Vol. XIII. No. 331. 



THE AGKICULTURAL NEWS. 





INDIGO. 



Thi_' productioo of the dye indig ><n some of the many 



of the genus [ndigofera has been carried on in India 

 from very earlj times. ~<" profitable was it that in the latter 

 part of the 17th, and first half of the 18th centuries it 

 was widely undertaken in the Wesl Indies, the West [ndian 

 species ( /. Anil) yielding a dye hardly inferior to that 

 obtained from India. Owing however to the superior profits 

 • 1 from sugar-cane cultivation, the cultivation of 



indigo was practically abandt I in the Wesl Indies about 



the middle of the 1 8th century, and has never been rei 



also its cultivation in India has been very 

 much id, owing to the manufacture, ehiefh in 



Germany, of the synthetic article, which could be produced 



cost lower than that at which it was profitable to place 

 the natural article on the market. 



On arc, mit of the war the supply of this synthetic 

 article is likelj to be verj short. Inquiries have been made 

 from th«-' Imperial Department of Agriculture whether it 

 would be likeU to be profitable to re ascitate the cultivation 



and manufacture of indigo in son f these islands at the 



present time. It must be borne in mind that on account 

 of their ancient acquaintance with the process, the Indian 

 growers can easily at once increase the output of natural 



ich an extent as to handicap very heavily experi- 



il attempts in this direction in other parts of the world. 



a, the manufacture of the synthetic product, long left 

 a German monopoly, can easily be undertaken, if found 

 to be profitable, by the great manufacturing chemists in 

 Great Britain and ether countries. In fact, as has been 

 noticed in a gleaning on page L2 of this issue of the Agricul- 

 tural News, the Imperial Governmentjjias already expressed 

 its willingness toaid in the establishment of such manufacture. 

 Still as enquiries have been made on this point, some account 

 if the cultivation and manufacture of indigo will be of 

 interest. 



It has been found in India that Indigofera arrecta, 



tes from Java or Natal, yields a larger pei , M i ,_, 



of indigotin, than the more widely cultivated species, 



/. tumatrana, known less correctly as /. tinctoria. The 



• /. Anil, wild or naturalized throughout the West 



Indies, is not considered to 1 1 equal value with either of 



the other two species. 



The cultivation of indigo is apparently not very difficult; 

 the crop matures, under varying conditions of climate, at 

 from six to eighteen months. The dye is obtained from the 

 stalks and leaves of the plant, which are cut when the plant 

 IS about 3 feet high. It may be remarked that, like 



other Leguminosae, indigo is a very valuable rotation crop, 

 and the waste product, after the extraction of the dye, is 



highly prized as a manure. 



The following is hi abstract from Sir George Watt's 

 Commercial Products of India, on the manufacture of indigo. 



For the manufacture of dye from the plant the wet 



is ion almost invariably adopted. It is essential to 



have an abundant supply of water, ts the process consists in 



extraction of the dye-yielding principle from the plant by 



steeping in water, and the precipitation, from the extract o 



indigo, lo exposun to air ox idat ti m. At 



point of t oi placed a large tank, 



from which watei can be run to th its. These 



area row of cement lined brick basins, usually about 20 feet 

 quare md I to 5 feet di ep. Bel >w I hese there is a 

 the s, Dumber of slightlj shallower 'beating' vats. 



The plant is taken from the field md loaded into the 

 teeping vats. \ i is full, I : ents are 



bal tened down bj beam ittai hed to pegs set b 

 the vat, and water is nm into it until the plant is just 

 submerged. Steeping is allowed to proceed for from twelve 

 to fourteen hours, 1>.\ whii h time the liquor i» lowish 



green; it is then run off into the lower or beating vat. 



The object of bea tng is to obtain as thorough an 

 oxidation as possible. The more primiti id is for ten 



or i welve coolies to entei the ?at, I he liquor with 



short sticks, to one end of which a Hat disc of wood is 

 ittached. The process is considered con 

 a hall hours continuous beating. This hand-b i been 



largely replaced by wheel-beating, operated b} machinery. 

 Where this is employed, there is one beating vat, running 

 the length of the range of sti ping ■ d along its 



length l>\ one or two walls, according to whether • or 



two wheels are employed. These walls stop short of the 

 two ends of the mii, and are merelj to give direction 

 to the current set up l>\ the wl I. The wheels i sisf of 



flat discs of wood attached to the ends of the spokes radiat- 

 ing from the axle. Heating 1>\ this method is completed in 

 about an hour. Beating has been replaced in some modern 

 factories by blowing a mixture of air and steam through the 

 liquor, and, later still, by blowing ammonia through it. 

 Neither of these, howe\er, has I ieen generally adopted. 



After beating is complete, the liquor is allowed to stand 

 until the precipitated indigo has settled to the bottom of tic- 

 tank, leaving a clear red liquor above. This is drained off, 

 and the residual precipi iti is pumped into boilers, where 

 having been mixed with clean water it is boiled either by 

 steam or direct heat. When the boiling is complete, the 

 contents of the boiler are run on to a 'table'. This consists 



of a heavy canvas sheet, wetted and spread on a w len 



support. This acts as a filter, allowing the water to drain 

 oft', and retaining the indigo as a thick paste. This paste. 

 is then transferred to the press, which is a strong square 

 wooden box, with perforated bottom and sides. The interior 

 of the press is lined with damp cloth, and the wet paste is 

 poured into it to a depth of 8 or 9 inches. The lid, which 

 tits the interior accurately, is then screwed home by means 

 of a screw worked bj a long lever. This is turned at 

 intervals during five or six hours, by which time the paste will 

 have been pressed into a hard cake 3 or .'!.', inches thick. 

 This is then removed to a table, where it is cm by win- into 

 cubes of about 3 inches. These are placed to dry on shelves 

 in an airy room. During the process of drying, the cakes 

 become covered with alayerof mould, which is brushed off 

 before packing. The dried ami cleaned cakes are then 

 packed into specially constructed cases, weighed and shipp id. 



In Ceylon in the last few years there has been same 

 interest in the cultivation and manufacture of indigo. It. 

 is claimed that much advantage accrues from the plan 

 adopted there, of employing a process which enables the 

 manufacturer to place his indigo upon the market, not as 



dried squares, bul as a paste, thus avoiding the necessity of 



much grinding and mixing by the dyers in re, verting 



tin- indigo to paste, in which form it is used by them. This 

 past,- is exported in lead-lined boxes. 



Ii will lie seen from the above that to undertake the 



manufacture of indigo would require i In laj of , i in <i, lei , 



ble capital in the construction of a factory, 

 technical acquaintam i 'ess. 



