DYEING AND CALICO PRINTING.

268

diaphragms ; this cylinder receives steam (is in communication with the vesself by means of the tube containing the stopcock A), d, another cylinder, servingas envelope for the last mentioned, and also in communication with f by meansof a tube fitted with the stopcock l, which on being opened admits steam to d,the excess of which escapes by m. h, condensing apparatus, into which theproducts of the distillation are admitted by means of the tube/, which com-municates with c c. When the furnace for superheating the steam has beenheated to 360°, steam from the boiler at 180 0 (= 10 atmospheres, or 150 lbs.pressure to the square inch) is admitted into the cylinder d, and as soon as thecylinder c c and its contents have acquired that temperature the stopcock k isopened, by means of which superheated steam is admitted, first at a tempera-ture of 200 0 , increasing gradually to 220°, 230°, and at last to 240°. Thealizarin is volatilised, and carried by the steam in the shape of an orange-yellow coloured gas, which on condensing exhibits a powder of the samecolour. When the operation is finished this powder is collected on a filter,while the condensed steam can be applied for dyeing purposes.

Fig. 21.

B Iff

KiiliS

'_'

_|

B9 , '!Sr

rwimfunV. ;

mmm

JSSRt^'

Irwli

Madder lakes are insoluble combinations of the red colouring matters ofmadder with certain metallic oxides. Some of these are of great beauty, andemployed by artists as oil and water colours, and they may be fixed upon textilefabrics, by the intervention of albumen, in the same manner as ultramarine,or they may be applied by being dissolved in a proper vehicle, say acetic acid,and thus used for calico-printing, because on expelling the solvent by steamingthe pigment is fixed.

The Only madder lakes which have obtained extensive application are thoseof alumina, the alizarate and purpurate. They are a more or less deep rose,with a slight—yet distinct and very characteristic—bluish hue. It is not easyto obtain really deep red coloured madder lakes in a dry state, owing to thegreat difficulty of obtaining alumina free from iron. These pigments yieldfast colours, and are on that account esteemed in calico-printing. The prin-ciple of the preparation of these substances is that the madder pigments aredissolved by alum solutions, and precipitated by means of carbonate of soda.The following is M. Persoz’s process:—Madder is washed with cold water