360 Dr. Schunck on Rubian and its Products of Decomposition 



An excess of 0'6 per cent, of hydrogen, as this formula would 

 pre-suppose, is unusually large ; an excess of 04 per cent, of 

 carbon is seldom or never obtained in the analysis of a pure sub- 

 stance. The most common impurity of alizarine is verantine ; 

 and since the latter contains, as I shall presently show, more 

 oxygen for the same amount of carbon and hydrogen, it follows 

 that if a portion of it be mixed with the alizarine, the amount of 

 carbon and hydrogen in the latter will be reduced, and the com- 

 position will approximate to that given by Wolff and Strecker. 



Again, if the correct formula for alizarine be C 20 H 6 O 6 , the 

 formula of rubian must necessarily be C 20 H 11 O u , which re- 

 quires in 100 parts — 



Carbon 5479 



Hydrogen 5 02 



Oxygen 40- 19 



These numbers, as will be perceived, do not agree so well with 

 those of the analyses as those corresponding to the formula 

 which I have given above. The lead compound of rubian can, 

 under this supposition, only be represented by the formula 

 6(C 20 H n O n ) + 13PbO, which requires in 100 parts- 

 Carbon 26-03 



Hydrogen 2 - 38 



Oxygen 19-10 



Oxide of lead .... 52-49 

 Here also it will be seen there is less accordance with the 

 numbers found by experiment than in the case of the other 

 formula. But besides this, the latter formula is of too compli- 

 cated a nature to be received ; I therefore consider the formula 

 C 14 H 5 O 4 , or perhaps C 28 H 10 O 8 , for alizarine to be as firmly 

 established as it can be with the means at present at our com- 

 mand. 



Verantine. — This substance coincides in most of its properties 

 with the substance to which I formerly gave the name of the 

 beta-resin of madder. When prepared according to the method 

 above described, it is obtained in the shape of a reddish-brown 

 powder, similar in colour to snuff or roasted coffee. It has the 

 following properties. When heated on platinum-foil it melts and 

 then burns away without leaving any residue. When heated in 

 a glass tube it gives a small quantity of an oily sublimate with- 

 out a trace of anything crystalline. When however it contains 

 alizarine, as it very often does, it gives on being heated a cry- 

 stalline sublimate., consisting of the latter substance. It dissolves 

 in concentrated sulphuric acid with a brown colour, and is re- 

 precipitated by water in brown flocks. On heating the solution 

 in concentrated sulphuric acid it becomes black, sulphurous acid 



