INDIGO S95 1 



dark brown tint, a viscid appearance, an unpleasant smell, and a bitter taste. It 

 becomes moist in damp air, and dissolves in water without decomposition. It is 

 precipitated by lime, alkalis, infusion of galls, and acetate of lead. All indigo con- 

 tains a little lime derived from the plant, even though none has been used in its pre- 

 paration. 



2. Indigo from dried leaves. The ripe plant being cropped, is to be dried in sunshine 

 from 9 o'clock in the morning till 4 in the afternoon, during two days, and threshed 

 to separate the stems from the leaves, which are then stored up in magazines until a 

 sufficient quantity is collected for manufacturing operations. The newly-dried leaves 

 must be free from spots, and friable between the fingers. When kept dry, the leaves 

 undergo, in the course of four weeks, a material change, their beautiful green tint 

 turning into a pale bluish-grey, previous to which the leaves afford no indigo by 

 maceration in water, but subsequently a large quantity. Afterwards the product 

 becomes less considerable. 



According to some manufacturers, the plants should be cut down in dry weather, 

 an hour or two before sunset, carried off the field in bundles, and immediately spread 

 upon a dry floor. Next morning the reaping is resumed for an hour and a half, 

 before the sun acts too powerfully upon vegetation, and the plants are treated in the 

 same way. Both cuttings become sufficiently dry by 3 o'clock in the afternoon, so as 

 to permit the leaves to be separated from the stems by threshing. They are now 

 thoroughly dried in the sunshine, then coarsely bruised, or sometimes ground to powder 

 in a mill, and packed up for the operations of manufacture. 



The following process is pursued to extract indigo from the dried leaves. They 

 are infused in the steeping vat with six times their bulk of water, and allowed to 

 macerate for two hours with continual stirring till all the floating leaves sink. The 

 fine green liquor is then drawn off into the beating vat, for if it stood longer in the 

 steeper, some of the indigo would settle among the leaves and be lost. Hot water, 

 as employed by some manufacturers, is not necessary. The process with dry leaves 

 possesses this advantage, that a provision of the plant may be made at the most 

 suitable times, independently of the vicissitudes of the weather, and the indigo 

 may be uniformly made ; and moreover, the fermentation of the fresh leaves, often 

 capricious in its course, is superseded by a much shorter period of simple macera- 

 tion. 



"We are indebted to Dr. Roxburgh, for a description of the method employed for 

 manufacturing indigo from the Ncrium tinctorium or Wrightia tinctoria. (Vide ' Trans- 

 actions of the Society of Arts,' vol. xxviii.) This plant, which attains the size of a 

 small tree, is found on the lower regions of the mountainous tract near Rajamundry, 

 and also on hills in the neighbourhood of Salem and Pondicherry, and grows in a 

 sterile as well as rich soil. The leaves begin to appear in March and April, and 

 at the end of April have attained their full size, when they are ready for gathering. 

 At the end of August they begin to assume a yellowish rusty colour and soon fall 

 off. The leaves yield no indigo until the plant is several years old, but the best 

 leaves for making indigo are obtained from low bushy plants. They improve when 

 kept for a day or two, but when they begin to wither, they yield but a small portion 

 of very bad indigo, and when quite dry only a dirty brown fecula. In this they 

 differ from the leaves of the common indigo-plant, which may be dried before ex- 

 traction without loss of colour. They also differ from the latter in not yielding their 

 colour to cold water. With cold water only a hard, black, flinty substance is ob- 

 tained, not blue indigo. It is therefore necessary to employ hot water, which ex- 

 tracts the colour very readily. The leaves having been collected, are on the ensuing 

 day thrown into copper scalding vessels, which are then filled with cold water to 

 within 2 or 3 inches of the top. Hard water containing a large quantity of bicarbonate 

 of lime is better adapted for the purpose than rain-water. The fire is then lighted 

 and maintained rather briskly until the liquor acquires a deep green colour. The 

 leaves then begin to assume a yellowish colour, the heat of the liquor being about 

 150 to 160 Fahr. The fire is then removed, and the liquor run off into the beating 

 vat. Here it is agitated from 5 to 20 minutes. It is then mixed with about ^th to ^th 

 part of lime-water, which produces a speedy granulation. After the indigo has subsided, 

 the supernatant liquid appears of a clear Madeira wine colour. The quantity of indigo 

 obtained, amounts to 1 Ib. from 250 Ibs. of green leaves ; but it varies according to the 

 season and the state of the weather. In August and September, the produce is only 

 one-half or two-thirds of what it is in May and June, and even that is diminished if 

 the weather is wet, or the leaves are treated immediately after being gathered. The 

 scalding requires about three hours, and the agitation and precipitation the same 

 time. The indigo is improved by treating it with a little sulphuric acid. The only 

 fault it has is, that it breaks into small pieces, unless it has been dried slowly in the 

 shade protected from the sun. 



