Mr. J. Higgin on the Colouring Matters of Madder. 285 



J h 



This washed madder contains principally alizarine, with a i Uo^a^ju 

 small quantity of rubiacine. It is boiled three or four times LfY* 

 with a weak solution of alum to separate the rubiacine; it is 

 next boiled with a saturated solution of alum for a quarter of 

 an hour and filtered, and this process repeated till the madder 

 is perfectly exhausted, and has become an ash-gray ; the mixed (THf. L*fc 

 liquors are cooled to 90° F., and made sharply acid with sul- i { 



phuric acid; after several hours the alizarine will have sepa- u v", 

 rated ; the separation may be assisted by violent stirring occa- 

 sionally. The filtered precipitate may be purified in the same $&[ ^° 

 manner as rubiacine. 



Alizarine thus obtained is sparingly soluble in cold water, . 

 much more so in hot ; very soluble in alcohol and aether ; very 

 soluble in boiling alum liquor, the solution is a splendid and 

 pure pink; it does not separate much from this solution when 

 cooled, but sulphuric acid precipitates it wholly in a few hours 

 in orange flocks ; an alkali added to the alum solution throws 

 down a delicate pink lake. Alizarine is less soluble in water 

 acidulated than in pure; concentrated sulphuric acid dissolves 

 it with a fine red colour; the solution may be strongly heated 

 without decomposition; addition of water precipitates it wholly 

 from the solution. Alizarine dissolved in alcohol, and lime- 

 water added, is thrown down as a dark red compound of ali- 

 zarine and lime, which is soluble to a small extent in pure 

 water, and may be entirely dissolved by continued washing ; 

 but the compound is totally insoluble in water containing lime. 

 Carbonate of soda dissolves alizarine; but the solution, on 

 standing, deposits purple flocks which dissolve in more water ; 

 the solution is crimson ; ammonia dissolves it very plentifully, 

 and forms a splendid pink solution ; carbonate of potash only 

 dissolves it on the application of heat. Alizarine boiled with 

 chalk dissolves some lime, and dyes the chalk red. Alizarine 

 is insoluble in any liquid containing sulphate of ammonia or 

 sulphate of potash, even if strongly alkaline by ammonia ; it 

 merely becomes a deep purple powder. This insolubility in I 

 boiling alkaline sulphate of ammonia is characteristic of ali- \ 

 zarine- When heated, alizarine fuses and sublimes. Mor- 

 danted cloth is dyed the ordinary madder shades by alizarine, 

 but much finer than those obtained by madder. 



Having described the isolated colouring matters, I will 

 endeavour to show that the action of cold or tepid water on 

 madder is attended with peculiar effects, and that by proper 

 treatment all the xanthine and the greatest part of the rubia- 

 cine may be made to disappear, the change being accompanied 

 by an increase in the tinctorial power ; and since, of the three 

 colouring matters, alizarine only can be made to dye colours, 



