ANILINE AND ANILINE DYES.— Manufacture of Fuciisine. 225
close upon 182° C.), was not the best material tooperate on; an oil distilling for the most part be-tween 185° and 200° C. being more suitable. Until
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Hofmann’s researches had cleared up the compositionof fuchsine, tiie raison d'etre for this was unknown,although the fact was certain.
The improved method employed at the presentday is thus described by Girard and De Laire.Into a retort holding about 2500 litres are introducedsuccessively 800 kilos, of aniline oil(either prepared by partial fractionaldistillation of benzol, so as to pro-duce directly a suitable aniline, or bymixture of various kinds of anilineoil, so as to obtain an oil of suitablecomposition), and 1366 kilos, of acid,containing 72 per cent, arsenic anhy-dride (this solution will not solidifyeven in the winter). An agitatormoved by steam is provided, the axleof which is hollow, so that steam canbe admitted to the bottom of theretort through the spindle of the agi-tator itself. In the base of theretort are two doors for with-drawing the finished charge, and at the top a safetyvalve, and a tap connected by a pipe with a tank ofhot water. Fig. 3 indicates the general dispositionof the apparatus:— a, a, the body of the retort; It, b,the dome; c, the hollow axle of the agitator; d, d,the serrated arms of agitator, to prevent the materialVOL. i.
from sticking to the bottom of the retort; e, thesteam tube; f the manhole; g, g, openings for with-drawing the charge; h, h, hot-air flues for heating theretort: these can bo opened so as to cool the retortin case of necessity. The neck communicating withthe condensing worm is on the other side of theapparatus, and is not shown in the section.
The retort is heated by hot-air flues, and is pro-vided with a good condensing worm to condense theaniline and water that pass over; the temperatureshould not rise above 190°-200° C. In from eightto ten hours the operation is completed, the progressbeing judged by measuring the bulk of the condensedliquor. This should amount to about 850 litres, andafter saturation with salt about 440 kilos, of anilineand 410 litres of water should be obtained. When800 litres of distillate have passed, and the operationis nearly finished, the fire is withdrawn, the residualheat of tiie furnace being sufficient to finish thedistillation of the unchanged aniline. To separatethe last traces steam is blown through the “melt”in the still, which mechanically carries over the lastportion of the aniline vapour. A small quantity ofhot water is then run in, and then more in smallquantities at a time; heat may bo reapplied to theretort to facilitate the “ hydration” process. At theend of about au hour a homogeneous fluid mass isobtained, which is run off through the openings intothe solution-vats for the next operation.
By this process great economy in labour, fuel, andcost is effected; and in addition, the operation ofpulverizing the cake of solidified melt is avoided, sothat the workmen are in no way exposed to thechance of inhaling arsenical dust, or to the otherpainful consequences produced by the local action ofsolid arsenical matters (sores, ulcerations, &c.) Fourmen can thus work off 2000 kilos, of crude material perdiem, and of these three are only required at the begin-ning and end of the operation; by the older processesten men are required to turn out as much material.
In many factories, instead of admitting steam at
the end of the operation to distil off the last traces ofaniline, and running in hot water to avoid the pro-duction of a solid cake, the “melt” is run out on tocooling plates, placed under a hood to carry off theaniline vapour. The cake is then transferred to aboiler provided with an agitator, Fig. 4. a, n, is the
29
Fig. 4.
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