Mr. J. Higgin on the Colouring Matters of Madder. 291 



alizarine had been merely thrown into an inactive condition 

 by the boiling water, the converting of the residue into ga- 

 rancine would certainly have restored its activity, and the 

 dyeing made with that garancine would have been superior to V***-%v+, 

 the other; but, on the contrary, the second results were not ■ V-^/// 

 even equal, the same remarkable difference occurring as in 

 the first instance. This shows that in the one case the tinc- 

 torial power was dependent on the alizarine existing normally 

 in the madder ; in the other, that the xanthine had contributed 

 a further portion. 



No. 5. Two equal portions of madder were again taken : 

 to one a certain quantity of water at 120° F. was added, and 

 the heat continued for half an hour ; a certain quantity of 

 dilute sulphuric acid then added, the mixture filtered, and the 

 mass washed with a known quantity of dilute sulphuric acid, 

 and afterwards with a known quantity of water. 



The other portion was mixed with the same quantity of 

 water and dilute acid as the former, filtered, and washed with 

 the same quantity of dilute acid and water. The two portions 

 thus treated were used to dye equal quantities of mordanted 

 cloth, with the usual precautions. The one which was sub- 

 jected to spontaneous action previous to washing with acid, 

 dyed full and rich shades ; that from which the xanthine had 

 been washed out unchanged, dyed shades very many times 

 weaker. 



In this experiment the two madders were under exactly 

 equal circumstances, except that one of them was allowed to 

 ferment the xanthine; yet the difference in result was very great, 

 and could only arise from the xanthine becoming available co- 

 louring matter. I consider these five experiments as clearly 

 demonstrating the value of xanthine in madder-dyeing. 



The madder used in this case was " ombro," a variety very 

 rich in xanthine, and therefore the best to test its value. 



With this theory of madder, the operation of dyeing be- 

 comes much more intelligible. It is known that, to dye well 

 with madder, the process must be begun at a low temperature 

 and the heat gradually raised. The application of the theory 

 will be this. The xanthine, on immersing the madder in 

 water, immediately begins to decompose, becoming rubiacine; 

 this in its turn becomes alizarine, and then the combination 

 between it and the mordanted cloth takes place. The dyeing 

 is begun by the alizarine already existing in the madder, and 

 continued by the quantity continually formed. The slow 

 heating of the liquor is very favourable to the change taking 

 place. Generally the temperature is about 130° at the end V»wm 

 of the first hour ; long before that, however, the xanthine has 



