208 Dr. Schunck on Colouring Matters. 



and changed into a yellow flocculent substance. It was soluble in 

 concentrated sulphuric acid, forming a brown liquid, and was re- 

 precipitated by water. I consider this substance, that formed in a 

 solution of xanthine during evaporation by heat, and the dark brown 

 substance contained in the precipitate produced by acids in a decoc- 

 tion of madder as the same, and that they are all produced from 

 xanthine by the action of the oxygen of the air. 



It still remains for me to say a few words on the substances left 

 behind in the root, after madder has been exhausted with boiling 

 water. It has for some time been well known that if madder, which 

 has already been used for the purpose of dyeing, be treated with a 

 strong acid such as sulphuric or muriatic, and the acid be then 

 carefully removed by washing with cold water, it is capable of being 

 again used for dyeing in the same way as fresh madder. It is in this 

 manner that the article known in commerce as garanceux is manu- 

 factured. This is a convincing proof that it is impossible to extract 

 the whole of the colouring matter by means of boiling water, and 

 that part of it must remain behind in some state in which it is inso- 

 luble in water. A quantity of madder was treated with boiling 

 water until the liquor gave absolutely no more precipitate on the 

 addition of muriatic acid. A very long boiling was necessary for 

 this purpose. The colour of the madder was changed by this 

 process from yellowish-brown, as it appears in the fresh state, to 

 a dull red. It was then treated with boiling caustic potash ley. A 

 liquor of a brownish colour was obtained, in which muriatic acid 

 produced a gelatinous precipitate of a brown colour. This was se- 

 parated by liltration, and, after being washed with cold water in 

 order to remove all the muriatic acid, was treated with a large 

 quantity of boiling water, in which it proved to be almost entirely 

 soluble. The solution was light brown. It gave gelatinous preci- 

 pitates with acids, with lime and baryta water, alcohol and most 

 salts. On evaporation it left a substance in light brown, transpa- 

 rent, brittle scales, which turned out to be pectic acid, much purer 

 indeed than that obtained in the first instance from the aqueous de- 

 coction. No colouring matter, or any other substance besides pectic 

 acid, seemed to be extracted by the caustic alkali. 



Another quantity of madder which had been completely ex- 

 hausted by boiling water, was treated with boiling muriatic acid, and 

 the liquid, after the boiling had been kept up for some time, was 

 strained through a cloth and supersaturated with ammonia, which 

 produced a pinkish-white precipitate. This precipitate was thrown 

 on a filter and carefully washed. The liquid contained an abun- 

 dance of lime and magnesia, A part of the pinkish-white precipitate 

 was dried and heated to redness in a crucible. During ignition a 

 gas came off which was without odour, and burnt with a blue flame, 

 being probably carbonic oxide. After complete ignition it dissolved 

 in muriatic acid with an effervescence of carbonic acid, but without 

 leaving much carbonaceous residue. On adding ammonia to the 

 solution a white precipitate was again produced. The filtered liquid 



