PERKIN'S VIOLET , OR MAUVE.

189

quantity of water, and allow the readtion to proceed for twenty-four hours.The mixture becomes turbid, blackens, and at the end of the period hasresolved itself into a clear liquid, and a black precipitate containing mauveine(indisine), chromic oxide, and certain resinous impurities. The large woodenvessels in which this process takes place are then filled up with boiling water.The whole is well stirred up and allowed to settle. The water, which containsthe excess of bichromate of potash and certain soluble impurities, is thencarefully decanted off. The washing is thus repeated four times, and theblack precipitate containing the colouring matter is then colledted upon filters.It is washed twice or thrice with water slightly acidulated with sulphuric acidand then with cold water. The precipitate is then boiled with water in largevats for three hours and often stirred. The liquid, which holds the colouringmatter in solution, is drawn off by decantation and filtration. This treatmentis repeated until nothing more can be dissolved. These aqueous solutions,mixed and filtered, are precipitated by an alkali or an alkaline salt. Theprecipitate, colledted on a filter, is washed with luke-warm water to removeexcess of the precipitating salt and a certain reddish colouring matter. It isfinally converted into acetate of mauveine by the addition of the necessaryquantity of acetic acid. To obtain the acetate pure, this process of solution,precipitation, and washing must be several times repeated. By this pro-cedure 100 kilos, of baraniline yield 75 to go kilos, of mauve in the state ofthick paste.

The seledtion of aniline is a very essential matter for the preparation ofmauve. The anilines suitable for it are not the same as those which give thebest results for magenta. The mauve prepared according to the process justdescribed, though fit for pradtical purposes, is not chemically pure. If requiredin this state it must be boiled in a large quantity of water, and then filtered.From the solution the colouring matter is thrown down by means of an alkali.The precipitate thus obtained should be colledted upon a filter, washed withwater until free from alkali, and dried. When dry it is to be dissolved inabsolute alcohol, the solution filtered, and then evaporated to dryness on awater-bath. The mauve thus obtained is a brittle substance, with a beautifulbronzed surface ; but if some of its alcoholic solution be evaporated 'on aglass plate, and viewed by transmitted light, it is of a fine bluish-violet.Mauve forms a remarkable compound with tannin. If an aqueous solutionis mixed with a solution of tannin, precipitation takes place; the pre-cipitate, after having been well washed, no longer possesses the properties ofthe pure colouring matter, but is insoluble in water, and dissolves in concen-trated sulphuric acid, forming a dirty green liquid; but on adding an excess ofwater to this solution the new compound is precipitated unchanged. Withthese tannates dissolved in acetic acid, Messrs. Clift, Lowe, and Calvert dyedspecimens of silk, wool, and cotton, which the latter gentleman exhibitedearly in the year 1858 before the Society of Arts.

Among the very large number of new methods proposed for the manufadtureof this dye, especially after the spring of the year 1859, we may notice thefollowing:—Messrs.DepouillyandLauth’smethod (patentedin June, i860)con-sisted in adding to a salt of aniline a solution of chloride of lime, which yieldeda purple insoluble precipitate. This was repeatedly washed in slightly acidulatedwater, dissolved in concentrated sulphuric acid, and re-precipitated by the