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XVIII. On Rubicm and its Products of Decomposition. By Edward Schunck, F.R.S. 
Received January 9, — Read February 13, 1851. 
PART I. 
Among the many discussions to which the subject of madder has given rise among 
chemists, there is none which is calculated to excite so much interest as that concern- 
ing the state in which the colouring matter originally exists in this root, and there is 
no part of this extensive subject which is at the same time involved in such obscurity. 
It is a well-known fact that the madder root is not well adapted for the purposes of 
dyeing until it has attained a growth of from eighteen months to three years, and 
that after being gathered and dried it gradually improves for several years, after 
which it again deteriorates. During the time when left to itself, especially if in a 
state of powder, it increases in weight and bulk, in consequence probably of absorp- 
tion of moisture from the air, and some chemical change is effected, which, though 
not attended by any striking phenomena, is sufficiently well indicated by its results. 
There are few chemical investigations that have thrown any light on the nature of 
the process which takes place during this lapse of time, and in fact most of the at- 
tempts to do so have merely consisted of arguments based on analogy. It has been 
surmised that the process is one of oxidation, and that the access of atmospheric air 
is consequently necessary. We are indeed acquainted with cases, in which substances 
of well-defined character and perfectly colourless, as for instance orcine and hema- 
toxyline, are converted by the action of oxygen, or oxygen and alkalies combined, 
into true colouring matters. A more general supposition is, that the process is one 
of fermentation, attended perhaps by oxidation, and in confirmation of this view the 
formation of indigo-blue from a colourless plant, by a process which has all the cha- 
racters of one of fermentation, may be adduced. What the substance is however on 
which this process of oxidation or fermentation takes effect, what the products are 
which are formed by it, whether indeed the change is completed as soon as the 
madder has reached the point when it is best adapted for dyeing, or whether further 
changes take place when it is mixed with water and the temperature raised during 
the process of dyeing, are questions which have never been satisfactorily answered, if 
answered at all. It has indeed been suspected by several chemists, that there exists 
originally some substance in madder, which by the action of fermentation or oxida- 
tion is decomposed and gives rise by its decomposition to the various substances en- 
dowed either with a red or yellow colour, which have been discovered during the 
chemical investigations of this root. That several of these substances are merely 
