INDIGO .
455
the countries whence they are imported :—Asiatic indigos, from Bengal, Oude,Madras, Java, and Manilla. African, imported from Egypt, Mauritius,Senegal. American, from Guatemala, Caraccas, Mexico, Brazil, the Antilles,and South Carolina.
The Bengal, Java, and Guatemala indigos are considered the best; thesevarieties exhibit the following general characteristics :—Java indigo containsgenerally the colouring matter in a very pure state, along with a minimum ofextractive organic matter; but in some of the sorts of this drug the quantityof indigotin is greatly decreased by the amount of siliceous matter present.This indigo feels soft, and adheres strongly to the tongue if pressed against it.The sp. gr. of this material is low ; its colour a pure soft blue, the inferiorqualities exhibiting an ash-grey hue, while the superior qualities are mag-nificently violet-blue, and assume, when rubbed with the nail, a beautifulcoppery hue. The Java indigos, although not the very richest in indigotin,are superior to all others as regards the purity and beauty of the colouringmatter ; they, moreover, contain no carbonate of lime, and are, also on accountof the very small quantity of organic matter they contain, in very high re-quest for the manufacture of indigo carmine. Practical dyers complain thatJava indigos do not work well, their tinctorial value, i.e. the amount of woolthey will dye up to a given shade, being smaller than their appearance, eitherin the lump or in solution, would lead the observer to expeCt.
The Java indigo is imported chiefly, but not exclusively, into Holland, andis packed in very carefully-made wooden boxes, weighing when full from 20 to60 kilos.; the ware is in square or cubical cakes.
Bengal indigo is the indigo par excellence , on account of the yield, in-cluding a great variety of sorts from the richest to the most common. Thisware comes chiefly to London in the shape of large prismatic lumps, packed inwooden boxes, containing from 130 to 140 kilos. The higher qualities are adeep blue violet. The paste is very homogeneous and fine grained; it adheresto the tongue, but less strongly than Java indigo. Bengal indigo is easilypulverised, and exhibits also, when rubbed with the nail, a coppery hue; itcontains on an average about 72 per cent of indigotin. The sp. gr. of indigois on an average, according to M. Ziurek, =0*769, while that of indigotin is= 1*35. The brokers distinguish no fewer than forty-five different kinds of Bengalindigo, among which are certain varieties which exhibit a reddish hue, dueto the presence of a larger quantity of a brown extractive matter, which, indeed,far from acting injuriously on the dyeing operations, seem to exercise a bene-ficial effect, because it appears to assist the fixing of the indigo on the tissues.Dyers very generally prefer the reddish Bengal indigo, but reject the lightblue kind, which has a strong greyish or greenish tint, and is hard and dense,containing a large amount of an inert extractive matter. Such indigo scarcelyadheres to the tongue, and does not, on being rubbed with the nail, assume acoppery hue. There is met with among the Bengal qualities a variety whichis light blue, yet rather free from extractive vegetable matter, but contains alarge quantity of mineral impurities, and for the rest exhibits pretty muchthe characters of the last-named sort.
The Oude and Coromandel Indigos are generally heavy, brick-shapedmasses, difficult to break, approaching in tinctorial value the medium fineBengal kinds, and are further distinguished into violet and ordinary coppery-looking.