904 INDIGO 



dried. The pieces arc either cubical, or flat and square, or of irregular shape. The 

 quality is very unequal. Java indigo occurs in flat, square, or lozenge-shaped masses, 

 the quality approaching that of Bengal. Both these kinds are consumed chiefly on 

 the continent of Europe. 



Guatemala indigo is imported into this country in serons or hide wrappers, each 

 containing about 150 Ibs. nett. It occurs in small irregular pieces, which are more 

 or less brittle, compact, lighter than water, and of a bright blue colour with an occa- 

 sional tinge of violet. There are three kinds of Guatemala indigo, viz.: 1. Flores, 

 which is the best, and approaches in quality that of the finer Bengal indigos ; 2. 

 Sobres ; and 3. Cortes, which is the lowest in quality, being heavy, difficult to break, 

 and of a coppery-red colour. Of the first kind very little now reaches the market. 

 The indigo of Caraccas is, generally speaking, inferior to that of Guatemala. 



The manufacture of indigo was formerly carried on in St. Domingo, but has for 

 some time been entirely abandoned. 



The indigo of commerce, even when not adulterated, is a mixture of different sub- 

 stances. When it is heated in a state of fine powder to 212 F. it loses from 5 to 10 

 per cent, in weight, the loss consisting of water. When the dry powder is heated in 

 a crucible, a great part of it burns away, and there is left at last a greyish ash, con- 

 sisting of the carbonates and phosphates of lime and magnesia, sulphate of lime, alu- 

 mina, oxide of iron, clay, and sand. These matters are partly derived from the plant, 

 partly from the lime and the imptirities of the water employed in the manufacture. 

 The quantity of inorganic matter contained in ordinary indigo varies very much. In 

 the better qualities it amounts on an average to about 10 per cent, of the weight; 

 whilst in the inferior qualities, especially of Madras indigo, it often rises to between 

 30 and 40 per cent. The organic portion of the indigo, or that which is dissipated 

 when indigo is heated, also consists of several different substances. 



By treating indigo with various solvents, Berzelius obtained, besides indigo-blue, the 

 true colouring matter of indigo, three other bodies, viz. indigo-gluten, indigo-brown, and 

 indigo-red, which seem to be contained in various proportions in all kinds of indigo. 

 Indigo-gluten is obtained by treating indigo with dilute sulphuric, muriatic, or acetic 

 acid, and then with boiling water. It is left on evaporation of its solutions as a yellow 

 transparent extract, which is soluble in spirits of wine, and easily soluble in water, 

 more difficultly in acid liquids. Its taste is like that of extract of meat. It yields by 

 dry distillation much ammonia and a fetid oil, and behaves in most respects like vege- 

 table gluten. On treating the indigo, after being freed from the indigo-gluten, with hot 

 strong caustic lye, the indigo-brown together with a little indigo-blue dissolves, 

 forming a dark brown, almost black solution, from which th.e indigo-brown after fil- 

 tration from the portion insoluble in alkali is precipitated by means of acid. After 

 being purified, indigo-brown has the appearance of a dark brown transparent resin, 

 which is almost tasteless and quite neutral. By dry distillation it affords ammonia and 

 empyreumatic oil. It is decomposed by nitric acid and chlorine. It combines both 

 with acid and bases. Its compounds with alkalis are dark brown, and easily soluble 

 in water. The compound with baryta is not easily soluble in water, and that with 

 lime is insoluble. By boiling the alkaline compounds with lime in excess the indigo- 

 brown may be separated and rendered insoluble. The green substance obtained by 

 Chcvreul from indigo seems to have been a compound of indigo-brown with ammonia 

 containing a little indigo-blue, either in a state of combination or mechanically inter- 

 mingled. Indigo-brown seems to bear a great resemblance in many of its properties to 

 the brown resinous substances obtained by Schunckin the decomposition of indican with 

 acids. From its constant occurrence in all kinds of indigo, it may be inferred that it is 

 not a mere accidental impurity, but stands in some unknown relation to indigo-blue. 

 As long, however, as its origin and composition are unknown, this must remain a mere 

 supposition. After the removal of the indigo-gluten and indigo-brown, the indigo is 

 exhausted with boiling alcohol of specific gravity 0'83. A dark red solution is obtained, 

 which is filtered and distilled, when the indigo-red contained in it is deposited as a 

 blackish-brown powder, which is quite insoluble both in water and in alkaline liquids. 

 Indigo-rod, according to Berzelius, is amorphous, but by distillation in vacuo yields ;i 

 white crystalline sublimate, as well as unchanged indigo-red. Concentrated sulphuric 

 acid dissolves it, forming a dark yellow solution, which deposits nothing on being mixed 

 with water ; the diluted solution is rendered colourless by wool, which at the same time 

 acquires a dirty yellowish-brown or red colour. The description given by Berzelius 

 leaves it doubtful whether the indigo-red obtained by him from indigo was a pure 

 unmixed substance. From the leaves of the indigoferae, as well as from those of the 

 It>af.i$ tinctoria, a substance may, aeeoniinL' ;<> S.-hunck, be extracted which has re- 

 re:ved from him tho name of indirubinc, but which seems to be merely indigo-rod in a 

 state of purity. This substance has, according !> Sclmnck, the following properties : 

 it crystallises in small silky needles of a brownish-purple colour, which when rubbed 



