COAIi-TAR COLORS. 76 COAL-TAR COLORS. acid, and the resulting compound is melted with caustic soda, yielding a sodium salt of alizarin. Ihis is soluble in water with a fine red color, but does not fasten upon any kind of fibre. If, how^- ever, cotton is previously impregnated with salts of aluminum, iron, or chromium, the alizarin will form insoluble salts ('lakes') with these metals; and as the precipitation occurs within the pores of the fibre, subsequent washing cannot remove it. Colors of tnis class of dyes are not suitable for silk and wool, but are very intense and permanent when properly applied to cotton. The Diphexyl-Amine Demvatives. These in- clude many varieties of dyes, such as the in- dulins, indophenols, thiagins, etc. Their chem- istry is too involved to be disposed of in a few words. It may, however, be mentioned that their characteristic groups are similar to anthraqui- uone, excepting that the oxygen of the latter is replaced by sulphur, imido-gi-oups, etc. The more important dyes of this class include 'methy- lene blue' and 'aniline black.' Indigo Dyes. By far the most important of these is indigo itself, a vegetable dye obtained from a tropical plant cultivated in India since the earliest times. The sap of this plant, when fermented under conditions excluding oxygen, yields indigo uhite, a soluble material having the formula CieHi.N.O,; if the fermentation proceeds in the open air, indigo blue, C,oHi„X,0;, is pro- duced. This substance is a derivative of the base called indol, CsH,?J", which occurs ready- formed, in small quantities, in many animal and vegetable .secretions. It can be prepared arti- ficially from aniline and chloraldehyde. When indigo' was found to consist of two indol mole- cules joined together and oxidized, the clue for the production of artificial indigo was at hand. It has since been found that any benzene deriva- tive having a nitrogenous group and a two- carbon group in the 'ortho' position may give rise to the formation of indigo. The first prac- tical method, devised by Baeyer in 1880, involved the action of potassium hydroxide on ortho- nitropropiolic acid: hut many other methods have been devised since then, such as the action of melted potassium hydroxide on bromace- tanilid, the action of halogenated acetone on aniline, etc. Indigo is one of the most reliable dyestufi's, both as to brilliancy and permanency, and there is little dilTerence in these respects between the natural and artificial products. The finished compound can, however, only be applied after reduction to the soluble indigo-white, and this makes its use in dyeing and printing some- what cumbersome. In some of the methods for preparing artificial indigo, the fibre can be im- pregnated with one ingredient and the other ap- plied either in the dye-vat or from the printing- rolls; consequently, indigo can be and is often directly prepared in the quantities and in the places in which it is needed. See Indigo. List of Colors. The following are some of the best known commercial coal-tar colors, their molecular formulas, and the principal methods employed in their manufacture. Aldehyde Green. — See Aniline Green below. Aniline Blaek, Ci„H,..N,, made by the oxidation of aniline with mineral salts. Aniline Blue (triphenyl - rosaniline hydro- chloride), C„Hn-,N,Cl. made by heating rosani- line, benzoic aeid, and aniline, and subsequently adding hydrochloric acid. Aniline Brown, Bismarck Brown, or Phenylene Brown (triamido-azobenzene), CuHisN,, made by the action of nitrous acid on metaphenylene- diamine. Aniline Green, or Aldehyde Green, CVHnNsSjO, made by the action of ordinary aldehyde on an aeid solution of rosaniline sulphate and the sub- sequent addition of sodium hyposulphite. Aniline Orange. — This name is a])plied to va- rious compounds made by the action of amido- sulphonic acids on phenols. The name is often applied to the so-called Victoria Orange, C,H„NA. .iniline Red. — See Fuehsin below-. Aniline Scarlet, CsHuNASNa, made by the action of diazoxylene on naphthosulphonic acid. Aniline Violet. — See JIauve'in below. Aniline Yellow (hydrochloride), Ci-HuNjCl, made by the action of nitrous acid on an excess of aniline. Alizarin, C.jH^Oj, made artificially by succes- sive treatments of anthracene with chromic acid and fuming sulphuric acid, and melting the product with potassium hydroxide. Among the dyes allied to alizarin are: Ali::arin Black, C,„HA-NaHSOs; Alizarin Blue, C,,B.,^0,; Aliz- arin Orange, Cj.HjNOa; and Alizarin Violet, or Galle'in, C:„H,„0,. Auramin (hydrochloride), CuHnNjOCl, made by the successive action of phosgene gas (carbon oxychloride) and ammonia upon dimethyl-ani- line. Atirantia (ammonium salt of hexanitro-di- phenylamine), Ci35N,0i,.NH„ made by the action of nitric acid on methyl-diphenylamine. Atirin, Ci,H„03, made by the action of oxalic and sulphuric acids on phenol. Benzaldehyde Green. — See Malachite Green be- low. Benzidine Red. — See Congo Red below. Benzopurpurins, dyes of various scarlet shades. They are chemically allied to Congo Red (which see below), and are made by treating salts of toluidine (which is m.ade from nitrotoluene, and is analogous to benzidine) with nitrous acid, and combining the resulting salts w'ith a- and /3-naphthylamine sulphonic acids. Bismarck Brown. — See Aniline Brown above. Blacklc;/ Blue. — See Indulin below. Bordeaux. — See Ponceaux below. Chryso'idin (hydrochloride), C,,H,3N,C1, made by the action of diazo-benzene chloride on meta- phenylene diamine in aqueous solution. Congo Rid, or Benzidine Red, C;,JI.,»N„S,0„Na,, made by the action of nitrous acid and then of sodium naphthionate on benzidine hydrochloride. Eosin, CaPeOsBr^K.. or C5„H„0,.Br,Na:, made by the action of bromine on fluorescein. Erythrosin, C^HsOsIiNai, made by the action of iodine on fluorescein. Fluorescein, C.„H,.Or., made by the action of phthalic acid anhydride on resorcin. Fuehsin. Rosaniline Hydrochloride, Magenta, or Aniline Red, C^H^oN^Cl. nitide by the oxidation of toluidine and aniline in the presence of acids. Galle'in. — See Alizarin above. EeJianthin. — See !Metliyl Orange below. Indigo. — See text of the article above. Indnlin. or Blackley Blue. C„H„,N„ made by heating aniline salts jvith amidoazobenzene. Magenta. — See Fuehsin above.
