Chemical Manufactures. 113 



It affords very readily a brilliant red with alumina, and a black 

 or purple with iron ; and very little of it is sufficient to produce 

 shades of great intensity. Madder itself, if used for the same 

 purpose, would require a tedious and complicated process. 



Purpurine, or madder purple, the other red colouring" 

 matter, resembles alizarine, from which it may be separated by 

 a boiling solution of alum, and, after cooling, may be thrown 

 down by excess of sulphuric or muriatic acid. It produces, 

 with mordants, a more fiery red, and a more intense black, 

 than alizarine ; but the purple it gives has a very disagreeable 

 reddish hue, and hence its name has not been well chosen. Its 

 colours are not only inferior to those of alizarine, but less per- 

 manent. 



The precipitate thrown down by an acid from infusions of 

 madder, contains also rubiacine or madder oranae., a yellow 

 colouring matter which sublimes in yellow crystals. It may 

 be conveniently obtained by digesting washed madder roots 

 for sixteen hours in eight parts of water at 60°, and straining 

 the liquid, which will then deposit small crystals. When these, 

 after having been dried, are dissolved in boiling alcohol, crys- 

 tals will separate on cooling, and must be washed with cold 

 alcohol. Rubiacine, as also the two resinous colouring matters 

 contained in madder, injure the beauty of the dyes obtained 

 from it, giving to the red an orange, and to the purple a red 

 tinge, and a yellowish hue to those parts of the cloth which 

 should be white. 



It is a curious circumstance that madder, to produce per- 

 manent colours, must contain a certain amount of lime, either 

 naturally or from its having been added. Hence dilute sul- 

 phuric or muriatic acid, injures its dyeing powers, but they 

 may be restored. Something, therefore, depends on the soil 

 in which the madder is grown, or on the water used in dyeing 

 with it ; if these do not supply the required carbonate of lime, 

 the effect produced will be imperfect. Lime water neutralizes 

 the injurious effects of the pectic acid, rubiacine, and resinous 

 matters, in the madder ; but excess of it would combine with 

 the alizarine. If, in dyeing, only the latter is used, the smallest 

 quantity of lime would be mischievous, since it would prevent 

 .the combination of the dye with the mordants, which are 

 weaker bases. 



Many unsuccessful attempts having been made to improve 

 the colouring properties of madder, it was at length discovered 

 that by acting upon it with strong sulphuric acid, and then 

 washing with water, a more powerful and brilliant dye might 

 be obtained. It is believed that the acid decomposes the 

 bitter principle, producing new quantities of colouring matter ; 

 and that it liberates colouring matter which was in combination, 



