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



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 in- 

 creases in weight and bulk, in consequence probably of absorp- 

 tion of moisture from the air, and some chemical change is ef- 

 fected, which, though not attended by any striking phenomena, 

 is sufficiently well indicated by its results. There are few che- 

 mical 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 attempts to do so have merely consisted of ar- 

 guments based on analogy. It has been surmised tbat the pro- 

 cess is one of oxidation, and that the excess of atmospheric air 

 is consequently necessary. We are indeed acquainted with cases, 

 in which substances of well-defined character and perfectly colour- 

 less, as for instance orcine and hematoxyline, 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 oxidation is decomposed and gives 

 rise by its decomposition to the various substances endowed 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 mixtures, and some of them in the main 

 identical, has been satisfactorily proved by late investigators. But 

 there still remain a number, which, though extremely similar, 

 have properties sufficiently marked to entitle them to be con- 

 sidered as distinct. 



In my papers on the colouring matters of madder*, I have 

 described four substances derived from madder, only one of 

 which is a true colouring matter, but all of them capable, under 

 * Phil. Mag. August 1848, and September 1849. 



