Dr. Schunck on the Colouring Matters of Madder. 143 



gelatinous white precipitate, lime and baryta water thick gelatinous 

 pink precipitates, common salt a flocculent precipitate, nitrate of 

 potash a flocculent precipitate, sugar oflead a gelatinous reddish pre- 

 cipitate, sulphate of copper a gelatinous greenish precipitate, cor- 

 rosive sublimate no precipitate. On evaporating the watery solution, 

 the substance separates on the surface of the fluid in the shape of a 

 pellicle, and is left at last as a brownish extract, which may easily 

 be detached from the sides of the vessel. In solutions of caustic 

 and carbonated alkalies it first swells up, and on heating the fluid it 

 dissolves with a light red colour, forming slimy fluids, from which 

 it is precipitated by acids in flocks. Solutions of salts, even of 

 alkaline salts, produce precipitates in the alkaline solutions. It is 

 decomposed by boiling concentrated nitric acid. When heated on 

 platinum foil it burns without melting, leaving a considerable ash. 

 It seems that the pectic acid from madder retains in combination 

 with it a portion of colouring matter, from which it cannot be sepa- 

 rated. Hence the red colour with which it dissolves in alkalies. 



Concerning the two fats which I mentioned above as constituents 

 of the brown precipitate, I have little to say. They also retain in 

 combination a quantity of colouring matter, from which I have found 

 it impossible to separate them. They are both soluble in alcohol, 

 but one more so than the other. One of them dissolves with ru- 

 biacin in perchloride of iron, the other not. The former is more 

 easily fusible than the latter, but both melt below the temperature 

 of boiling water. 



I shall conclude this paper with some practical deductions which 

 I have made from the experiments detailed in the preceding. 



Few subjects connected with the arts have raised so much dis- 

 cussion as the nature of the process of madder-dyeing. The inves- 

 tigation of Robiquet on this subject, instead of clearing it up, seemed 

 only to add to its complexity. He considered his alizarin as the 

 substance mainly concerned in the production of madder colours. 

 This has been denied by others, though I think on insufficient 

 grounds. A remarkable discovery in regard to madder-dyeing, was 

 the fact that lime is very essential in this process. It was found that 

 madder, if not grown on calcareous soil, is incapable of producing 

 fast colours, but that if in this case chalk be added to the madder 

 during dyeing, or if calcareous water be employed, the desired effect 

 is produced. This again has given rise to endless discussions. It 

 was found by Persoz that the minutest quantity of lime added to 

 alizarin impaired its colouring power during dyeing, and the effect 

 of lime in madder-dyeing appeared to him an inexplicable mystery. 

 I will not enter further into the disputes on this subject, but shall 

 state at once my own views. It seems to me that former investiga- 

 tors have erred in supposing that madder contained only one colour- 

 ing matter, whereas I think I have proved that there are two, per- 

 fectly distinct and definite, alizarin and rubiacin, which perform 

 distinct functions during the process of dyeing. I have found, as 

 I stated above, that of the two colouring matters, alizarin and ru- 

 biacin, the former is the only one that is capable of dyeing when 



