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LXXIX. On Rubian and its Products of Decomposition, 

 By Edward Schunck, F.R,S. 



[Concluded from p. 436.] 



THE experiments above detailed prove that the decomposition 

 which rubian undergoes by fermentation, does not differ in 

 its general nature from that which results from the action of acids 

 or alkalies. The decomposing effect of the ferment extends like 

 that of these agents to three portions of rubian. The first por- 

 tion of rubian loses water and gives rise to the formation of 

 alizarine. The second loses water and produces rubiretine and 

 verantine in equivalent proportions. The third takes up water 

 and gives sugar and rubiafine, or it takes up 1 equiv. more of 

 water, and yields sugar and rubiagine. The rubianine produced 

 by acids, and the rubiadine formed by alkalies, give place, when 

 ferment is the decomposing agent, to rubiafine and rubiagine. 

 The rubiadipine, in consequence of the uncertainty of its nature 

 and origin, and the minute quantity in which it is formed, I 

 leave out of consideration. The relative proportion in which the 

 various products of decomposition are formed, seems to be about 

 the same in the case of ferment as when acids or alkalies are 

 employed. Alizarine is formed in the smallest quantity ; of 

 rubiretine and verantine a little more is produced, but the sugar 

 and the rubiafine and rubiagine exceed all the others in amount. 



It appears further from these experiments, that the ordinary 

 process of dyeing with madder is, in fact, mainly a process of 

 fermentation, that it consists essentially of a re-arrangement of 

 the elements of rubian induced by the action of ferment, whereby 

 a formation of colouring matter takes place, and that the pre- 

 cautions necessary to be taken in regard to the regulation of the 

 temperature in madder dyeing have reference principally to the 

 progress of the fermentation. The extraordinary rapidity with 

 which this process of fermentation is completed, is the only cir- 

 cumstance which distinguishes it from other processes of a similar 

 nature. 



A very interesting question now arises, suggested by the ana- 

 logy which must be presumed to exist between this and other 

 processes of fermentation, viz. By what means is the action of the 

 ferment on rubian either destroyed, retarded or promoted ; and 

 do not, any means exist of so modifying the action as to lead to 

 the formation of particular substances in preference to others ? 

 With the view of throwing some light on this question, I insti- 

 tuted a series of experiments, which I shall now proceed to 

 describe. 



Having taken a solution of rubian and mixed it with a quan- 

 tity of ferment sufficiently large to effect its decomposition under 



