23 6

DYEING AND CALICO PRINTING.

Bucholz found in ioo parts of air-dried madder—

Red extra&ive matter .

Brownish red matter soluble in alkalies and

alcohol .

Acrid extractive matter.

Red fatty resin.

Brownish red gum.

Woody fibre .

Matter soluble in caustic potash.

Vegetable salts of lime.

Moisture.

Loss.

39 '°°

i*og

0*06

I'02

g*oo

22-05

4*o6

i*o8

I2'00

7*04

According to John, 99 parts contain—

Brown-red wax-like substance .

Red resin.

Red extractive matter .

Oxidised extractive.

Brown gum .

Woody fibre .

Acetates of potassa and lime .

Phosphate, sulphate, and chloride of

potassium.

Phosphate of lime and magnesia.

Silica.

Oxide of iron.

100*00

roo

3*oo

12-00

5*00

8’oo

42-05

8 - oo

7*00

7*05

1*05

0-05

The varieties of madder from different localities behave in the dye-beck ina perceptibly different manner. This appears partly due to the special natureof the colouring matter contained in each variety. It is, therefore, useful tostudy each kind separately. Since there is on this subject wide divergenceof opinion both among scientific and practical men, we premise the followingprinciples :—1. The fresh root contains its tinctorial principles in anotherform from the ground madder which has been kept for some months. In theformer state the colouring matters are in some combination which rendersthem soluble in water, but the moment the juice of the root is in contact withthe air this state is modified. 2. The soluble combination of the madder-pigments is of the same kind as those which chemists know under the nameof glucosides. The experiments made by E. Koechlin, Decaisne, Watt,Robiquet, Colin, Kuhlmann, Higgin, and Runge, fully prove the existence ofsoluble colourable* matters in the fresh root as well as in the powder metwith in commerce, though the quantity decreases with the increasing age ofthe madder, t The researches of these chemists throw no light upon the precisenature of these substances. We shall review the labours of the authoritiesnamed, and compare them with the results of Schunck and Rochleder. Watt,while operating upon Zealand madder, observed that cold water takes up

* Such as are under certain circumstances capable of forming pigments and dyes,t No satisfactory explanation has been given for the well-known faCt that madder improvesin the cask. This is most marked in Zealand madder, which reaches its perfection aftertwenty months, and is still excellent after thirty-two. Avignon madder is spoiled much earlier.