MR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOMPOSITION. 449 
purple solution, after being treated in the manner before described, there were ob- 
tained some beautiful dark yellow crystals of alizarine, which on analysis yielded the 
following result : — 
0 ' 1270 grm., dried at 100° C., gave 0*3245 carbonic acid, equivalent to 69*68 per 
cent, of carbon. 
It appears therefore that alizarine cannot be separated from the last portions of 
impurity by recrystallization merely. 
Were the above formula the correct one, it would be difficult to account for the 
circumstance that the purer the substance the greater is the excess, not only of hydro- 
gen, but also of carbon. An excess of 0*6 per cent, of hydrogen, as this formula would 
pre-suppose, is unusually large ; an excess of 0*4 per cent, of carbon seldom or never 
obtained in the analysis of a pure substance. 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 composition will approximate to that given by Wolff and Strecker. 
Again, if the correct formula for alizarine be C 20 He Og, the formula of rubian must 
necessarily be C 20 Hu On, which requires in 100 parts — 
Carbon 54*79 
Hydrogen 5*02 
Oxygen 40*19 
These numbers, as will be perceived, do not agree so well with those of the ana- 
lyses 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 2 o Hii Oii)+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 expe- 
riment than in the case of the other formula. But besides this, the latter formula is 
of too complicated a nature to be received ; 1 therefore consider the formula C 14 H 5 O 4 , 
or perhaps C 28 Hio Og, for alizarine to be as firmly established as it can be with the 
means at present at our command. 
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 
aecording 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 pro- 
perties. 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 sub- 
