MADDER-LAKE. 135 



peroxide of iron, wliicli becomes blackish-purple. It is soluble 

 in sulphuric acid, and reprecipitable by water unaltered ; hence 

 its permanency when madder is charred by oil of vitriol. 

 Nitric acid, pernitrate and perchloride of iron convert it into 

 alizaric acid. Rubiacin (probably Runge's madder-orange) 

 has the formula CgjHgOjo, is slightly soluble in boiling water 

 and in sulphuric acid without decomposition ; in caustic po- 

 tassa with a purple, and in carbonated with a blood-red color ; 

 forms a dingy-red precipitate with chloride of calcium, and an 

 orange-colored compound with alumina, which last is soluble 

 in potassa with a purple color. Boiling pernitrate or chloride 

 of iron changes it to rubiacic acid. The resins are slightly 

 soluble in boiling water ; the » resin in caustic and carbonated 

 alkalies with a purple-red color, /3 resin with a dingy-red color. 

 Rubian is the bitter, nitrogenous principle. Schunck believes 

 alizarin to be the active dyeing substance in madder, although 

 he states in one place that rubiacin assists in brightening color 

 when alkali is present. He thinks that the resins impart a 

 yellowish, and xanthin a brown tone to the color. (Ann. Ch. 

 Pharm. Ixvi. 174.) 



Higgin ascribes some effect to rubiacin and xanthin in dye- 

 ing. He believes that xanthin passes by a kind of fermenta- 

 tion, first into rubiacin and then into alizarin, and that the 

 resins are products of decomposition with boiling water. 

 (Phil. Mag. (3) xxxiii. 282.) 



Residue of 3Iadder. — Wydler proposes the following method 

 of using the residue of madder, exhausted by dyeing (Schweizer 

 Gewerbebl. 1847). The pressed residue is mixed with 40 per 

 cent, oil of vitriol, the mixture steamed for an hour, and then 

 washed until the wash-water tests no longer acid. It is said 

 to yield as much color as before. 



Madder-lake. — A fine madder-lake is thus prepared from 

 an ordinary article, by Kressler. 1 oz. common madder-lake 

 is powdered, treated with 2 oz. strong acetic acid (1.045), 

 stirred frequently, set aside for 12 hours, then diluted with 

 6-8 pts. distilled water, and filtered. Twice as much boiling 

 water is added to the clear filtrate, and then gradually a dilute 



