MADDER 163 



jelly with alcohol, evaporating the alcoholic liquid to dryness, and heating the residue ; 

 and since the application of heat seemed to be an essential part of his process, it was 

 for a long time doubted whether alizarine was contained as such in madder, and was 

 not a product of decomposition of some other body. It was proved, however, by the 

 experiments of Schunck that it does in reality pre-exist in the ordinary madder of 

 commerce, though not in the fresh root when just taken out of the ground. It has 

 the following properties : It crystallises in long, transparent, lustrous, yellowish-red 

 needles. These needles when heated to 212 F. lose their water of crystallisation, 

 and become opaque. At about 420 F. alizarine begins to sublime, and if carefully 

 heated may be almost entirely volatilised, only a little charcoal being left behind. 

 The sublimate obtained by collecting the_ vapours consists of long, brilliant, trans- 

 parent, orange-coloured crystals, which are pure anhydrous alizarine. If madder, or 

 any preparation or extract of madder, be heated to the same temperature, a sub- 

 limate of alizarine is also obtained, but the crystals are then generally contaminated 

 with drops of empyreumatic oil, produced by the decomposition of other constituents 

 of the root. This oily matter may, according to Kobiquet, be removed by washing 

 the crystals with a little cold alcohol. Alizarine is almost insoluble in cold water. 

 It is only slightly soluble in boiling water, and is deposited, on the solution cooling, 

 in yellow crystalline flocks. When the water contains large quantities of acid or 

 salts in solution, it dissolves very little alizarine, even on boiling. The colour of the 

 solution is yellowish when it is quite free from alkalis or alkaline earths. Alizarine 

 dissolves much more readily in alcohol and ether than in water ; the solutions have 

 a deep yellow colour. Alizarine is decomposed by chlorine, and converted into a 

 colourless product. It is also decomposed by boiling nitric acid, the product being 

 a colourless, crystallised acid, phthalic acid, the same that is formed by the action of 

 nitric acid on naphthaline. Alizarine dissolves in concentrated sulphuric acid, yield- 

 ing a yellow solution, which may bo heated to the boiling point without changing 

 colour and without any decomposition of the alizarine, which is precipitated unchanged 

 on the addition of water. Alizarine dissolves in caustic alkalis with a splendid 

 purple or violet colour, which remains unchanged on exposure of the solutions to the 

 air. The ammoniacal solution, however, loses its ammonia entirely on being left to 

 stand in an open vessel, and deposits its alizarine in the form of shining prismatic 

 crystals, or of a crystalline crust. The alkaline solutions give with solutions of limo 

 and baryta salts precipitates of a beautiful purple colour, with alumina salts a red, 

 with iron salts a purple precipitate, and with most of the salts of metallic oxides pre- 

 cipitates of various shades of purple. The affinity of alizarine for alumina is so great, 

 that if the compound of the two bodies be treated with boiling caustic potash-lye, it 

 merely changes its colour from red to piirple without being decomposed. Alizarine 

 is not more soluble in boiling alum-liquor than in boiling water. The chemical 

 formula of anhydrous alizarine is, according to the researches of Messrs. Graebe and 

 Licbermann, C"H 4 (CHO 4 ). 



If alizarine in a finely divided or, what is still better, in a freshly precipitated state, 

 be suspended in distilled water, and a piece of calico printed with alumina and 

 iron mordants of different strengths be plunged into it, the latter, on gradually 

 heating the bath, become dyed. The process is necessarily a slow one, because 

 alizarine is only slightly soluble in boiling water, and as the mordants can only 

 combine with that portion actually in solution, a constant ebullition of the liquid 

 must be kept up, in order to cause fresh portions of colouring matter to dissolve in 

 the place of that portion taken up by the mordants. A very small proportional 

 quantity of alizarine is required in order to dye very dark colours, but it is absolutely 

 necessary that the bath should contain no trace of cither acid or base, since the former 

 would combine with the mordants, and tho latter with the alizarine. When the 

 process is complete the alumina mordant will be found to have acquired various 

 shades of red, while the iron mordant will appear either black or of different shades 

 of purple, according to the strength of the mordant employed. These colours are 

 as brilliant and as permanent as those obtained from madder by means of a long and 

 complicated process. Nevertheless, the red is generally found to have more of a 

 purplish hue, and the black to bo less intense than when madder or its preparations 

 are employed. On the other hand, if one of the finer madder colours which aro 

 produced on calico, such as pink or lilac, be examined, the colours are found to con- 

 tain, in combination with tho mordants, almost pure alizarine. Hence it may be 

 inferred, that alizarine alone is required for the production of these colours, and 

 that the simple combination of this colouring matter with the mordants is the principal 

 end which is to be attained by the dyer in producing them. 



Alizarine has been obtained artificially by Messrs. Graebe and Liebennann, as a 

 derivative of anthracene or paranaphthaline, which is one of the products obtained in 

 the distillation of coal-tar. Artificial alizarine is now extensively manufactured and 



