136 Dr. Schunck on the Colouring Matters of Madder. 



until nothing more is dissolved by the alcohol. The boiling alcohol, 

 after being filtered, deposits on cooling rubiacin in small shining 

 yellow crystals, which must be purified by recrystallization. The 

 fluid has a yellowish-red colour. On evaporation it gives a quantity 

 of an easily fusible dark reddish-brown fat, which by repeated fusion 

 in boiling water and agitation with the fluid while in a melted state, 

 may be separated from the rubiacin which adheres to it. The ru- 

 biacic acid which is left by the boiling alcohol is treated with a weak 

 boiling solution of carbonate of potash, in which it dissolves with a 

 dark brown colour. The solution after cooling and standing some 

 time deposits a mass of brick-red needle-shaped crystals of rubiacate 

 of potash, which are easily purified by recrystallization. By dissol- 

 ving this salt in boiling water and adding any strong acid, rubiacic 

 acid in a state of purity is precipitated as a bright lemon-yellow 

 powder. The dark solution from which the rubiacate of potash has 

 crystallized contains a quantity of the brown fat dissolved in the 

 potash. 



The brown substance left undissolved by the perchloride or per- 

 nitrate of iron is, as I stated above, a compound of one of the two 

 fats with oxide of iron. On being treated with muriatic acid the 

 oxide of iron is dissolved, leaving behind the fat, which, after being 

 washed with water, is dissolved in boiling alcohol. From this it is 

 deposited on cooling as a light brown powder. 



I mentioned above that the residue which is left on treating the 

 brown precipitate with boiling alcohol, consists principally of pectic 

 acid. It is treated with boiling water until nothing more is dis- 

 solved. The solution, which has a light brown colour, and is some- 

 what mucilaginous, gives a brown, transparent substance, which 

 easily separates in scales from the sides and bottom of the vessel. 

 After treating the residue with water until nothing more is dissolved, 

 there still remains a dark brown substance undissolved, which I 

 suppose to be a compound of some of the preceding substances with 

 oxide of iron, as it leaves a considerable quantity of ash, consisting 

 of peroxide of iron, on being burnt. 



To the aqueous extract of madder, in which the brown precipi- 

 tate had been produced by oxalic acid, I added chalk until all the 

 excess of acid was saturated, and after filtration I evaporated it. It 

 left a dark brown syrup, which may be separated by means of 

 alcohol into two substances. That which is dissolved seems to be 

 grape-sugar, and that which is left behind is a species of extractive 

 matter, which agrees in its properties with xanthin, as described by 

 Kuhlrnann. It has a brown colour. During evaporation in contact 

 with the air it deposits a brown substance or apothegma, like all ex- 

 tractive matters. But it is distinguished from all other extractive 

 matters which I know, by being converted into a green insoluble 

 substance when its solution is boiled with dilute sulphuric or mu- 

 riatic acid. I have not examined it further, but I may mention that 

 it is probably this body which exerts such a deleterious influence 

 during the process of madder-dyeing, rendering the red and purple 

 brown and unsightly. 



