228 ANILINE ANI) ANILINE DYES. —Manufacture of Violaniline, Mauvaniline, &c.

sulphurous or sulphuric acid, should be employed;the rosaniline should be itself well crystallized, or atany rate prepared from a salt several times crystal-lized, and perfectly dry and in fine powder: it mustbe free from every trace of excess of fixed alkali usedas precipitant. 100 parts of rosaniline are placed inan enamelled iron pan, and 20 of the glacial acidadded little by little with continual stirring; themass may be heated to 60° or 70° C. with advantage,but care must be taken that the acid does not distilover. When thoroughly incorporated, 240-250 partsof boiling water, free from calcareous salts, is rapidlyadded, the whole boiled a few minutes (but not long,otherwise the acetate is partially decomposed, anuncrystallizable basic salt being formed), and thenrun into crystallizing pans. After two or three daysfine crystals are obtained, the weight of which isabout equal to that of the rosaniline used.

It is possible to prepare the acetate by doubledecomposition of the sulphate, arseniate, &c., by leadacetate; but the resulting salt is less finely crystallized.The insoluble lead compound retains a considerableamount of colouring matter, and the yield is greatlydiminished.

The sulphate of rosaniline may be prepared in thesame way as the hydrochloride, substituting, how-ever, sulphuric for hydrochloric acid if method No.1 be used, or sulphate of soda for common salt ifmethod No. 2 be employed; or it maybe preparedby adding sulphuric acid in just the right quantityto the crude rosaniline prepared by method No. 3,and crystallizing the salt. In this case, or when thevariation is adopted of adding the acid to the boilingsolution of the base in lime or baryta water, theliquor must be kept hot by the injection of steam,and must be again filtered to separate sulphate oflime or baryta. The quantity of acid requisite isknown by calculating the amount equivalent to thelime or baryta used in the boiling process.

The oxalate is prepared in precisely the same wayfrom oxalic acid, and the lime water solution ofrosaniline obtained by method No. 3, or prepared byheating a purified (recrystallized) aniline salt withlime in excess, and boiling with water under pressure.

Utilization of Fuchsine Residues .—In the prepara-tion of fuchsine by the arsenic process, various kindsof residues and bye products are obtained, the natureof which vary with the modification of the processused; With the lime process (method No. 3) a mudis left consisting of the arseniate and arsenite ofcalcium,* humus-like decomposition products, viol-aniline, mauvaniline, &c., and mother liquors con-taining chrysotoluidine amongst other products. Bythe other two processes, an insoluble mass of hydro-chlorides of violaniline, mauvaniline, &c., mixed withhumus-like products, is formed, together with arsenicalmother liquors.

Processes have been proposed for the recovery ofarsenic from these residues, but as yet these methodshave been but little employed. Thus Tabourin and

* The latter salt usually contains but a small fraction of thetotal arsenic present, calcium arsenite being more soluble inwater than the arseniate (Brinmeyii).

Lemaiiie burnt the dried solid residues, leading theevolved gases through cooling pipes and chambersto condense the arsenic. The concentrated arsenicalliquors were solidified by addition of quicklime, andthe mass heated with carbon; the evolved arsenicvapours being burnt to white arsenic, and condensedas before. Weaker liquors were treated with milkof lime, and manganese chloride solution, to reducearsenic acid to arsenious; the precipitated calciumarsenite was then treated as before.

Randu & Co. calcined the residues, collectingarsenious oxide in flues, &c.; or they calcined withcoke dust, collecting metallic arsenic.

The arsenical liquors obtained by methods 1 and2 are frequently evaporated until sodium chloride“salts out,” for the most part in crystals. Nitricacid may then be added to oxidize arsenite present,and finally the resulting arseniate of soda crystallized,and sold to the calico-printer as “ dunging salts.”

Another method of treatment is to evaporate toa small bulk, and then distil with sulphuric acid.Chloride of arsenic passes over, and can be oxidizedto arsenic acid by passing a current of chlorine gasthrough its aqueous solution.

Or again, the liquors are evaporated to a third oftheir volume; and as much sulphuric or hydrochloricacid added as corresponds to the neutral sodiumarsenite present. Sodium sulphate or chloride crys-tallizes out, and from the filtrate an impure arsenicacid is regained, which may be used over again.

A better method of regaining the arsenic acidfrom these liquors is to add calcium chloride solutionor milk of lime, or both, so as to obtain a precipitateof calcium arsenite and arseniate; this is then washedand treated with sulphuric acid, mixed with a littlenitric. Sulphate of calcium is formed and free arsenicacid, the arsenious acid being reoxidized by the nitricacid. By evaporation and decanting from the gypsumdeposited, a solution of arsenic acid is obtained, whichmay be used over again as a fuchsine-making agent.The lime or baryta mud obtained by method 3 maybe directly treated in this way.

Mother liquors and weak liquors containing onlya small quantity of colouring matter are most eco-nomically utilized by precipitating the colouringmatter as a lake, which is then dried and sold as apigment. Tannin, alumina, and stannic oxide formhighly insoluble compounds with rosaniline, and areused for this purpose.

Manufacture of Violaniline , Mauvaniline, andChrysotoluidine .—Though not red dyes, these bodiesmay be considered here, since they are obtained asbye products of the fuchsine manufacture. Itusually happens that the fuchsine residue still containsrosaniline, from two to three hundredths being theusual amount with careful manufacture; but whenthe extraction process is not properly managed 4 or5 per cent, may be left in the residue. The quantityof humus-like product formed depends much on theway in which the “ melt” is manufactured. It seemsto be formed chiefly at the expense of violaniline; iftoo high a temperature has been reached during thefusion (above 200° or 210° C.), other alteration or