Dr. Schunck on Rubian and its Products of Decomposition, 511 



lies are employed is one of the results of the process, and that 

 yeast exerts no decomposing power on rubian whatever. Hence 

 it necessarily follows, that if the purpurine of Wolff and Strecker 

 be not found as such among the products of the fermentation of 

 rubian, it must consist of a mixture of two or more o^ those 

 products. 



Now I have mentioned in the first part of this paper, that 

 though alizarine and verantine are both perfectly insoluble in 

 boiling alum liquor when acted on separately, yet that when a 

 mixture of both is employed, the mixture is found to be soluble 

 in alum liquor with the colour characteristic of purpurine. 

 Hence I concluded that purpurine is in fact a mixture of those 

 two substances, a view with which all that is mentioned regard- 

 ing purpurine completely coincides. I may mention incidentally, 

 that in making this experiment it is necessary to treat the veran- 

 tine with a little dilute nitric acid, in order to destroy the aliza- 

 rine which usually accompanies it, and then to remove the acid by 

 washing with water before employing it, and that it generally 

 succeeds best when a large excess of alizarine is used. 



To this synthetical proof of the opinion here advocated, I will 

 now add a few analytical ones. I will show, in the first place, 

 that purpurine prepared in the manner mentioned by Wolff and 

 Strecker is a substance of very variable composition, but that 

 the variations in its composition may be easily explained by 

 supposing it to consist of alizarine and verantine in different 

 proportions; and secondly, that by treatment with nitric acid 

 purpurine yields unchanged verantine and an acid, which 

 is identical with that formed by the action of nitric acid on 

 alizarine. 



In the course of my investigation I obtained at the termina- 

 tion of the process for separating the products of the fermentation 

 of rubian, an alcoholic liquid, from which the verantine had been 

 deposited, but still containing a substance, which, from its solu- 

 bility in alum liquor, would by most chemists be called purpu- 

 rine. This substance was precipitated from the solution with 

 water. Its colour was brownish-yellow. It was treated with 

 boiling alum liquor, to which it communicated a bright red 

 colour. The liquid was filtered boiling hot, and deposited on 

 cooling a quantity of red flocks. The residue was treated with 

 fresh quantities of alum liquor, until on cooling very few flocks 

 separated. A great proportion of the substance employed re- 

 mained undissolved. The flocks deposited from the alum liquor 

 were collected on a filter, and washed with water in order to 

 remove all the alum. After drying they formed a dark reddish- 

 brown powder, which was almost entirely soluble in alcohol. 

 The alcoholic solution left on evaporation a bright red mass, in 



