INDICTION INDIGO. 



79 



writers; but Barrow, who visited the southern ex- 

 tremity of Africa at a subsequent period, fully con- 

 firms its truth. He says, that every one there is too 

 well acquainted with this bird to entertain any 

 doubts of the fidelity of Sparmann's narrative. It 

 is also confirmed by Le Vaillant, who states that, on 

 account of the important services which it renders to 

 the Hottentots, they were very unwilling that he 

 should destroy one of them. 



INDICTION, in chronology; a period of fifteen 

 years, reckoned in succession, and used by the 

 llomans for appointing the time for the payment of 

 certain taxes. Three sorts of indiction are men- 

 tioned; 1. the Caesarean, which fell on the 8th of the 

 calends of October, or the 24th of September; 2. the 

 indiction of Constantinople, which was instituted by 

 Constantine, A. D. 312, and began on the 1st of 

 September; and 3. the pontifical or Roman, which 

 begins on the calends of January. It has no con- 

 nexion with the motions of the heavenly bodies. 

 We find ancient charters in England also dated by 

 indictions. 



INDICTMENT. An indictment, according to 

 the English law, is a written accusation of one or 

 more persons for a crime or misdemeanour, preferred 

 to, and presented upon oath by a grand jury, to a 

 court. In determining whether there is a reasonable 

 cause to put the accused upon his trial, the grand 

 jury hear evidence in support only of the charge; 

 and if twelve of them are satisfied of the truth of the 

 charge, the indictment is then said to be found, and 

 is publicly delivered into court. If the grand jury 

 think the accusation groundless, the accused is dis- 

 charged; but a new bill of indictment may be pre- 

 ferred to a subsequent grand jury. 

 INDIES, WEST. See West Indies. 

 INDIGESTION. See Dyspepsia. 

 INDIGO. The knowledge of this most valuable 

 vegetable substance, which forms an important part 

 of East and West Indian commerce, and is beginning 

 to receive considerable attention as an American pro- 

 duction, is alike interesting to the chemist and to 

 the dyer. The ancients were acquainted with it 

 under the name of indicum. Pliny knew that it was 

 a preparation of a vegetable substance, though he 

 was ignorant of the plant which furnished it, and of 

 the process by which it was prepared. From its 

 colour, and the country from which it was imported, 

 some authors call it atramentum indicum, and indicum 

 nigrum. The American name is nil, or anil, from 

 which the Portuguese have adopted their anileira, 

 the other European nations generally call it indigo. 

 The Arabian name is nile, and the Chinese, tien 

 laam, or sky blue. 



In treating of indigo, it will be the most convenient 

 to explain, in the first place, its physical and chemical 

 properties, and afterwards to allude to the sources 

 from whence it is derived, and the method by which 

 it is manufactured. As it is found in commerce, it 

 presents the form of little square or oblong cakes, of 

 an intense blue colour, approaching to black; is 

 brittle and friable; rather light, and without taste or 

 odour. It is volatile, with a disagreeable odour, 

 subliming at 550 P., a degree of heat near that at 

 which it is decomposed. Its vapour is of a rich 

 violet-red colour, and condenses by cold into delicate 

 acicular crystals, which consist of perfectly pure 

 indigo. Water, by being boiled on indigo, dissolves 

 only about a ninth or twelfth its weight; the solution 

 is of a reddish-brown colour, and contains what may 

 be called the extractive part of the substance; but 

 the colouring matter remains unaltered, except in 

 having assumed a brighter hue. Alcohol and ether, 

 when digested upon it, also are attended with similar 

 effects. S'llphuric acid is the only single agent that 



dissolves indigo without destroying its colour. When 

 it is put into this acid, a yellow solution is at first 

 formed, which, after a few hours, acquires a deep 

 blue colour. From the solution, diluted with water, 

 potash and its sulphate throw down a deep dark-blue 

 precipitate, capable of imparting to water, containing 

 only sooW of its weight, a distinctly blue tinge. 

 It is no longer subject to vaporization, however; from 

 which circumstance, and its property of solubility in 

 water, it is inferred to be a different substance from 

 indigo, and has received the name of cerulin. Its 

 composition is believed to be one equivalent of indigo 

 and four of water. When properly diluted with water, 

 it forms the liquid blue, or Saxon blue, of the dyers. 

 Another compound of indigo and water, under the 

 name of phenecin (from 0<w, purple), is obtained 

 when water is added to a solution of indigo _ in sul- 

 phuric acid, which has been suffered to stand for 

 several hours, till it has lost its yellow colour, and 

 become blue. It appears to consist of one equiva- 

 lent of indigo, and two of water. In the formation 

 of these substances, indigo is conceived to combine 

 with water; but whether the water is afforded by 

 the sulphuric acid, or whether the sulphuric acid 

 operates merely to prepare the indigo for combining 

 with water afterwards, is not yet fully determined. 

 When indigo, suspended in water, is brought into 

 contact with certain deoxidizing agents, it is deprived 

 of a part of its oxygen, becomes green, and is ren- 

 dered soluble in water, and still more so in the alka- 

 lies. It recovers its former colour, however, on 

 exposure to the air, by again absorbing oxygen of 

 7 or B of the whole weight of the resulting indigo. 

 Its deoxidizement is effected either by allowing it to 

 ferment along with bran, or other vegetable matter, 

 or by decomposing in contact with it the protosul- 

 phate of iron, by the addition of lime. Substances 

 dyed by deoxidized indigo receive a green tint at 

 first, which becomes blue by exposure to the air. 

 This is the usual method of colouring cloths by 

 means of indigo, which, when fully oxidized, affords 

 a permanent dye, not removable by soap or by acids. 

 Chlorine, whose power in extinguishing vegetable 

 colours is universal, destroys the colour of indigo ; 

 and, from the known fact that the same quantity of 

 free chlorine discolours always the same quantity of 

 pure indigo, a solution of Indigo in sulphuric acid 

 has been employed for measuring the strength ox 

 solutions of chlorine and of chloride of lime, in order 

 to regulate their application to the art of bleaching; 

 and, reciprocally, a solution containing a known 

 quantity of chloride of lime may be employed as a 

 test of the strength or value of indigo. Indigo, puri- 

 fied by sublimation, is composed of 73.26 carbon, 

 13.81 nitrogen, 10.43 oxygen, and 2.50 hydrogen. 



Indigo may be said to be a rare production of the 

 vegetable kingdom, it hitherto having been found only 

 in a small number of species belonging to the genera 

 indigo/era, isatis, and nerium; but it is almost ex- 

 clusively from the first of these that the indigo of 

 commerce is extracted. The species of indigo/era 

 are leguminous plants, herbaceous or shrubby, with 

 alternate and generally pinnate leaves, and small 

 blue, purple, or white flowers, ordinarily disposed in 

 axillary racemes. They are very numerous in the 

 equatorial regions of the globe. The species most 

 commonly cultivated are the /. anil, a native of tro- 

 l America, according to the latest authority, but 

 low cultivated even in the East Indies; the /. tinc- 

 toria, also cultivated in both Indies; and the /. ar- 

 gentea, which is the species employed in Barbary 

 and Egypt. The /. tinctoria is the species most 

 abundantly cultivated. 



In describing the culture of the indigo plant, and 

 the mode of manufacturing the indigo, we shall draw 



