1ND 



IND 





cients procured it from the East Indies ; 

 in modern times it has been transplanted 

 into America. The cultivation of it, suc- 

 cessively attempted at different places, 

 appears to be fixed at Carolina, St. Do- 

 mingo, and Mexico. That which is 

 known under the name of Guatimala in- 

 digo, from whence it comes, is the most 

 perfect of all. 



Indigo may be obtained from the me- 

 rium tinctorium, and the isatis tinctoria 

 or woad; a plant cultivated and even 

 found wild in England. When arrived 

 at maturity, this plant is cut down, wash- 

 ed, dried hastily in the sun, ground in a 

 mill, placed in heaps, and allowed to fer- 

 ment for a fortnight. It is then well mix- 

 ed, and made up into balls, which are 

 piled upon each other, and exposed to 

 the wind and sun. In this state they be- 

 come hot, and exhale a putrid ammonia- 

 cal smell. The fermentation is promoted, 

 if necessary, by sprinkling the balls with 

 water. When it has continued for a suf- 

 ficient time, the woad is allowed to fall 

 to a coarse powder ; in which state it is 

 sold as a dye-stuff. By treating woad 

 ,nearly in the same manner with the indi- 

 gofera, indigo has been obtained from it 

 by different chemists. 



Indigo is a soft powder of a deep blue, 

 without either taste or smell. It under- 

 goes no change, though kept exposed to 

 the air. Water, unless kept long upon it, 

 does not dissolve any part of it, nor pro- 

 duce any change. When heat is applied 

 to indigo, it emits a bluish red smoke, 

 and at last burns away with a very faint 

 white flame, leaving behind it the earthy 

 parts in the state of ashes. Neither oxy- 

 gen nor the simple combustibles have any 

 effect upon indigo, except it is in a state 

 of solution; and the same remark applies 

 to the metallic bodies. The fixed ^alka- 

 line solutions have no action on indigo, 

 except it is newly precipitated from a 

 state of solution. In that case, they dis- 

 solve it with facility. The solution has 

 at first a green colour, which gradually 

 disappears, and the natural colour of the 

 indigo cannot be again restored. Hence 

 we see that the alkalies, when concen- 

 trated, decompose indigo. Pure liquid 

 ammonia acts in the same way. Even 

 carbonate of ammonia dissolves precipi- 

 tated indigo, and destroys its colour ; but 

 the fixed alkaline carbonates have no 

 such effect. Lime-water has scarcely 

 any effect upon indigo in its tfimal state ; 

 bwt it readily dissolves precipitated indi- 

 go. The solution is at first green, but 

 becomes gradually yellow, When the 



solution is exposed to the air, a slight 

 green colour returns, as happens to the 

 solution of indigo in ammonia, but it 

 soon disappears. 



The action of the acids upon indigo 

 has been examined with most attention ; 

 it certainly exhibits the most important 

 phenomena. When diluted sulphuric 

 acid is digested over indigo, it produces 

 no effect, except that of dissolving the 

 impurities; but concentrated sulphuric 

 acid dissolves it readily. One part of 

 indigo, when mixed with eight parts of 

 sulphuric acid, evolves heat, and is dis- 

 solved in about twenty-four hours. Ac- 

 cording to Haussman, some sulphurous 

 acid and hydrogen gas are evolved during 

 the solution. If so, we are to ascribe 

 them to the mucilage and resin which are 

 doubtless destroyed by the action of the 

 concentrated acid. 



The solution of indigo is well known in. 

 this country by the name of liquid blue, 

 or sulphate of indigo. While concen- 

 trated it is opaque and black : but when 

 diluted it assumes a fine deep blue co- 

 lour ; and its intensity is such, that a sin- 

 gle drop of the concentrated sulphate is 

 sufficient to give a blue colour to many 

 pounds of water. Bergman ascertained 

 the effect of different re-agents on this 

 solution with great precision. Drop! into 

 sulphurous acid, the colour was at first 

 blue, then green, and very speedily de- 

 stroyed. In vinegar it becomes green, 

 and in a few weeks the colour disap- 

 pears. In weak potash it becomes green, 

 and then colourless. In weak carbonate 

 of potash, there are the same changes, 

 but more slowly. In ammonia, and its 

 carbonate, the colour becomes green, and 

 then disappears. In a solution of sug-ar, 

 it became green, and at last yellowish. 

 In sulphate of iron, the colour became 

 green, and in three weeks disappeared. 

 In the sulphurets the colour vr as destroy- 

 ed in a few hours Realgar, white oxide 

 of arsenic, and orpimcnt, produced no 

 change. Black oxide of manganese de- 

 stroyed the colour completely. From 

 these and many other experiments it was 

 inferred, that all those substances which 

 have a very strong affinity for oxygen 

 give a green colour to indigo, and at last 

 destroy it. Hence it is imagined, that 

 indigo becomes green, fey giving out oxy- 

 gen. Of course it owes its blue colour 

 to that principle. 



IND1GOFERA, Indigo, or Indicum> in 

 botany, a genus of the Diadelphta Decan- 

 dria class and order. Natural order of 

 PapUionaceie, or Leguminos*. Essential 



