INDIGO. 



505 



it completely. Sulphuric acid dissolves it, and 

 causes it to acquire a more lively, though a less 

 durable colour than it naturally possesses. This 

 peculiarity has been taken advantage of by the 

 dyers, and sulphate of indigo, under the name 

 of Saxon blue, is a well known ingredient of 

 the dye-house. Its application was first discov- 

 ered and carried on in Saxony in the year 1740, 

 whence its name. That powerful chemical 

 agent, chlorine, instantly decomposes indigo. 



This valuable dye has a strong affinity for 

 almost every species of fibrous texture, whether 

 animal or vegetable; it can therefore impart to 

 all descriptions of stuff a very permanent colour, 

 without the assistance of a mordant. By the 

 superiority and richness of its dye, the facility 

 with which it is worked, and the other advan- 

 tages attending its employment, indigo has nearly 

 superseded the European woad as a first colour; 

 woad being now rarely used except as an auxil- 

 iary. Indigo can only be applied as a dye in a 

 state of solution, and must consequently be 

 deprived of its oxygen, to be rendered again 

 soluble in water. Ingredients therefore, having 

 a strong affinity for oxygen, are mixed in the 

 vat together with the indigo, whereby it is again 

 held in a state of solution. To produce this 

 effect, the dyers usually employ protoxide of 

 iron, to deoxidize it, and lime water to render 

 it soluble in its yellow green state. Bancroft 

 considers that its colouring matter is somewhat 

 injured by this process, and supposes that the 

 very durable blue dyes of some nations, in 

 different parts of Asia and Africa, are derived 

 from the indigo plant employed when the colour 

 is first extracted by steeping and fermentation. 

 The Chinese are said thus to apply this dye, and 

 the Africans use it in a way nearly similar. Mr 

 Clarkson has remarked that the dyes of Africa 

 are superior to those of any other part of the 

 globe. The blue produced there is so much 

 more beautiful and permanent' than that which 

 is extracted from the same plant in other coun- 

 tries, that many have been led to doubt whether 

 the African cloths brought into this country 

 were dyed with indigo. It was believed that 

 this vivid and permanent African colour, which 

 obtained more lustre by repeated washings, must 

 have been derived from some other plant, or 

 extracted from some of the woods of the country 

 celebrated for imparting beautiful colours. It 

 has, however, been clearly ascertained, that the 

 balls of indigo, prepared by the Africans, are 

 simply the leaves rolled up. Two or three of 

 these balls have been procured, and subjected to 

 chemical examination. 



M. Adanson, in noticing the indigo cultivated 

 by the negroes in Senegal, observes that these 

 people do not take much trouble to draw the 

 dye out of the plant. The leaves are gathered 

 at any time in the year, and merely pounded in 



a mortar tiU reduced to a paste. This paste is 

 made up into leaves in order to be preserved dry. 

 When required for use it is dissolved in a kind 

 of ley, made of the ashes of an unctuous plant 

 which grows in the fields, and is called by the 

 natives rhemi, — in this, the cloth to be dyed is 

 immersed. It is supposed that indigo in this 

 state, will keep as long as that which has received 

 the usual preparation; but the enhanced expense 

 of freight caused by the much greater bulk of 

 the article thus simply prepared, is perhaps a 

 sufficient objection to its importation in that 

 form. 



Indigo is imported into England at a duty of 

 threepence per pound for that grown in British 

 possessions; the addition of another penny per 

 pound is placed on that coming from foreign 

 ports. 



The average quantity of this substance annu- 

 ally imported, for the last five years, is 27,342 

 chests of East Indian, weighing from 2 to 3 

 cwt. each; and 3,161 serons, Spanish, weighing 

 about 250 lbs. each; a considerable portion of 

 which is re-exported to the continent of Europe. 



Another species of indigo was discovered by 

 Dr Roxburgh, to which he gave the name of 

 ccBrulea, from the beauty of its colour. It is an 

 erect shrubby species, growing naturally in some 

 parts of India, on dry, barren, uncultivated 

 grounds, to the height of from one to three feet, 

 and still higher in a better soil. It mainly 

 resembles the indigofera argentea, somewhat 

 differing from that plant in the shape and gi-owtli 

 of its leaves. A much finer indigo of a lightei 

 colour was obtained from it, and in a larger pro- 

 portion, than from the common plant. Eight 

 pounds of these leaves gave two hundred and 

 forty grains of indigo. Another species of indigo, 

 called by Thunberg the indigofera arborca, was 

 cultivated by the Dutch colonists at the Cape of 

 Good Hope. 



In the year 1792 Dr Roxburgh transmitted 

 home a sample of indigo prepared from the leaves 

 of a species of rose bay, which he distinguishes 

 by the name of neritem tinctorium. From the 

 excellent quality of this indigo, and other advan- 

 tages attending its cultivation and preparation, 

 it might have been supposed that the neriiim 

 indigo would quickly have become an article of 

 commerce, and have been in much request among 

 our dye-houses; but it has not yet taken its place 

 among the imported eastern productions, though 

 it should seem that the extensive cultivation of 

 this tree would be attended with much less 

 labour and cost, and offer a gi'eater certainty of 

 profit than the common indigo plant. 



The neriwm grows plentifully throughout the 

 Carnatic, and in every part of the Circars where 

 there are hiUs and mountains, being an extent 

 of about a thousand miles in length. Near 

 inhabited places it is so often cut down for fire 



