Indigo is judged commercially by its lightness, by a copper gloss on the surface, and by exhibiting no foreign ingredients when broken. There are several ways of testing it chemically, to ascertain the exact proportion of indigotine present ; one method is as follows :—Finely pulver ized indigo, 1 part ; green copperas, 2 parts; and water containing 10 per cent. of caustic soda, 200 parts ; are well boiled in a flask, and left to cool. The clear liquor is exposed in shallow vessels to the air, when the soluble indigo is oxidized, and precipitated as pure indigotine. The residue in the flask is thus treated three times ; the whole of the indigotine is then collected on a filter, dried, and weighed. The consumption of indigo is still very large ; our imports, in 1878, were as follows :—From Bengal and Burmah, 45,798 cwt.; Madras, 9674 ; Central America, 7272 ; Bombay and Scindo, 675 ; France, 462 ; Holland, 280 ; Germany, 228 ; other countries, 1114. In 1879 the figures were :—Bengal and Burmah, 38,652 ; Madras, 27,654; Central America, 6685; Bombay and Schick, 2963 ; France, 1241 ; Holland, 409 ; Germany, 354 ; and otheicountries, 2188. Artificial indigo has not, as yet, been manufactured on a commercial scale, nor at a commercial price ; but it has been produced, in the laboratory, from coal-tar derivatives, and further experiment may reveal a process for preparing the article at a sufficiently low price to compete with the natural dye-stuff.
Several preparations of indigo are in use :—(1) Sulpho-purpuric acid, phenicine, or indigo purple, is made by mixing 1 part of indigo with 4 parts of sulphuric) acid (sp. gr. 1.845), and heating for hour ; the acid mass is thrown into 40-50 parts of water, when the purple falls down ; it is collected on a filter, and washed with dilute hydrochloric acid ; (2) Sulphindigotio acid is prepared by mixing indigntine, 1 part, with sulphuric acid (sp. gr. 1.845) 6 parts ; the operation must bo performed in a leaden vessel, cooled outside, and the indigo must be added by degrees, to avoid heating ; the mixture is then left for 8 days, when the conversion will be complete. Fuming or anhydrous acid may be used, in less proportion, but the reaction is more difficult to manage. Weaker acid will require a longer period, say a month for "brown acid" (145° Tw.); (3) The suiph indigotic acids are transformed into neutral paste, or "carmine," by neutralizing with carbonate of soda, and washing the paste, on a woollen filter, with a solution of chloride of sodium.
Satztala.—The fruits of Rottlera tinctoria (MaRotus, Croton, Echinus Philippinensis)are closely beset with ruby-like glands, whioh, when removed, constitute the powder known by the above name. It forms one of the minor products of the Government forests in Madras Presidency, and is also collected in many other parts of India. The berries are gathered in large quantities, and thrown into baskets, where they are rolled and shaken about, to thoroughly divest them of the powder, which, escaping through the wickerwork, is caught on a cloth spread beneath. In the
N.-W. Provinces, the harvest commences in early March, and lasts for about tt. month. A little adulteration is practised by means of powdered leaves and stalks, and earthy matters. The product is in great repute as an anthelminthie, but is used ohiefly as a dye. S. Arabia produces a similar powder, which is exported to Bombay and the Persian Gulf. A very peculiar form of the substance has been imported (via Aden) from Harttr, in Somali-land, under the name of Wars, or Wurrus, a term properly oonfined to saffron. Its origin is uncertain ; it is largely used, on the Muscat and Hadramaut coasts, in medicine and as a dye ; Aden exported about 43,000 lb. of it in 1875-6. Fine Kamala is often adulterated largely with earthy matters ; tt, large quantity in a very impure state was offered in London in 1878, for cleaning polished metal. The tree flourishes throughout India, up to 5000 ft. ; in Ceylon, the whole Eaatern Archipelago, E. China, N. Australia, Queensland, and New South Wales, and in Abyssinia and S. Arabia.
Bermes (Fa., Kermes ; GER., Kermes).—This colouring matter is furnished by several species of Coccus, named after the plants which they inhabit ; it is identical in character with that afforded by cochineal. The most common variety of the inaect is C. ilicis, found as a paraaite on a dwarf species of oak, Quercue coccifera, a native of the whole Mediterranean basin. In England, this dye-stuff has been displaced by cochineal ; but in S. France, Spain, Morocco, and Turkey, it is largely used for dyeing leather and woollens, and in Milan, Rome, and Florence, for colouring beverages. The female insect deposits some 1800-2000 eggs on the leaves and branches of the oak, the amount of the crop depending upon the mildness of the preceding winter. These eggs form excrescences, which are bodily removed just before hatching would take place, usually from mid-May to mid-June. The collecting is performed at early morning, while the dew lasts ; experienced hands may pick 2 lb. in a day. The kermee are immediately exposed to the fumes of heated vinegar ; this destroys their fecundity, and develops a dull reddish-brown colour. The quality and price deteriorate as the season advances. The Spanish product seems to be most esteemed. The Algerian product is chiefly consumed locally, but the exports reach about 4000 lb. yearly. France imports about 6000 lb. annually, for cosmetic and pharmaceutical preparations. The colour is scarcely so brilliant as that of cochineal; but it is unchanged by soap or dilute alkalies. Other descriptions of kermes are afforded by C. Polonicus, found on the roots of Polygonum cocciferum, and other plants, in the sandy soils of Poland, and S.-W. Russia ; by C. fragariel, on roots of the common strawberry, in Siberia; and by C. ura-ursi, in Russia.