Besides diphenylamine, ditoluylamine, phenyl-toluylamine and diphenyl-asnyl-amine may be used. These may also be treated with oxalic acid for the same purpose. The development of colour is watched by drawing samples ; it is complete when a copper red is pteduced, and the cooled mass becomes hard and brittle, and dissolves in alcohol with au intense blue. It is purified by dissolving at 100° (212° F.) fa double its weight of aniline ; the solution is thrown into a large quantity of benzol, kept' well agitated ; the vessel is kept 000l, so as to avoid loss of benzol. The blue is precipitated as a very fine powder, collected on a canvas strainer to drain, and well pressed ; it is repurified in the same way without being pressed, and is washed on the strainer with benzol. It may be further purified by dissolving in boiling aniline ; procipitated by hydrochloric acid, the aniline salt is washed out with boiling water. The free base is obtained by caustic soda, and purified by solution in alcohol.
The separation of blue from violet colouring. matter is effected by dissolving in ten times its weight of oil of vitriol heated to 30°-60° (86°-140° F.). Water is added to precipitate the blue, whilst the violet remains in solution ; it is thrown ou to an asbestos filter, and washed with dilute acid, then water; it is drained and pressed, and if required with greater purity, the previous process is carried out.
Toluidine Blue, or Tri-toluyl-rosaniline.—The composition of this blue is analogous to that of tri phenyl-rosaniline, and its mode of preparation is shnilar. Equal parts of rosaniline and crystal lized toluidine are heated for five or six hours to 150°-174° (302°--346° F.). Its extraction and purification may be effected with hydrochloric acid and water. It dissolves le alcohol with a beau tiful blue colour.
Bleu de Coupier,or Triphenyl-roso-toluidine.—Toluidine red heated with aniline yields a blue colour ing matter, known by this name. It is prepared in the same way as Coupier's reds (q. v.), by substituting his toluidine rid for rosaniline.
Bleu de Paris.This is obtained from methyl-auilines and anhydrous bichloride of tin ; it is a triplienyl-rosaniline. (See Violet de Paris.) Aldehyde Blue.—This colouring matter is a valuable Boum of green, and although its merit as a blue does not entitle it to the notice of the dyer, its preparation must be noticed here. A solution of 20 grms. rosaniline, in 280 cc. ordinary hydrochloric acid, is diluted with an equal volume of water, and mixed with 100 cc. crude aldehyde. After twenty-four hours, the blue is precipitated by caustic soda in excess, colleoted on a filter, washed, purified by solution ia alcohol, and dried. A yellow resinous matter is removed by carbon bisulphide. Its solution iu wood-spirit dyes well, but not deeply. (See Aldehyde Green.) Bleu de MuMouse.—This product, having the colour of ammoniuret of copper, is obtained by boiling 50 grms. bleached shellac, and 18 grms. soda crystals, in 1 lit. water, and adding 50 cc. solution of magenta (1 part magenta in 4 parts water, and 4 parts alcohol), boiling for one hour, and adding water and spirit as they boil away.
Asurine.—Bluzner Zwelfel makes this colouring matter as follows :-100 grms. starch is boiled in
1 lit. water, and whilst boiling, 4 grins. ohlorate potash, 3-4 grms. sulphate iron, and 10 grms. sal ammoniac, are added. When the mass has cooled and set, 60 grms. of a salt of aniline is added, and well mixed and dissolved. Its tints are altered by varying the proportions.
Triphercyl-Mauvandine.—This base is converted into ethyl, methyl, and phenyl oompounds in the same way as rosaniline ; it is soluble in alcohol, and its salts yield splendid blue colouring matters. (See Triphenyl-rosaniline, Rosaniline residues, and Mauvaniline.) hfauveine, Mauve, Aniline-blue, or Perkin's Violet. C„E1,4N4.—The production of this interesting colouring matter depends upon tho adieu of an oxidizing agent on aniline, or a salt of aniline, such as the sulphate or chloride_ A cold satumted solution of sulphate aniline is mixed with an equal quantity of a oold saturated solution of bichromate potash, and allowed to stand for 10-12 hours. The quantity of potash is such as to produce, with the sulphuric aoid from the aniline salt, the neutral sulphate. The mixture is thrown on to a filter, and washed until the potash-salt is all removed ; the residue is dried at 100° (212° F.). The adhering resinous matter is washed away with coal-tar naphtha or petroleum, and when the naphtha has evaporated, the washed mass is dissolved in wood_ naphtha or methylated spirit. Instead of washing away the resinous matter, it is more economical to treat the crude mass with slightly dilute wood-naphtha or methylated-spirit ; as the resinous impurities are but slightly taken up, the larger proportion of the spirit 'is recovered by distillation, and an aqueous solution of the colouring matter remains ; by evaporation, it can be obtained either in a dry crystalline state, or in paste. Caustic potash, added to a solution of the sulphate, precipi tates tlie mauveine, which is almost insoluble in water, but dissolves readily in alcohol, yielding a bluish-purple colour. It is a powerful base, combining with acids to form well-defined salts, which have a fine rnetallic lustre ; it expels ammonia from its combinations.
When the base is heated with aniline, ammonia is given off, and a blue colouring matter is formed. It has been proposed by Perkin to obtain an ethyl compound, by heating equal parte of mauveine and iodide ethyl together, for the general carrying out of this (see Hofmann's violet, &c.); it was largely used a short time ago, but the replacement of iodine by less costly methods of intro ducing the alcohol radicals must eventually restrict its use. It dyes deeper and finer shades of mauve.
By oxidizing a hot solution of mauve with sulphuric acid and manganic oxide, a beautiful red colouring matter is produced ; it is very soluble in water, and forme crystals having a fine beetle green lustre. In concentrated sulphuric acid, it dissolves with a dark green colour, which, on adding water in small quantities, changes into bluish green, pure blue, violet, purple, and at last into pure red. This was originally called " safranine" ; but the colouring matter now met with in commerce under that name is obtained from a very different source.