364 Dr. Schunck on Rubian and its Products of Decomposition. 



The formula of this compound must be expressed^ in the fol- 

 lowing manner : — 



3(C 14 H 4 O 4 + CuO) + C 14 H 5 O 5 . 

 These analyses show that verantine, like many substances, the 

 acid character of which is not well-marked, combines with bases 

 in various and complicated proportions. 



It appears therefore that verantine differs from alizarine by 

 containing 1 equiv. more of oxygen. According to Debus, the 

 same relation exists between alizarine and his oxylizaric acid. 

 He gives for alizarine the formula C 30 H 10 O 9 , and for oxylizaric 

 acid C 1S H 5 O 5 , so that 2 equivs. of the latter contain 1 equiv. 

 more oxygen than 1 equiv. of the former. If my view of the 

 composition of these substances be the correct one, the relation 

 subsisting between the two is still more simple. Nevertheless 

 I have some hesitation in asserting that verantine is to be con- 

 sidered as a higher oxide of the same radical as alizarine, or in 

 supposing that it may be formed by oxidation from the latter. 

 Its formation is due, as I shall presently show, not to any pro- 

 cess of oxidation, but rather to the splitting up of an atom of 

 rubian into two bodies. 



Rubiretine. — This substance is identical with that which I for- 

 merly called the alpha-resin of madder, from which it does not 

 differ in properties. It is obtained as a dark brown, opake resin- 

 ous mass, brittle when cold, but becoming soft and almost melt- 

 ing in boiling water. On being heated to a higher degree, it 

 melts completely without being decomposed. It is generally 

 found to be mixed with a small quantity of verantine, from which 

 it may be separated by solution in cold alcohol, which leaves the 

 greatest part of the verantine behind ; 1 have however found it 

 impossible to remove the last traces of that substance. It is 

 almost insoluble in boiling water. Its solution in alcohol is dark 

 yellow. It dissolves in concentrated sulphuric acid with a yel- 

 lowish-brown colour, and is decomposed on boiling the solution 

 with blackening and disengagement of sulphurous acid. Boiling 

 nitric acid changes it into a yellow substance, which no longer 

 softens at the temperature of boiling water, and is very little 

 soluble in alcohol. It dissolves in alkaline liquids with a 

 brownish-red colour, and is reprecipitated by acids in brown 

 flocks, which on boiling the liquid cohere into dark-brown semi- 

 fluid masses. When heated in a glass tube, it usually gives a 

 small quantity of sublimed alizarine mixed with a brown oil. It 

 is not capable of dyeing when quite free from alizarine. Its 

 analysis yielded the following results : — 



I. 0*5300 grm. from the decomposition of rubian, dried at 

 100° C. and burnt with chromate of lead, gave T3190 carbonic 

 acid and # 2405 water. 



