INDIGO 899 



rain, the indigo-producing principle diminishes very considerably, and sometimes 

 even disappears entirely, so that, if cut during- or immediately after rain, the plants 

 yield little or no indigo. The indigo-plant is subject to the attack of a green cater- 

 pillar, which sometimes appears in such quantities as to destroy the whole crop. No 

 certain and easy means of destroying this pest is known. It has been recommended 

 to pass wooden rollers over the ground, before the plants have attained any great 

 size, so as to crush the caterpillars without injuring the plants, and this plan has been 

 attended with partial success. 



In order to obtain good results in the manufacture of indigo, it is necessary that 

 the plants should be of the same age, of the same species, and from the same field. 

 The Indigofcra Anil begins to ferment several hours sooner than the /. tinctoria, so 

 that if a mixture of both be taken, the produce from either one or the other will be 

 lost, and the indigo obtained will also be of a bad quality. The plants should, as 

 soon as possible after being gathered, be placed in the steeping-vat, which is a vessel 

 built of bricks, and well lined with cement, from 3 to 8 meters in length, of the 

 same width, and about 1 meter deep. In this vessel the plants are arranged in suc- 

 cessive layers, the lower layers being slightly inclined towards one end, in order to 

 facilitate the subsequent running-off of the liquor. The vessel being full, a number 

 of poles of fir-wood are laid lengthways over the plants, at a distance of 162 mill, 

 from one another. Three beams are then laid crosswise over the poles, their ends 

 being well secured by passing them through slits which are cut in the upright 

 posts at the sides of the cistern, and then fixing them by means of iron pins, passing 

 through holes in the posts. By this means the plants are prevented from rising 

 above the surface of the liquor during the process of maceration. The vat is now 

 filled with water from an adjacent cistern, in which it has been allowed to stand 

 for 24 hours for the purpose of allowing all foreign matters contained in it to be 

 deposited. After standing in contact with the leaves for about 6 hours, a change 

 usually begins to manifest itself in the liquor, which must therefore, from that time 

 forward, be carefully watched. As soon as this liquor begins to acquire a green 

 colour, and when a little of it, on being kept for a short time in the mouth, leaves a 

 slight impression of harshness (aprete) on the tongue and the palate, it is a sign that 

 the maceration is complete, and that the liquor should be drawn off without delay. 

 If this be not done, the colour of the liquor changes from green to brown, a new 

 species of fermentation commences, accompanied by the formation of acetic acid, and 

 the plant begins to yield substances of a mucilaginous nature, which contaminate the 

 indigo, and completely spoil its quality. It is therefore of the greatest importance 

 to ascertain exactly when the maceration of the plant is complete. The following 

 are the chief indications of this point having been attained : 1. When the water 

 \vhich was at first clear begins to become muddy, and acquires a slight greenish tinge. 

 2. When bubbles of a greenish colour rise to the surface here and there. 3. When 

 towards the edge of the vat some mucilage, or a kind of greyish scum, commences to 

 be formed. 4. When a very slight purple pellicle is observed on the surface of the 

 liquor, especially near the corners of the vat. 5. When the liquor begins to exhale a 

 slight but not disagreeable odour of herbs. When the fermentation has proceeded too 

 far, the following phenomena present themselves: 1. A considerable quantity of 

 large bubbles of air are disengaged, which burst at the surface, forming a layer of 

 greyish mucilage. 2. The surface of the liquor becomes covered with a copper- 

 coloured pellicle. 3. A heaving of the liquor in the vat is observed, giving rise to 

 the disengagement of large greenish bubbles, which communicate a brownish colour 

 to the water. 4. The liquor acquires a fetid smell, a strongly acid taste, and a soapy 

 appearance. These phenomena manifest themselves when the weather is hot, after 

 the fermentation has continued about 12 or 14 hours. It then becomes impossible 

 to obtain indigo of good quality, the only product being a black matter resembling 

 wax. 



The liquor is now run off from the steeping-vat into the beater, which is a cistern 

 of about the same dimensions as the former, but situated at a rather lower level. Here 

 it is subjected to the beating process, the object of which is to expose the reduced 

 indigo to the oxygen of the atmosphere, as well as to promote the disengagement of 

 the carbonic acid gas with which the liquid is charged, and which prevents the pre- 

 cipitation of the indigo. The beating is performed by men, who, provided with 

 paddles, agitate the liquid rapidly, so as to bring every part of it successively into 

 contact with the air. It is of importance that this process should be broken off at the 

 right moment, for if it be continued too long, the grain formed at first will redissolve 

 and be lost. And if, on the other hand, it be arrested before the proper time has 

 arrived, a portion of the indigo will remain unprecipitated. In order to ascertain in 

 what state the liquor is, a little of it must be poured into a drinking glass and mixed 

 with an equal volume of clear water. If there is formed round the circumference of 



