Alizarin plays the principal, and probably the only part, in the pro duction of madder colours. Schunk has, in fact, after a long course of experiments, been led to the conclusion, that the final result of dyeing with madder and Be preparations is simply the combination of alizarin with the various mordants employed, and that consequently If an economical method of preparing alizarin on a large scale could be discovered, a great gain would result to the arts.
2. Purpurin was the name given by Robiquet and Colin to tho colouring matter that remained dissolved in the alum liquor after the preparation of alizarin. Dr. Debue has called it oxylizaric add. It dissolve, in alkalies with a red colour, quite distinct from the purple of an alkaline solution of alizarin, and moreover the resulting solution decomposes when exposed to the air, which is not the case with a similar solution of alizarin. Professor Stokes, who has examined the optical properties of purpurin, also thinks it quite distinct from alizarin ; nevertheless, these two bodies aro shown, by other re-actions, to be closely allied substances. Further research will probably remove all doubt concerning them.
3. flubiacin (C„Ii„0,„). This body is one of several yellow colouring matters contained in madder. It was first noticed by Runge, who called it Madder-orange. Schunk has obtained it in acieular and lamellar crystals. It gives red compounds with bases, but does not contribute to the production of fast colours during the process of madder dyeing ; Schunk thinks that it even acts injuriously. Persalts of iron convert it into rubiacic add a lemon yellow, non crystalline powder. Rubiacate of potash crystallises from water in long, silky. brick-red needles.
Rubiacin is soluble in strong sulphuric acid, and hence is found in the acid liquor mentioned when treating of the preparation of alizarin.
4. Chlorogenin.—Kuhlman, by treating garancin with boiling alcohol, evaporating to dryness, dissolving in water, precipitating with acetate of lead and baryta water, and treating the precipitate with dilute sulphuric acid, isolated a body that he called xanthin. Schunk, however, shows that this body is a mixture of rubian and an extractive matter to which he has given the name chlorogenin, the rubichloric add of Rochleder. Its aqueous solution becomes brown when exposed to the air, and hence the uniform dirty reddish-brown tint which a piece of calico exhibits after having been dyed with madder. In the manu facture of garancin. the chlorogenin is mostly decomposed and removed. The effect of adding lime to a dye-bath is partly, according to Schunk, to take away the chlorogenin, rubiacin, and other valueless and injurious bodies from their aluminous combination.
5. Erythrozynt is the name given by Schunk to an azotised body existing in madder. It acts as a ferment, and bears the same rela tion to rubian that emulsin does to amygdalin. It is the ferment peculiar to madder, or rather to rubian, the latter body not yielding alizarin when brought in contact with other ferments. It contains very little more than 4 per cent of nitrogen. It may be obtained from
madder by digesting the latter in water at 100° Fahr., and precipitating the aqueous extract with alcohol.
6. Rubian Madder is extracted with boiling water, the extract agitated with animal charcoal, and the latter digested in alcohol. A solution is thus obtained which leaves on evaporation a nearly pure substance, to which Schunk has given the name of rubian. It is an amorphous, gum-like mass, of deep yellow colour, intensely bitter taste, and soluble in water and alcohol. By the action of various agents it is broken up into grape sugar and alizarin, together with 7. Rubiretin, and 8. Verantin ; the latter substance being accompanied by 9. Rubsafin, 10. Rubiagin, 11. Rubianin, and 12. Rubiadin, according to the reagent employed, as seen in the following table 7. Rubiretin and 8. Verantin are amorphous, resinous, and of brown colour. Along with alizarin they form the part insoluble in cold water when rubian is acted upon by either of the agents named. Rubiretin is easily soluble in alcohol : verantin less soluble in that liquid.
9. Rubutfin accompanies the last-named bodies when the splitting up is effected by erythrozym. When treated with perchloride of iron it passes, like rubiacin, into rubiacic acid. It crystallises in yellow shining needles.
10. Rubiagin accompanies rubiafin. It seems to be a distinct sub stance, but Dr. Schunk has not yet obtained it in a state of purity.
11. Rubianin accompanies alizarin, rubiretin, and verantin, when rubian is decomposed by acids. It is tolerably soluble in boiling water, and crystallises in lemon-yellow silky needles.
12. Rubiadin This body is associated with the other three when rubian is acted upon by alkalies. It crystallises in beautiful golden-yellow scales, insoluble in water, soluble in alcohol, and is com pletely volatilised by heat.
13. Chlororubian When exposed to the action of chlorine, rubian is converted into a crystallisable substance, called by Schunk Cidororubian. It is insoluble in water, but soluble in alcohol, It is formed from rubian by the elimination of one atom of sugar, and the replacement of an atom of hydrogen by one of chlorine. By the continued action of chlorine it is converted into Perchlororubiau (C..fl„C1.0,.). By the action of acids upon chlororubian a second atom of sugar is set free, and Chlororubiadin is formed.
14. Rubianic acid (Ruberythrtc acid, Rochlcder.) This acid results from the action of alkalies and oxygen upon rubian ; a vessel to which the air can have access being therefore used in its pre paration. It gives definite crystalline compounds with the alkalies, is tolerably soluble in boiling water, and crystallises in lemon-yellor% silky needles. By decomposition it yields one atom of alizarin, and twc of grape sugar.
Madder-dyeing. The colouring matters of madder have but little 6ffinity for cotton fibre, but a great affinity for mordants ; hence, vhen a pattern has been printed on cotton with a mordant [CALICO