ANILINE REDS. 179

this manner is sent into market without any purification, under the name“ azaleine.”

During the operation the mercuric nitrate is reduced to the metallic state.Almost the whole of the mercury can be recovered, re-converted into nitrateof mercury, and used afresh in the preparation of azaleine. The bulk of thenitric' acid can be recovered as an alkaline nitrate. Next to the arsenicalmethod, this is the most economical procedure.

Lauth and Depouilly heat 6 to 8 parts of aniline to 150°—160° C., with1 part nitrate of aniline. The fire must be removed as soon as the reactionbecomes lively, or the mass will ignite. After the expiration of several hoursa mass is obtained of a fine violet-red colour, which may be purified byboiling with 20 parts of water, when the unconverted aniline rises to thesurface of the liquid as a scum, and is removed. The solution is then filteredthrough sand, and on cooling deposits a green paste with a metallic reflection.This process yields only 7 to 8 per cent of colouring matters, and the purifi-cation is difficult.

A variety of other oxidising agents have been proposed, such as phosphateand acetate of mercury, nitrate of lead, free nitric acid, aqua-regia, nitrate ofantimony, iodine, iodide of mercury,—in faCt almost every metallic salt. Theexpense and inconvenience of most of these processes has caused them to bequietly abandoned, and prevented an immense amount of litigation. A recentproposal deserves serious attention. Aniline is heated with nitro-benzol.The yield is asserted to be very large, the process simple, and the subsequentpurification easy.

By far the largest part of the magenta of commerce is prepared by thearsenic acid process, which we shall therefore describe in some detail.

A commercial aniline is selected, containing as nearly as possible 3 parts ofaniline with 1 of toluidine, which is obtained by mixing 75 per cent ofkuphaniline and 25 per cent of baraniline: 800 kilos, of this aniline and 1370kilos, of a solution containing 72 per cent of anhydrous arsenic acid areintroduced into the apparatus (Fig. 15). The still, capable of holding2500 litres, is fitted with a stirrer, worked by steam-power. A wide tubedescends, parallel with the axis of the agitator, to the bottom of theapparatus, and serves to introduce steam. In the upper part are a man-hole,a safety-valve, and a tap in communication with a tank of hot water. Beloware two large holes for emptying. The neck of the still communicates with alarge worm, which serves to condense the aniline volatilised in the course ofthe process. The temperature should not exceed 190° to 200° C. Theoperation lasts 8 to 10 hours. When the transformation is complete, about 850litres of a mixture of aniline and water will have been condensed and col-lected, which, if separated by the addition of common salt, yield 440 kilos, ofaniline and 420 of water. When 800 litres of the mixture have passed over,the fire is withdrawn, as the apparatus will still retain heat enough for thetermination of the process and for completing the volatilisation of the freeaniline. During this time the agitator must be kept in constant motion.Steam is now allowed to enter by the descending tube, and sweeps awaymechanically the raw aniline yet remaining in the still. By degrees boilingwater is now introduced, whilst heat is again applied to the apparatus. Whenthe mass has become a homogeneous liquid, which is effected in about an

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