I N D 



117 



I N D 



Indie* takes place ; and, after it has settled a little, he evo- 

 ~ ""*' lution of carbonic acid wholly cease*. When the pre- 

 cipitation is complete, the supernatant liquor is of a 

 clear brandy or Madeira wine colour. A greenish or 

 olive tint is an evidence of imperfect precipitation, and 

 arises either from its being united to a portion of car- 

 bonic acid, or its nut having absorbed a sufficiency of 

 oxygen, most probably the latter, as a further exposure 

 to the atmosphere by churning causes it to precipitate 

 an additional portion of indigo when treated with al- 

 kalies. 



Great attention must be paid, in all the stages of this 

 process, to adjust the best degree of each change. If 

 the fermentation is too soon stopped, a part of the indi- 

 go remains nnextracted. This is ascertained by the 

 colour of the twigs, when a few are taken out and in- 

 spected. They are of a pale yellow, and tender, when 

 they hare yielded the whole. The degree of evolution 

 of gas is also to be regulated : when the quantity is de- 

 ficient, the liquor h of a yellowish green. When the 

 fermentation is carried too far, the liquor becomes tur- 

 bid, from an admixture of grosser parts separated from 

 the plant, and the condensation and precipitation of the 

 indigo are prevented from taking place with the due 

 v, and from yielding an article of genuine purity. 

 This is more dangerous than a deficient fermentation, 

 as not being so easily remedied. It appears from the 

 experiments of Dr. Roxburgh, that the abtorpt 

 oxygen is essential both during the fermentation and 

 the precipitation. 



The only farther pro.-esf which the indigo under- 

 goes, is that of drying, which sometimes is effected 

 solely by dripping ; at other times it is subjected to a 

 pressure, by which the water is squeezed out. It is 

 exposed to a free current of air, but haded from the 

 light of the sun. 



Indigo differs gre.v excellence, as well M in 



it* accidental properties. Some specimens of it hare 

 much less specific gravity than others, and the lightest 

 is the purest. Some of it * ill even float in wat< 

 the air ii excluded while it it in any degree moist, it 

 undergoes a chemical change, by which white specks 

 are formed in hs substance. When too much lime has 

 been used in precipitation, it subsides mixed with th 

 indigo, and throws down other adulterating matters. 

 Indigo differ* greatly in colour. < >f the (iuatimala in- 

 digo, the most esteemed sort which ecmes from Ame- 

 rica, there are three yarieties ; one called > /Cora, has 

 fine blue colour ; a second, called oeW tttltrnte, is vio- 

 lrt ; and the third, called corti-color, ii copper coloured. 

 the fir- 1 sell* at 9s. per lib., the second is 7. and 

 the third 5. bd. Of the East Indian indigo, the Ja- 

 vanese WM formerly preferred to all others ; but the 

 manufacturr b now cultivated to a considerable extent 

 in the Hriti.h possessions, and an article U produced 

 which U often superior even to that of ( iuitmula. 



The comparative value- of indigo may be ascertained 

 by dissolving equal portrom uf different specimens in 

 sul|.;< afterwards comparing the quantities 



of oxymuriatic acid requisite to destroy the colour of 

 each. Dr. Rancroft proposes to compare merely the depth 

 of the cukjum, which the same proportion of each com- 

 municate to water a U-' ut be less accurate. 



Uimala indigo, and 



found that it contained other ingredient* besides the 

 true colouring matter. He obtained from it, by hot wa- 

 ter, an onoxygenaled base ff indigo, with a green mat- 

 ter united to gum, some ammonia, and a little yellow 

 extractive, amounting in all to 12 parts in 100. From 

 the remaining M he obtained, by digesting with alco- 



hol, 30 parts, consisting of a green matter, a reddish Indigo, 

 resin, and a little indigo. By digesting the residue 

 with muriatic acid, he obtained 2 parts of red resin, "*"V 

 2 of carbonate of iron, 2 of red oxide of iron combined 

 with aluminous earth, and there remained 3 parts of 

 silex, and 45 of pure indigo. This last alone gave out 

 the beautiful purple smoke on burning, which charac- 

 terises indigo, and which is the substance itself in a 

 state of sublimation. When thus purified, it is of a 

 purple colour, a circumstance which is also observed to 

 take place with Prussian blue, when most condensed. 

 Bergman obtained 47 parts of pure indigo from the ar- 

 ticle of commerce, which, when distilled, yielded 2 

 pot* of carbonic acid, 8 of an alkaline liquor, 9 of 

 empyreumatic oil, 2'J of a charcoal, containing 2 parts 

 of oxide of iron, and 2 of i!ex. 



Some have attributed the blue colour of the indigo 

 to iron, but this is improbable. Chaptal ascribes it to 

 charcoal ; but the mode of combination in which the 

 colouring matter exists, is so peculiar, that we ought 

 not to ascribe it exclusively to one principle. One 

 thing in it remarkable, is, that the compound base shews 

 _'er affinity among its components parts, than that 

 which takes place between it and oxygen, as the base 

 may be obtained in a limpid state, in which it requires 

 only the addition of oxygen to impart to it the colouring 

 property. It is by beiu^ deprived of a part of its oxygen. 

 that it is rendered soluble. This was formerly done by 

 inning it with woad which had been fermented. A 

 ; decoction of weld, madder, and broom, was 

 first poured on the woad, and allowed to stand in a 

 proper temperature, till blue veins were formed on its 

 surface. Quicklime, and the indigo in powder, arc 

 then added, and the fermentation conducted ttcundum 

 ariem ; the liquor become* green and fit for dyeing. 

 This process] is employed in dyeing woollen stuffs ; but 

 the proportion of lime requires to be carefully adjusted. 

 When in excess, it impart* to it a brown colour. For 

 the same purpose of disengaging the oxygen, or a part 

 of it, urine is employed, also metallic salts, such as 

 green sulphate of iron, in which the metal is at an in. 

 ferior degree of oxydation : artenic and oxide of tin are 

 used for the same purpose, or metallic tin assisted by 

 the muriatic or other acids. The substance chiefly em- 

 ployed a* a solvent of indigo, without depriving it of its 

 oxygen, or imparting any temporary change of colour, 

 is Milphuric acid. These processes form part of the art 

 <>f I >s CINO, and to that article we refer for the detain). 

 See Dr. Bancroft's IltitartkuOHKtrning ihe Ptiiloiopfiy 

 of Permanent Colaun. CHEMISTRY, vol. vi. p. 1 18; ana 



15. (//. D.) 



INDBB, the name of one of the central departments 

 ice, which derive* its name from the river Indrc, 

 with which it is traversed. It is bounded on the north 

 by the department of the Loire and Cher, on the east 

 by that of the Cher, on the south by the departments of 

 ('reuse and I'nper Vienne, and on the west by those of 

 Vienne, and the Jndrc and Loire. This department is 

 about 54 miles from north to south, and 45 from east 

 to west. It contains $6-2 square leagues. The western 

 part of the department abounds in rocks, pools, and 

 woods ; but the part on the right hand of the Indre 

 contains fine fields and vineyards, which afford grain 

 and excellent pasturage. There are iron mines, marble 

 quarries, and mineral waters in the department. The 

 contribution amounted to 1, 652,606 francs, and the po- 

 pulation to 207,1)11 inhabitants. Chateauroux U the 



,nl town. See i vol. ix. p. 6'75. 



IM)I!I. AMD LOIRE, is the name of one of the 

 western department* of France, which derives its name 



