112 Chemical Manufactures. 



rieties of orange and brown. It is not used in dyeing silk. 

 The splendid colour termed Adrianople or Tui*key red, is pro- 

 duced with it by a very complicated process, which is practised 

 on a large scale in France, and is considered there an industry 

 of the highest importance. 



It was formerly supposed that madder contains only a red 

 and a tawny colouring matter ; but it has been ascertained that 

 it includes two reds, termed respectively by their discoverer 

 alizarine and purjmrine. It contains other colouring matters 

 also, including two that are resinous, with sugar, acids, etc. If 

 an acid is added to the brown muddy liquor, which results on 

 treating madder with boiling water, a complicated precipitate 

 is thrown down. When boiling water will extract no more 

 colouring matter from madder, it will give out a large ad- 

 ditional quantity if acted on with an acid, then washed, and 

 treated with caustic alkali ; and a precipitate may be thrown 

 down as before by means of an acid. Nothing will then re- 

 main but woody fibre. Alizarine, or madder red, is found 

 among the substances precipitated by the acid. It is always 

 present in the madder of commerce, but is not to be discovered 

 in the roots when first taken out of the ground. The cells of 

 the living plant contain only a transparent yellow juice, which 

 becomes red by exposure to the atmosphere, and has been 

 termed Rubian. It is believed to be identical with the bitter 

 principle, and, by means of an acid, to be convertible into dif- 

 ferent dyeing substances. If madder is treated with cold 

 water, and the liquid is allowed to stand in a warm place, it 

 loses its bitterness and yellow tinge, and gelatinizes ; it is then 

 capable of producing the most brilliant colours. The whole 

 tinctorial effect of madder is not developed until the process of 

 dyeing, when the gradual heat first applied causes the required 

 fermentation of the rubian. 



If the gelatinized cold solution is treated with alcohol, and 

 the alcoholic solution is evaporated, a further heating will sub- 

 lime alizarine in long brilliant transparent orange-coloured 

 crystals. Alizarine may be obtained also by heating madder 

 itself; but the product will be rendered impure by an empy- 

 reumatic oil. Although alizarine is of a reddish-yellow colour, 

 its compounds are a beautiful purple or violet hue. It is 

 precipitated from their solutions by metallic salts, etc., if in 

 combination with the fixed alkalies ; but spontaneously by the 

 escape of the ammonia, if in combination with that alkali. Ali- 

 zarine is dissolved without change by boiling concentrated sul- 

 phuric acid, and is set free from the solution by the addition 

 of water. It has a very strong affinity for alumina ; but if, in 

 dyeing with it, bases are present, they will enter into combina- 

 tion with it ; if acids, they will combine with the mordants. 



