232 ANILINE AND ANILINE DYES.— Manufacture of Aniline Blues.

two hours, the temperature being then raised to 250°C. When the required shade is attained the semi-fluid mass is poured into a mixture of 4 parts alcoholand 12 hydrochloric acid; the brownish cooled massis then powdered and boiled for fifteen minutes withdilute sulphuric acid, and filtered. The residue isboiled twice successively with hydrochloric acid toeliminate the last traces of red tinge.

Bardy describes the following manufacturing pro-cess:—Kosaniline hydrochloride, 100 parts, sodiumacetate, 30 parts, crystallized potassium acetate, 10parts. The first two ingredients are mixed and eva-porated to dryness; the potassium acetate and somefree aniline are then added, and the whole heatedto 175° C. till a pure blue tint is developed. Theproduct is then treated with one and a half times

Fig. e.

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its weight of strong hydrochloric acid; this leavesthe blue undissolved. The insoluble substance iscollected, washed with water, and treated with fivetimes its weight of caustic soda ley at 32° C. Aftertwenty minutes boiling 15 parts of boiling water areadded and the whole filtered. The free base thusproduced is washed with lukewarm alcohol to removemono- and di-phenyl rosaniline, and then treatedwith sulphuric acid.

The hydrochloric acid solution yields a precipitateof diphenyl rosaniline in dilution with water equalto 1^ parts per 1 part of crude blue; on furtheradding 23 parts of water, monoplienyl rosaniline isthrown down. The mother liquors are saturatedwith lime and mixed with acetate and chloride ofsodium to recover rosaniline hydrochloride.

The process as carried out at the present dayis thus described by Girard and De Laihe: —Anenamelled retort holding about 20 litres is heated ina paraffin bath, a coliobator and distilling worm areattached to the top (which is movable), and anagitator is provided.

Fig. 6 shows the apparatus in section throughthe axis; a, enamelled cast-iron retort; b, paraffinbath ; c, d, e, agitator; the top part ( d ) helical, thelowest portion (e) provided with curved arms fur-nished with projections almost touching the bottomof the retort to prevent adhesion of materials; /,'movable top: g, flange and screw nuts; h, packingbox of agitator axle; i, thermometer ; j, orifice withwhich the coliobator and condenser are connected,either being shut off at will by suitable taps; k, colio-bation worm (the distilling worm is below on theopposite side of the retort); /, tube for blowing steamthrough (a hollow agitator axle may also be used);m, n, pulley and cog-wheels.

Five kilos, of acetate of rosaniline and 15 of anilineare introduced into the retort, which is then heatedto 170° C. for about two hours. Samples are takenfrom time to time by introducing acid through atubulation provided for the purpose. A drop is placedon a white porcelain dish, and a drop of alcohol andacetic acid added. When the operation is completea pure blue colour should result; if a strongly markedred margin is perceptible, the action has not gone onlong enough; if the aureole is not of a bright rose,but is brown or grey, the operation has been carriedon too long. By practice the workman is able to hitthe exact point when the product is not quite liquid,but is perfectly homogeneous, the blue being whollydissolved in the excess of aniline. This excess (threeand one-fourth times the theoretical amount) is de-sirable, as it enables a constant temperature to bekept up by rendering the whole tolerably fluid, andthus greatly promotes the action and improves theproducts. A number of these retorts may be con-veniently connected with one condensing worm andworked together.

Direct Blue. —To prepare this dye all that isrequisite is to free the mass from aniline. This isreadily accomplished by blowing steam through, orthe colour may be dissolved out by acids.

Purified Blue. —The crude product is diluted withalcohol (methylated spirit or wood spirit), and run ina thin stream into water acidulated with hydrochloric,acetic, or sulphuric acid. The blue is precipitated asa fine powder, most of the brownish impurities andbye products being retained in solution by the slightlyalcoholic solution of aniline salts thus produced. Theblue precipitate is then washed with boiling slightlyacidulated water, and is fit for the market.

Night Blues (Bleus lumieres) are prepared bywashing the purified blues with warm alcohol, anddissolving in boiling alcohol. To the filtered liquidis added alcoholic ammonia or soda, when triphenylrosaniline is precipitated in a state of considerablepurity. The precipitate is then washed with boilingwater and dissolved in the particular acid the salt ofwhich is required. Bleus lumieres are also sometimes