INDIGO. 



shrubby, /. disperma, yielding a supe- 

 rior dye, is cultivated. L're, also, 

 states that the /. pscudo linctoria of 

 the East Indies furnishes the best in- 

 digo. The most successful culture of 

 these plants is near the tropics, where 

 the mean temperature reaches 75° 

 and 80" Fahrenheit ; but species of 

 indigofera grow to the north of tliis 

 position. The soil should he light 

 and rich; the seeds are sown in April 

 in drills, run at distances from 15 to 

 20 inches apart ; they require moist- 

 ure, but should not be planted in an 

 undrained soil. Twelve pounds of 

 seed answer fur the acre. The young 

 plants are to be kept free from weeds, 

 thinned, and hoed up. The plants 

 are cut with a reaping-hook near the 

 earth, when about to flower, or as 

 soon as the lowest leaves begin to 

 turn : this period will be in July in 

 South Carolina. A second crop is 

 taken at the end of August, and a 

 third crop in Guatimala and India. 

 The root stems also yield good indi- 

 go a second year in rich soils, but 

 one year is usually the term for suc- 

 cessful cultivation. The first crop is 

 the best. The excellence of the in- 

 digo will depend upon the brightness 

 of the season ; long-continued wet 

 weather produces large plants, but a 

 smaller quantity of die. 



Preparation of Fresh Leaves. — The 

 harvested plants are at once carried 

 to a vat or steeping-tank of wood or 

 masonry ; here they are immersed in 

 water, being kept imder by weighted 

 boards ; fermentation soon begins, 

 and is allowed to continue about 18 

 hours, during which the colouring 

 matter is extracted from the leaves. 

 The fermenting vat is some 20 feet 

 square, and two to three feet deep, 

 and the bottom set on a level with 

 the top of a second or mashing-tank. 

 As soon as the scum produced in fer- 

 mentation begins to subside, the li- 

 quid should be allowed to flow into 

 the lower vessel. The decanted fluid 

 is of a yellowish tinge ; when in the 

 mashing vessel, it is to be violently 

 beaten with paddles or other means 

 for an hour or more, when the blue 

 begins to form in flocks and precipi- 



tate. At first there is much froth, 

 but this subsides as soon as the Hocks 

 become granulated ; the beating is 

 stopped when the granulations occur, 

 and the fluid begins to clear if allowed 

 to stand. If the fermentation has 

 been defective, the froth is very abun- 

 dant, and must be allayed by pouring 

 oil over the surface ; if over-ferment- 

 ed, a thick fatty crust covers the li- 

 quid, which does not disappear on in- 

 troducing oil. In this case the beat- 

 ing or cliurning is to be moderated. 

 The indigo precipitates during 20 

 hours, leaving the water transparent 

 and free from froth. Tiie surface 

 water is now to be drained off by 

 stop-cocks or plugs in the side of the 

 vessel. In Central America, the thick 

 semifluid mass of indigo is scraped 

 up and placed on a stout cloth, to 

 drain and dry in the sun, and after- 

 ward cut into small pieces for the 

 market. Stove-drying is equally ef- 

 fective. When dried, any white ef- 

 florescence that appears should be 

 wiped off. Liraewater is sometimes 

 used to assist the precipitation of the 

 indigo ; but it is not advisable, as the 

 colour is injured. 



Preparation of Dried Leaves. — In 

 India the plants are sometimes care- 

 fully dried in the sun, the leaves 

 thrashed from the stems, and stored 

 in barns until enough is accumulated 

 for sale or manufacture. The leaves 

 change, in four or more months, from 

 green to a blue gray in the mass, and 

 then become ready for use. They are 

 placed in the steeping-vat with six 

 times their weight of water, and con- 

 tinually stirred for two hours or more, 

 until the floating leaves sink. The 

 solution is now green, and to be im- 

 mediately run oft" into the mashing- 

 vat, where it is treated as before. 

 There is no fermentation in this pro- 

 cess. Limewater is sometimes used 

 to hasten the granulation, but is not 

 necessary, except in the case of plants 

 which yield little colour, as woad 

 (Isatis tinctoria). 



In some cases the leaves are pound- 

 ed ; the solution is then strained be- 

 fore beating. 



The product of indigo in South 



417 



