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



still more of that substance the colour may be rendered cherry- 

 red, these colours being evidently mixtures of the violet due to 

 alizarine and the brownish-red produced by verantine. Pure 

 alizarine is not more soluble in boiling alum-liquor than in water, 

 as has been repeatedly shown; it only communicates to the 

 liquor a yellow colour, and crystallizes out again on the liquid 

 cooling. Verantine is still less soluble in alum-liquor. If this 

 substance be dissolved in caustic alkali and be then precipitated 

 with a solution of alum, the precipitate does not dissolve in the 

 least degree, however much alum be added; it only communi- 

 cates a slight yellow tinge to the liquid. If, however, a mixture 

 of alizarine and verantine be dissolved in caustic alkali and they 

 be then precipitated together by means of a solution of alum 

 added in excess, then on boiling the precipitate with the liquid, 

 a bright red solution is obtained, and on filtering and allowing 

 to cool, orange-coloured flocks are deposited, while the liquid 

 still remains red, but gives a yellow precipitate on the addition 

 of acid. By treating the residue with additional quantities of 

 alum-liquor more is dissolved with the same colour, and this 

 continues until either the alizarine or the verantine, whichever 

 of the two was present in the smallest quantity, is removed. 

 From this experiment I am inclined to conclude that alizarine 

 and verantine are capable of forming a double compound with 

 alumina soluble in boiling water, and that a mixture of the two 

 in the proportion in which they exist in this compound, consti- 

 tutes what has been called purpurine. At all events, it follows 

 that alum is not adapted as a means of separating the substances 

 derived from madder. The fact of rubianine also dissolving in 

 boiling alum-liquor and crystallizing out again on cooling, is an 

 additional objection to its use. 



The difficulty of obtaining pure verantine in sufficient quan- 

 tity for the purposes of analysis, has prevented me from deter- 

 mining its composition with the requisite accuracy. I have how- 

 ever obtained approximations sufficiently near to remove almost 

 all doubts on the question. 



I. 0-3280 grm. verantine, dried at 100° C. and burnt with 

 chromate of lead, gave 0-7865 carbonic acid and - 1215 water. 

 II. - 3220 grm. gave # 7740 carbonic acid and 0-1205 water. 



III. 0-2890 grm. gave 0-6995 carbonic acid and 0-1040 water. 



IV. 0-1255 gnn. gave 0-3010 carbonic acid. 



These numbers agree best with the following composition : — 



129 100-00 10000 10000 10000 



