900 INDIGO 



the glass a line of a bluish-green colour, tho beating must be continued ; but if, on the 

 contrary, the liquid appears of a uniform brown colour, .and if on adding to it a few- 

 drops of clear lime-water with the finger the indigo precipitates immediately in grains, 

 tho process must be arrested. The beating usually occupies from an hour and a half 

 to two hours. The liquid is now to bo well mixed with about ^th of its volume of 

 clear lime-water, and allowed to rest until the indigo has quite settled. By opening 

 successively the plugs which are placed at different heights in tho side of the vessel, 

 the clear liquor is then drawn off in separate portions and permitted to run away, care 

 being taken that none of the indigo is allowed to be carried away with the water. 

 By means of an opening^ situated near the bottom of the beating vat the indigo mixed 

 with water is then run off, and flowing through a canal is received on a cloth strainer 

 or filter. This filter rests on a round or four-cornered vessel, the top of which is on 

 a level with tho surface of the ground, and which is called tho diablotin. When tho 

 liquid has run through the filter, the indigo which remains behind in a state of paste 

 is mixed up again with water, and the mixture is poured on a canvas filter and 

 allowed to run immediately into the boiler. The refuse matter, consisting of leaves of 

 tho plant, &c., remains on the canvas, while the indigo suspended in water runs 

 through. The boiler is a vessel with sides of masonry, and a bottom consisting of a 

 copper plate which rests on iron bars, and is well cemented to the sides. Underneath 

 the copper plate is the fire-place. The top must be covered with a wooden lid, con- 

 sisting of two flaps which are fixed to hinges at the sides and meet together over tho 

 top. At the moment when the mixture of indigo and water is introduced into the 

 boiler, the latter must already be about one third full of hot water, tho mixture being 

 sufficient almost to fill it entirely. The heat is now raised gradually to the boiling- 

 point, and the boiling is continued for about two hours. In order to prevent the indigo 

 from adhering to the bottom and sides of the boiler, the liquor must be kept continually 

 stirred with a wooden rake. The object of the boiling is to drive away all the carbonic 

 acid that may still be present in the liquor, to remove the soluble extractive matters 

 which would render the indigo dull and impure, to prevent the fermentation or putre- 

 faction of the indigo which would otherwise take place, and lastly, to facilitate tho 

 subsequent processes of filtering and pressing. The fire having been removed, tho 

 liquor is allowed to stand for some time, and as soon as the indigo has settled, tho 

 supernatant liquid is drawn off by means of taps fixed in one of the sides of the 

 boiler. The lowest tap is then opened, and the indigo is run off with the water and 

 received on a filter, consisting of blue Guinea cloth stretched on a frame. Tho first 

 portions of liquid which run through are usually coloured with indigo, and must 

 therefore be caught in a suitable vessel and poured on the filter again. As soon as 

 the liquid has percolated, the indigo, which is now a compact paste, is removed from 

 the filter by means of a wooden ladle and put into a press, which consists of a wooden 

 box pierced with holes. The press having been lined with cloth, the indigo is put in, 

 the cloth is folded round it as evenly as possible, a wooden lid is dropped on the 

 cloth, and the mass is submitted to pressure by means of a screw, until no more liquid 

 runs through at the bottom, which takes place as soon as the indigo has been reduced 

 to about a third of its original volume. The press is then opened, tho indigo is taken 

 out of the cloth, laid on a table and divided by means of a knife into pieces of a cubical 

 shape. These cubes are then taken to the drying shed, where they are placv>l on 

 trellises covered with matting or very thin cloth, so as to admit of the free pass; 1 1:1- of 

 air. Care must be taken not to dry them too rapidly, otherwise the cakes would 

 crack and split into fragments, which are then of little commercial value, and it is 

 therefore necessary to protect them from currents of dry air by covering them with 

 canvas or Guinea cloth. During the drying process, which occupies from 8 to 10 

 days, the cakes should be turned several times. They are then closely packet I in 

 boxes, each box holding about 25 kilogrammes. The boxes should be lined with paper. 

 It maybe remarked, that when the indigo is of good quality, the volume of the paste 

 diminishes very little when subjected to pressure. If the process of filtering takes up 

 much time and the pressing is attended with difficulty, it may bo anticipated that tho 

 indigo will turn out of bad quality. This may proceed from tho plant having been 

 overgrown, or from the maceration or the beating process having been continu 

 long, or from the employment of too largo A quantity of lime-water. The difficulty 

 experienced in pressing the indigo paste, and which is often so great as to cause the 

 cloth in which it is enveloped to break, is caused by tho presence of a mucilaginous or 

 viscous substance mixed with the indigo, which may bo removed by treating the pasto 

 again with boiling water, and repeating tho operations of filtering and pressing. 

 In regard to the state in which indigo exists in the plants from which it is (! 

 and the nature of the process by which it is obtained, various opinions have been 

 entertained by chemists. Berthollet in his work on dyeing says, ' that the three parts 

 of the process employed have each a different object. In the first a fermentation is 



