ANILINE REDS.

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decolourises the salts of rosaniline. Permanganate of potash transforms thesolutions of rosaniline and its salts into liquids which give merely a yellowdye. Rosaniline, whether free or in combination with acids, if dissolved andsubmitted to prolonged ebullition along with oxidising agents,—such as per-oxide of lead, bichromate of potash, alkaline and alkaline earthy nitrites, andperoxide of barium,—is transformed into other colouring matters, brown ororange-red, according to circumstances.

The hydrochlorate of rosaniline, known as fuchsine, as obtained by theabove process, although sufficiently pure for many operations in dyeing andprinting, requires for certain purposes further purification.

The simplest manner of preparing free rosaniline is to dissolve the hydro-chlorate in boiling water, and to decompose it by means of a slight excess ofan alkaline solution, also boiling. Ebullition is kept up for some hours ; theliquid is filtered, and on cooling deposits magnificent crystals of rosaniline,almost colourless.

The acetate of rosaniline, known commercially as roseine, is the most im-portant salt of this base. The rosaniline employed in its preparation shouldbe pure and crystalline. It must be completely freed from the excess of alkaliused in its preparation, dried, and pulverised. The acid should be entirelycrystallisable, perfectly pure, and free especially from sulphuric and sulphurousacids. Calcareous waters should also be avoided. The rosaniline, fresh fromthe drying-stove, is placed in vessels of enamelled cast-iron, heated in thewater-bath or by steam. Acetic acid is very gradually added, the mixturebeing carefully stirred till it becomes quite homogeneous. To promote com-bination the whole is heated to 60° or 70° C. Boiling water is then rapidlypoured upon the semi-fluid mass, and it is kept in ebullition for some minutes.The liquid is run into crystallising vessels, set in a cool place not subjedt tovariations of temperature, and after standing a few days deposits fine crystalsof roseine. The best proportions are 20 parts of crystalline acetic acid toioo parts of rosaniline. To dissolve these 120 parts of acetate of rosaniline,240 to 250 parts of water are needed. The heat must be carefully managed,to avoid loss of acetic acid by volatilisation. Too prolonged boiling wastesthe acid, and determines the formation of sub-salts which cannot be made tocrystallise.

Roseine can also be formed by double decomposition, adding the solutionof the crude arseniate, sulphate, &c., of rosaniline to a solution of acetate oflead. The method is unprofitable, as the precipitated lead forms a lake witha part of the colouring matter, which is thus pradtically lost.

Violaniline, mauvaniline, and chrysotoluidine are invariably present in smallquantity in crude rosaniline as prepared by the arsenical method. Thesebases form colledtively about one-half of the colouring matter contained inthe crude produdt. When separated they furnish useful dyes. For theprocess of their isolation we must refer the reader to the work of Girard andDe Laire, “ Traite des Derives de la Houille,” p. 575.

We must now turn to the pradtical application of magenta in dyeing andprinting. It is abundantly used, not merely in rose, pink, and red shades, butin a variety of compound colours. Like most of the coal-tar colours, it hasa strong affinity for animal tissues, upon which it produces solid shades with-out the aid of a mordant. Vegetable fibre, on the other hand, acquires merely