Baeyer and his collaborators. In 1841 Erdmann and Laurent observed that on oxidation indigo yielded isatin; and in 1848 Fritzsche obtained aniline by distilling the dyestuti' with potash. In 1870 A. v. Baeyer and Knop succeeded in preparing indigo tine by heating isatin with phosphorus trichloride, acetyl chloride and phosphorus. In the same year, C. Engler and A. Emmerling obtained small quantities of the dyestuff by heating nitroacetophenone with soda-lime and zinc dust, while in 1875 M. v. Nencki prepared it by the oxidation of indol by ozone. Indol had been previously obtained from albuminoids by means of the pancreas ferment. It was not, however, until 1880 that v. Baeyer, who had been at work on the subject since 1865, was able to obtain indigo tine from more or less easily accessible coal tar derivatives of known constitution. The most important of these synthetic processes due to the researches of v. Baeyer was the production of the dyestuff from ortho-nitrophenylpropiolic acid (see PROPIOLIC ACID), which yields indigo tine on being treated with caustic soda and a reducing agent such as grape sugar or xanthate of soda. Although used in small quantities in calico printing, it never attained any commercial importance as a means of producing indigo, the cost of production being far too high.

Many synthetic processes of preparing indigo tine have since been devised, but the one which stands out pre-eminently from a technical point of view and the one which ultimately led to the commercial success of the synthetic product is that of Heumann who showed in 1890 that indigo tine can be prepared by melting phenylglycocoll

For a full account of the manufacture of indigo in northern Behar see Ch. Rawson, Journ. Soc. Dyers and Colourists (July 1899).