238 A MI,INF, AND ANILINE DYES

—Manufacture of Aniline Violets.

precipitate. The precipitate is pressed, dried, anddissolved in strong hydrochloric acid; water is thenadded, when the violet is precipitated and washedwith pure water and dried, whilst the rosanilineremains in solution. The henzol containing anilineis treated with hydrochloric acid to throw downaniline hydrochloride and colouring matters, and isthen distilled over an alkali.

Instead of running the mass into benzol, it maybe slightly diluted with alcohol and run slowly intoacidulated brine; an impalpable powder then pre-cipitates, which is well washed with fresh acidulatedbrine, and finally with pure water, after which itis pressed and dried at a temperature not above40° C.

Blue Violet. —The operation is conducted just asfor violet, using, however, a little more aniline (twicethe weight of rosaniline salt, i.e., 20 kilos, anilineand 10 rosaniline salt), and allowing a somewhatlonger time, viz., from twenty to thirty minutes,so that the operation lasts one and a half to twohours. Too high a temperature must be carefullyguarded against during the last quarter of an hour,and the sample must be drawn at very short inter-vals. When finished the mass is slightly cooled, and4 to 5 litres of alcohol gently run in with continualstirring. The whole is then jioured into 400 litresof alcohol acidulated with hydrochloric acid; afterwhich brine is added to throw down the colour.Rosaniline and some violet red remain dissolved.The precipitate is washed first with dilute acid, andfinally with pure water, till no longer acid. If theheating operations have been pushed too far theproduct is slightly resinous, and should be washedwith weak alcohol; as also if the shade is a little toored. If much insoluble matter is present, the wholeshould be dissolved in strong alcohol in an agitatingapparatus.

Manufacture of Hofmann's Violets. — The threevarieties, marked It, B, and B B, of these violets,are prepared in much the same way, the chief dif-ference in the processes being the proportion ofthe alcoholic iodide used. In the early days of themanufacture the process was conducted under theordinary atmospheric pressure, in a digester pro-vided with a cohobater and condensing worm andan agitator, and surrounded by a steam jacket. Atthe present day autoclaves are usually employed,and the action is brought about under a greatlyincreased pressure. After about two hours’ heatingat about 115° to 130° C., the operation is finished.The alcohol and excess of iodide is distilled off, andthe residue is ready for the market if the hydrodidesof the resulting bases are required.

Instead of heating by steam a saline bath may beused. Thus, a solution of calcium chloride may beused, or even brine. If the temperature be lowerthan the above, a longer time is requisite; thus, fouror six hours, or even more, at 100° to 110° C., is re-quired. When the digester is opened permanentgases (ethylene and metliylic ether?) escape; themanhole must therefore be opened cautiously, other-wise effervescence and loss of material ensue. For

the three qualities the following proportions may beused (Girard and De Laire) :—

K B BB

Kosaniline, ... 10 kilos. 10 kilos. 10 kilos.

Alcohol, .... 100 litres. 100 litres. 100 litres.

Methyl or ethyl iodide, 8 kilos. 5 kilos. 20 kilos.

Caustic potash or soda, 10 u 10 kilos. 10 “

According to the patent specification of Hofmann(May 22, 1803), the following proportions may beused for violet:—1 part of magenta, 2 parts of ethyliodide, and 2 of methylic or ethylic alcohol.

Ethyl iodide does not give the bluer shades soreadily as methyl iodide; hence, for the B B colourmethyl iodide only is usually employed. If, however,methylic alcohol be employed together with methyliodide, methyl iodide and ethylic alcohol are formed;thus—

CII 3 .OH + C„H 5 I = C 2 II s .OH + CH 3 I .

So that blue shades may bo obtained with methyliodide if wood spirit, or even ordinary methylatedspirit, be employed along with it.

If the hydriodides of the violet bases are used indyeing, it is necessary to employ alcohol as a solvent,the salts being insoluble in water. In addition, thehigh price of iodine at the present day renders itnecessary to recover the iodine ; i.e., to convert thehydriodides into other salts. For this purpose thecrude hydriodides are boiled with alcoholic causticsoda in a digester; the mass is then washed withhot water to separate sodium iodide and excess ofcaustic soda, and dissolved in hydrochloric, sulphuric,or acetic acid. From this filtered solution the dye-stuff is thrown down by common salt, and is collectedand dried. The product is perfectly soluble in coldwater if pure.

Some manufacturers employ the alcoholic bromidesin lieu of the iodides. The hydrobromide and ethylbromide of triethyl rosaniline are sometimes metwith in commerce.

As already stated, the violet B B consists chieflyof a salt of trimethyl rosaniline. In addition thesalts of the mono- and tri- methylates of trimethylrosaniline are usually present also to a small extent.Both of these are violet blue dyes.

Some few dyes have likewise been prepared byprocesses similar to those used for making Hof-mann’s violets. Methylated and ethylated mauvani-lines are thus prepared from mauvaniline; benzylchloride violets from rosaniline and benzyl chloride ;benzyl-methyl violet from Hofmann’s violet R andbenzyl chloride ; phenyl-methyl violet from violet deLyons and methyl iodide ; and isopropyl, amyl, allyl,and other analogous violets from isopropyl, amyl,allyl, &c., iodides, and rosaniline.

Turpentine Violet (Britannia Violet ).—The reaction employed by Perkin in the production of this violethas been used in the preparation of other analogousproducts. Turpentine is dropped into bromine water,and the whole shaken together till no free bromineis left. One part of the brominated turpentine, 1of rosaniline, and 6 of wood spirit or alcohol, are thenheated in an enamelled autoclave for eight hours to

140° to 150° C. After cooling, the product is dis-