DYEING. 397 



purple crystals, by rapid heating. By removing the 

 oxygen absorbed in its production, the original color- 

 less juice may be, as it were, reproduced from commer- 

 cial indigo. This object is effected by the use of pro- 

 tosulphate of iron, which is converted into sulphate of 

 the peroxide in the process. Caustic lime is at the 

 same time added to dissolve the deoxidized indigo. 

 The colorless solution is employed in dyeing ; cloth im- 

 pregnated with it becomes blue on exposure to the 

 air. A solution of indigo in concentrated sulphuric 

 acid is also employed in dyeing. 



Wh,at is mad- 994. MADDER. Madder is the ground 

 der? roo t O f t^ rulia tinctoriutn. This plant 



is cultivated extensively in India and Europe. It con- 

 tains a red dye, produced by the action of the 'air or 

 certain chemical agents, upon the juices of the recent 

 plant. This body is called alizarine, and may be ob- 

 tained in beautiful crystals. An infusion of the root in 

 hot water contains a portion of this substance in solution. 

 What is log- 995. LOGWOOD. This is a red wood, 

 wood? obtained from Spanish America and much 



employed in dyeing. Its coloring matter is called he- 

 matoxyline. By evaporating a decoction of the wood 

 and re-dissolving in alcohol, this substance may be ob- 

 tained, on a second evaporation, in the form of yellow 

 crystals. 



DYEING. 

 996. DYEING. Few dves can be per- 



Explain the * 



theory of dye- manently imparted to cloth without the in- 



ing fast colors. tervention Q f some third su bstance, which 



