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XXVIII. On the Constitution of the Colouring Matters of Madder, 

 By Edward Schunck, F.R.S. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



IN the Annates de Chimie et de Physique, 3rd ser. vol. xxxvi., 

 M. Laurent has published his views on the constitution of 

 several series of bodies which have been made the subjects of 

 investigation by other chemists. The first series subjected by 

 him to criticism comprises the bodies obtained by me from mad- 

 der, some of them being substances previously known and others 

 being new ; some contained as such in the plant, others products 

 of decomposition. The chief object of my investigation of mad- 

 der was to ascertain the nature of the chemical processes which 

 take place when madder is subjected to various agencies ; and 

 secondly, to discover the connexion, if any, subsisting between the 

 different substances of the plant which are endowed with colour, 

 and, if possible, to trace them back to some common origin, so as 

 to be able to exhibit them from a common point of view. The 

 direction in which the investigation ought to be conducted in order 

 to yield results of importance was first indicated by Berzelius, 

 who, while confessing his inability, notwithstanding the time he 

 had spent on experimenting to clear up this complicated subject, 

 expressed his conviction that the colouring matters of madder 

 possess great analogy of composition, and may perhaps be mu- 

 tually convertible. With what success my endeavours have been 

 attended I do not pretend to say ; but I do maintain, without 

 hesitation, that my view of the composition of the bodies examined 

 by me explains their formation and mutual relations more simply 

 and naturally than does M. Laurent's ; and I should have replied 

 much sooner to his objections had I not preferred waiting until 

 after the publication of the second part of my paper " On Rubian 

 and its Products of Decomposition *," in which a number of facts 

 are mentioned which will go further in confirming the views 

 maintained in the first part than any mere statement of opinions 

 could. 



I have described under the name of Rubian a substance con- 

 tained in madder of a very complex nature and high atomic weight, 

 which very readily undergoes decomposition. This substance 

 by its decomposition gives rise to the formation, not only of 

 alizarine, but of a number of other bodies, most of which possess, 

 either in a combined or uncombined state, a red colour. In fact, 

 all the bodies endowed with colour which have been obtained 



* Philosophical Transactions, part 1, 1853; Philosophical Magazine for 

 June 1853. 



