56 REPORT — 1873. 



of Runge by processes very similar to those employed by Runge, and analyzed 

 these substauces : for madder-red he gives the formula C^g Hi^ Og, which differs 

 only by H^O from the formula now adopted ; for the madder-purple he gives the 

 formula C^^HjoOu, and for the same substance after being sublimed CjHgO^. The 

 chemist who has worked most on this subject, and to whom we are principally 

 indebted for what we know with regard to the different constituents contained in 

 the madder-root, is Dr. Schunck, of Manchester. In Liebig's 'Annalen' for 1848 

 he gives a long and interesting account of his examination of madder; he isolates 

 and identifies several new substances, which are most important constituents of the 

 root, and has since that time added much to our knowledge of the chemical constitu- 

 tion of madder. In the paper above alluded to he confirms the presence of the alizarin, 

 and gives to it the formula CnHj^O^. The principal properties of this body may 

 best be sketched in here. Its volatility and brilliant crystalline appearance have 

 already been mentioned ; it is but slightly soluble in cold water, but much more so 

 in alcohol, in ether, and in boiling water. The colour of its solution is yellow ; 

 and when it separates out from a liquid it has a yellow flocculent appearance, 

 differing thus greatly from the red, brilliant, crystalline substance before described. 

 In order to obtain this latter body, heat had always been used ; so, until the ela- 

 borate experiments of Schunck, it was a question whether the heat did not produce 

 a radical change in the substance, whether, in a word, these two bodies were 

 really identical. Schunck's experiments proved that they were, and consequently 

 that this beautiful colouring-matfer, alizarni, existed as such in madder. If, how- 

 ever, we go one step further back and examine the fresh root of the Subia tinc- 

 torum (that is, as soon as it is dravra from the ground), we shall find no trace of alizarin 

 there. On slicing the root it is seen to be of a light carroty colour, and an almost 

 colourless liquid can be squeezed out of it; but this is entirely free from the 

 colouring-matters of madder. Let the roots, however, be kept, if only for a short 

 time, and then they will give abundant evidence of the presence of alizarin ; if 

 simply heated, alizarin may be volatilized from them. It appears, then, that the 

 whole of the tinctorial power of this root is developed after the death of the 

 plant. Schunck explains this curious phenomenon as follows: — In the cells of 

 the living plant there is a substance which he has isolated and has named 

 Rubian ; it is easily soluble in water and in alcohol : the solution is of a yellow 

 colour, and has an intensely bitter taste ; when dry it is a hard brown gum-like 

 body. It has none of the properties of a dye-stuff'; but if we take a solution of it, 

 add some sulphuric or hydrochloric acid to it, and boil, a yellow flocculent sub- 

 stance will slowly separate out, and on filtering it off" and washing it, it will be 

 found to have the tinctorial properties of madder, and to contain alizarin. In the 

 liquid filtered from it there is, with the acid added, an uncrystallizable sugar ; so 

 that in this way the original product in the root, the rubian, has apparently been 

 split up into alizarin and into sugar. To apply this reaction to what goes on in 

 the root after its removal from the ground, we have to find if any other substances 

 can take the place of the boiling dilute acid ; and Schunck has shown there exists in 

 the root itself a substance which is eminently fitted to produce this splitting-up of 

 the rubian. He obtained this decomposing agent from madder simply by digest- 

 ing it in cold water and adding alcohol to the liquid ; this threw down a reddish 

 flocculent substance ; and if only a small portion of this was added to an aqueous 

 solution of the rubian and allowed to stand for a few hoiu-s in a warm place, it 

 was found that the rubian was gone, and in place of it there was a thick tenacious 

 jelly ; this, treated with cold water, gave to it no colour, no bitter taste, but much 

 sugar. From the jelly remaining insoluble, alizarin could be extracted; in fact, 

 of all known substances this very one found in the madder itself is best suited for 

 eflecting this decomposition of the rubian. 



It has long been known to dyers that the amount of colouring-matter in madder 

 will increase on keeping it ; even for years it will go on improving in quality : and 

 an experiment of Schunck's shows that the ordinary madder, as used by the dyer, 

 has not all the rubian converted into colouring-matter ; for on taking a sample of 

 it and extracting with cold water, he got an acid solution devoid of dyeing proper- 

 ties; but on allowing this solution to stand some time it gelatinizetl, and then 

 possessed dyeing properties. 



