MADDER. 925 



three inches in breadth is dipt into the infusion, allowed to dry 

 and the dipping repeated ; or the infusion may be applied to 

 one side only of thin and sized drawing paper. For red paper, the 

 infusion of litmus is acidulated slightly by means of acetic acid. 

 A paper prepared from an infusion of the best cudbear without 

 the addition of either alkali or acid has a purple colour and is 

 affected by both acids and alkalies. It is convenient in alkali- 

 metry,, being already too red to be sensibly affected by carbonic 

 acid, while it is distinctly reddened by the mineral acids. The 

 colours from the lichens are beautiful, but fugitive ; they are 

 chiefly employed by the dyer to give a bloom to more fixed 

 colours. 



COLOURING MATTERS OF MADDER. 



Alizarin? C 37 H 12 O 10 (Robiquet). This is a crystalline matter 

 of a red colour which was extracted by MM. Robiquet and 

 Colin from the ground roots of madder, the Rubia tinctorum. 

 To concentrated sulphuric acid an equal quantity of ground 

 madder is added in a gradual manner, so as to prevent any 

 sensible elevation of temperature ; in two or three days nearly 

 all the constituents of the madder are charred and destroyed 

 except the alizarin. The acid is then washed out from the 

 black mass, which is dried and digested with portions of cold 

 alcohol, to take up a fatty matter it contains. The alizarin is 

 afterwards dissolved out by boiling alcohol, the latter solution 

 mixed with water, the alcohol distilled off, and the alizarin 

 which has precipitated is collected on a filter.f It is a red 

 powder, which may be sublimed and is obtained in long flexible 

 capillary needles, having an orange colour; but unless the sub- 

 liming vessels be very low and flat, almost the whole of the 

 alizarin is decomposed. Alizarin is somewhat soluble in boiling 

 water to which it communicates arose colour; at 54, it dis- 

 solves in 212 parts of alcohol and in 160 parts of ether. It 

 has a decided affinity for some animal matters, being soluble in 

 albumen, and is precipitated in combination with the latter 

 when coagulated. Phosphate of lime appears also to combine 

 with the colouring matter of madder, from the well known fact 



* From alizari the name applied to madder roots in the Levant. 

 t Annales de Chimie et de Physique, tome 34, p. 228 j and Journal de Phar- 

 macia, tome 21, p. Mi)2. 



