INhlfiO. 



INDIGO. 



The solubility of white indigo in a dilute alkaline nolution, and the 

 intolubility of blue indigo in a similar menstruum, are facts of great 

 interwt and importance, a* on them depend the IIM of indigo in the 

 aru of dyeing and eaUoo-printing. The deoxidising agents, other than 

 grape sugar, that are used for making the rrduml indiyn rait, are 

 protosulphate of iron, protochloride of tin, orpimrnt, and decaying 

 vegetable matter ; lime tometimes replacing the alkali. For details of 

 the preparation of some of these bath* or vata, aee CUUDO-BUROra 

 and DTICCO. 



Slpli*JijVtie atid, or >W/<Ain</^iV oo</ (In,S,0. = C,. J.0,,8,0,). 



One equivalent of hydrogen in this compound is replaceable by an 

 equivalent of metal.' forming salts called niphindigotata or tulph- 

 imliila'ft. Sulphindigotic acid i* formed by dissolving commercial 

 indigo in six time* iu weight of fuming or Nordhatiscn sulphuric acid. 

 The product is known as Sajnmy blue, and is extensively used in cloth 

 dyeing ; it contains another acid named hypotntpkiditiotic u 

 the greaU-r part of the residue from its preparation consists of W/>/H>- 

 jmrptric or nJpkopkaiiric add <2C l( H t NO tl 8 t O ( ). Br th* dsoompo- 

 aition of these sulphuric derivatives of indigo there ore produced 

 nJfJkmriJir, ndpkataric, inlphufttlric, and tulphorufc acidt : they have 

 been but little studied. 



I MI IK (C,,H,NO,>, a substance obtained from indigo by the addition 

 of two equivalents of oxygen. 



C..II.NO. 



Indigo-blur. 



= C..H.KO. 



lutin. 



In order to prepare it, powdered indigo is to be mixed in water with 

 equal parts of sulphuric acid and bichromate of potash, the last being 

 dissolved in 20 or SO part* of water. The indigo dissolves, and at first 

 without the extrication of any gaseous matter, but towards the end 

 with the disengagement of carbonic acid gas, and the formation of a 

 deep yellowish brown liquid, from which the isatin separates by evapo- 

 ration, in 'crystals ; these are purified by repeated crystallisations in 

 water, and one and the last in alcohol. Nitric acid may be used in the 

 place of chromic for oxidising the indigo, but if too concentrated, 

 indigotic acid (nitrosalicylic acid) results. 



The properties of isatin are : It crystallises in prisms, which are of 

 a yellowish red or deep aurora-red colour, possessing much splendour 

 when deposited from an alcoholic solution ; they are slightly soluble in 

 cold water, but dissolve readily in boiling water and in alcohol ; these 

 solutions discolour the skin, and impart a disagreeable odour to it. 

 The crystals are decomposed by heat, leaving a charcoal which it is 

 difficult to incinerate ; the caustic alkalis convert it into isatic acid. 

 Fused with solid hydrate of potash it is decomposed, aniline being 

 produced according to the following equation : 



C,.H t !JO. + 4(KOHO) a C,,H,N + 4(KO,CO,) -f H, 



1- -' .::. 



Aniline. 



Chlorint and Bromine dcrimtvrtt of Iiatln. One or two atoms of 

 hydrogen in isatin may be replaced by one or two atoms of chlorine or 

 bromine, and the following compounds formed : 



ChloriMtln 

 Diehloriutln 

 BromlHtln 

 DlbromlMtin 



These compounds greatly resemble isatin, both in appearance and in 

 all their reactions. The chlorine derivatives are produced by the 

 action of chlorine upon indigo, and separated by crystallisation from 

 alcohol, chlorisatin being less soluble in that liquid than dichlorisatin. 

 The -bromine derivatives are obtained in a similar manner from indigo, 

 using bromine instead of chlorin*'. 



/Ki<r<Kiy(C,.H : N't m.C,.H.NO.). Isatin dissolves in potash 

 with a deep purple colour, which becomes bright yellow by heat The 

 solution yields by evaporation a crystalline salt of potash, which in 

 < in alcohol, and crystallises in small, hard, colourless prisms. 

 When a solution of this salt in mised with one of acetate of lead, a 

 white precipitate is obtained, which, diffused in water and decomposed 

 by hydrosulphuric acid, yields a colourless acid liquid, and ilii- by 

 spontaneous evaporation furnishes a white and scarcely crystalline 

 powder, which u liydrated isatic acid. 



The properties of iwttic acid are as follow : It is perfectly insoluble 

 in cold water ; but when heated in water, it is decomposed into isatin 

 and water, the mixture becoming of ,1 n-ddish yellow rolour . the 

 noluMv isatatos act in the mm<- manner with tin- mineral acids ; win n 

 thrT are added t it wild, no decomposition i* apparent; but as soon 

 U applied, tho mixture becomes yellow, and deposits crystals 

 of isatin. 



IstUte of poUah gives a white precipitate with barytie salts, soluble 

 In boiling water; with the salt* of silver It gives a white precipitate, 



which dissolves when heated in the mixture, a certain portion of the 

 silver salt being reduced to the metallic state ; tho boiling solui ; 

 isatato of silver deposits crystals which are partly in lamina- and partly 

 granular. The general formula of these itatata is (C. 

 MO,C,.H.NO,). 



CUoric and Jiromine derivaiira of Italic Add. These are 



CblorUmtic scld 

 Dichluriutie uid 

 Bromifatic scid 

 DibromUaUn scld 



. C,,H,C1XO, 

 . C,.H,CI,SO. 

 . C 14 H,BrXO. 

 . C l( H l Br t NO ( 



They are respectively produced by the action of potash upon chlori- 

 satin, dichlorisatin, bromisatin, and dibromisatin, the potash salt of 

 the acids being thus formed, and this, by double decomposition with 

 the soluble salU of other bases, furnishes the several metallic derivatives 

 of these acids. 



A mmrmiacal Derirativet of f satin. Ammonia acts upon isatin, giving 

 rise to bodies that d i Her from each, according as the circumstances differ 

 under which they are brought into contact. They all contain the ele- 

 ments of isatin, plus ammonia (XH,) and minus water (HO). Their 

 piiii.'iis to each other are best shown by formulating them upon the 

 ammonia type, or upon the hydnited oxide of ammonium t\ 

 follows, in which blue indigo that is, the radical iV 

 is represented by the signs (Inln or In,). 



In 

 Imetatin . . . C lt H t y 1 O, X { In 



Itnaiatin 

 Isamlc acid 

 Isamide . 

 Isatimido . 



,. - 



?>.<>, 



HO/ 



NIB II i> 



NIn.H.O ) 

 *' 



InO ) 



r n N o - NIn . i 

 C I H >' N - NIn,H,0 i 



Each of the chlorine and bromine derivatives of isatin gives rise to a 

 similar class of bodies, in each of which, of course, isatin is replaced by 

 the chlor or brom derivative. 



Imesalin is obtained in colourless prisms on passing a current of dry 

 ammoniacal gas through a solution of isatin in absolute alcohol. 

 Imruatin is produced when a solution of isatin in ammonia is main- 

 tained for a short time at the boiling point. It crystallises in lamellar 

 grains, /ramie, called also inuualic and rubetutinic add, crystallises 

 out in beautiful platen from an alcoholic solution of isamate of ammo- 

 nia, to which hydrochloric acid has been added. Isamate of ammonia 

 results from the metamorphosis of instate of ammonia when a solution 

 of the latter salt is evaporated to the consistence of a syrup. Bromine 

 energetically attacks isamic acid, producing a yellow body termed 

 itidflikromt. Itnmidc, or atnatatin, is formed when isamate of ammo- 

 nia is strongly drie<l. Imlimidt is a crystalline yellow powder formed 

 during the preparation of imesatin, but is more soluble in the alcoholic 

 ammonia, and therefore crystallises out subsequently to the imesatin. 

 There appear, also, to be produced at the same time, ualilime 

 (C,,H IO N < 10 ), containing three atoms of isatin, plus one of ammonia, 

 minus two of water ; and amuatin (C^H^NuO,,), represented by six 

 atoms of isatin, plus five of ammonia, minus six of water. 



Itathyd (C ln H NO. = C t ,H.NO., H). This body may be viewed an 

 the hydride of isatin, bearing the same relation to that body that white 

 indigo does to blue. It is best prepared by placing isatin in a flask 

 with ziiic and dilute sulphuric acid. H in a grayish crystalline powder, 

 insoluble in water and sparingly so in alcohol or ether. On passing a 

 current of sulphuretted hydrogen through the alcoholic solution, bitut- 

 /ihi/tcithyd (C 18 H NO,S t ) U formed, a body in which two atoms of 

 sulphur replace two of the oxygen in isathyd. On adding nolm 

 potash drop by drop to an alcoholic solution of bisulpl, 

 atom of sulphur is substituted by one of oxygen, and m//i///' 

 produced. By the action of hydridiaing agents upon the chlorine 

 :.ud bromine derivatives, corresponding chlor and brom itathyd* are 

 obtained. 



luttane (C v H,,N,O a ) is a white powder, formed when bi.tulphisathyd 

 is boiled with bisulphite of ammonia. It contains the element- 

 molecules of isathyd, less two atoms of oxygen. 



ludin is prepared by the action of potash on Kiilpliixathyd, the alkali 

 being subsequently removed by hydrochloric acid. It is pulverulent, 

 of a very fine deep rose-red colour, insoluble in water, anil slightly 

 soluble in alcohol and ether. When heated, it begins to (well as soon 

 as it melt*. It yields a substance which crystallises in needles, and 

 much charcoal remains. Boiling nitric acid decomposes it, altering its 

 odour slightly , red vapours are I'mim-d. iin^ ' >N,0 4 ) 



ti produced. If the ebullition be continued, the new product is also 

 dsoomposed, snd disappears, Sulphuric TI. .i^nnniiL,' 



I mi-, nnd walvr precipit.il. - it from solution unaltered; bromine 

 colours it violet. Ammonia hax no action on indin. but polish attacks 

 it under certain cirruin- I' lo with blue indigo, and 



''II '. 



