142 Dr. Schunck on the Colouring Matters of Madder. 



pitate; with nitrate of silver a yellow precipitate, which is not changed 

 by boiling; with protonitrate of mercury a yellow precipitate; with 

 perchloride of mercury a crystalline, yellow precipitate ; with proto- 

 chloride of tin a dirty yellow precipitate ; with perchloride of tin a 

 light yellow precipitate ; with chloride of gold a yellow precipitate, 

 not changed by boiling the fluid. 



I have analysed rubiacin, rubiacic acid, and rubiacate of potash, 

 and have obtained results which agree very well with one another. 

 These analyses give for rubiacin the formula C 3 , H,, l0 , for rubiacic 

 acid C 3 , H 9 17 , and for rubiacate of potash C 31 H 7 15 + KO. It 

 therefore appears that rubiacic acid contains seven atoms of oxygen 

 more than rubiacin, and the facility with which they may be converted 

 one into the other is easily conceivable. In rubiacate of potash 

 two atoms of water existing in rubiacic acid are replaced by one atom 

 of potash, which is not usually the case with potash salts. I do not, 

 however, consider these formulae as completely established, since I 

 was obliged, from want of material, to operate on such extremely 

 small quantities. 



Rubian. — This substance is obtained, as I mentioned above, by 

 treating the brown precipitate produced by an acid in an extract 

 of madder with cold water, after having removed the excess of acid. 

 It has the following properties : — 



In thin layers it is perfectly transparent and of a yellow colour. 

 When dry it is brittle. It is soluble in water; the solution has an 

 extremely bitter taste. A concentrated boiling solution forms a jelly 

 on cooling. It is precipitated from its aqueous solution by all acids, 

 in yellow flocks. It is decomposed by nitric acid. In the watery 

 solution lime and baryta water produce red flocculent precipitates, 

 perchloride of iron a dark reddish-brown colour, but no precipitate, 

 sugar of lead a brown flocculent precipitate, nitrate of silver a floccu- 

 lent precipitate, corrosive sublimate no precipitate, tincture of galls 

 and solution of glue no precipitates. The solution imparts a slight 

 tinge to mordanted cloth, but so slight that this substance cannot 

 be considered as a colouring matter. The solution deposits nothing 

 during evaporation at all resembling apothem, and it therefore is 

 not extractive matter. It dissolves in alcohol with a yellow colour, 

 and in alkalies with a red colour. It dissolves in concentrated sul- 

 phuric acid with a red colour ; the solution on being heated becomes 

 black, and gives off sulphurous acid. When heated on platinum 

 foil it melts, swells up immensely, and burns, leaving some ash. 

 When heated in a tube it melts and gives yellow fumes, which con- 

 dense and form a crystalline sublimate very much resembling ru- 

 biacin, so that I am induced to think that there is some relation 

 subsisting between these two substances. 



Pectic Acid. — There can hardly be a doubt, I think, that that part 

 of the brown precipitate which is insoluble in alcohol, but soluble in 

 water, is pectic acid, as will be seen from its behaviour towards re- 

 agents, which is as follows : — It is soluble in water; the solution has 

 a light yellow colour, and reddens litmus paper slightly. In the 

 watery solution acids produce white flocculent precipitates, alcohol a 



