252

DYEING AND CALICO PRINTING.

this compound differs from the corresponding alizarin lake. Mordanted clothscarcely takes any colour if immersed in a boiling rubiacin bath. Rubiacicacid is re-converted into rubiacin by the adion of sulphuretted hydrogen. Inmany of its properties rubiacin approaches purpuroxanthin as obtained bythe redudion of purpurin. According to Schunck, rubiafin, when aded uponby the per-salts of iron, yields rubiacin. Since rubiafin = C 20 H I 606 , it willlose by oxidation 4 atoms of hydrogen, becoming C 20 H I2 06.

The following is a summary conspedus of the colours of madder:—Original Colours Soluble in Water.

Glucosides , which by the adtion of acids, alkalies, and ferments are splitup into sugar and colours, insoluble in water.

Rubian (Schunck). Amorphous,.bitter, very soluble, precipitable by poroussubstances. A mixture of several glucosides.

Rtiberytkric Acid (Rochleder). Crystallisable, alizaric glucoside, con-vertible only into alizarin and sugar.

Colouring Matters, the Existence of which cannot be Doubted.

Insoluble colouring matters, due to the splitting up of the glucosides, andpresent in the ground madder of commerce.

1. Alizarin. Readily sublimable without decomposition, orange-red,crystallises in needles; yields in dyeing and printing very fast and beautifulcolours, which resist the clearing operations.

2. Purpurin. Sublimable with partial decomposition ; red, crystallises inneedles; yields in dyeing shades not quite fast, but which stand clearingmoderately.

3. Orange Matter. Crystallises in granular scales, very soluble in alcohol;yields on sublimation purpurin, but leaves a large deposit of carbonaceousmatter. Behaves like purpurin in dyeing.

4. Pseudopurptirin. Brick-red ; insoluble in alcohol, soluble in boilingbenzol, and deposited, on cooling, in crystalline needles ; decomposed by heat,yielding a very small sublimate of purpurin. Gives with mordanted cloth thesame shades as purpurin, but none of these stand clearing.

5. Purpuroxanthin, or xanthopurpurin. Yellow, crystalline, sublimable,formed by the redudion of purpurin.

Colouring Matters of Doubtful Existence,, or which Require Further

Investigation.. .

Yellow matters. —Rubianin, rubialin, rubiazin, rubiadin, rubiacin, rubiacicacid.

Resinous matters. —Verantin and rubiretin.

Commercial Producfts or Derivatives from Madder.

The madder of commerce yields, when properly treated, beautiful andexceedingly fast colours with alumina and iron mordants. Care must betaken to submit the dyed fabric afterwards to a series of operations known asclearing ( avivage). But madder is in many respeds inconvenient as a dye,this defed being chiefly, if not entirely, due to the presence of foreignsubstances along with the colouring principles. When the previouslymordanted, or printed fabrics leave the dye-beck, the red, rose, and violet