>4 On Madder, and 



purple or madder-red, as the tin mordant forms with these, 

 reddish compounds. When boiled with soap, madder- 

 orange is deteriorated. It loses its lustre, and becomes dull 

 and reddish. Carbonate of soda (1 to 8 cloth) produces a 

 similar, though less intense colour. In both cases, the 

 solutions are coloured yellow. By boiling with clay, the 

 orange loses some of its yellow lustre and becomes lighter. 

 Light injures this colour. Exposure to a July sun for 60 

 hours, causes it to lose the half of its colour. A specimen 

 dyed with chalk is deteriorated still more rapidly. From 

 the preceding observations, it appears, that the best mor- 

 dants for madder-orange as a dye, are alumina and oxide 

 of copper. 



Madder-yellow . — The distinction of this dye chiefly de- 

 pends upon its great solubility in water, and its want of 

 disposition to combine with cotton dipped in a solution of 

 alum. The Dutch madder, is especially, rich in madder- 

 yellow. It may be separated by digesting 1 part of 

 Dutch-madder with 16 water, boiling the solution after 

 12 hours, and mixing it with an equal volume of lime 

 water. In 12 hours a dark red precipitate is formed, which 

 besides madder-yellow, contains the other constituents of 

 madder, especially, madder- orange and madder-purple. 

 To separate these, an excess of acetic acid is added to the 

 precipitate, which dissolves the lime and madder-yellow, 

 and leaves a red mass which is separated by filtration. The 

 madder-yellow mixed with the acetate of lime is still ren- 

 dered impure by the presence of some madder-purple. 

 This is separated by boiling the solution with cotton im- 

 pregnated with alum mordant, as long as it is coloured red 

 or orange. A point is at last attained, where the cotton 

 acquires a bright rust colour, and the yellow liquid on eva- 

 poration , leaves not a brown-red, but a bright yellow residue; 

 the colouring matters are then completely separated. The 

 yellow residue is now dissolved in spirit, and the madder- 

 yellow precipitated from its solution, by means of an alco- 

 holic solution of acetate of lead. A scarlet-red precipitate 

 falls, which is to be edulcorated with spirit, then dissolved 

 in water, and precipitated by sulphuretted hydrogen, by 

 which means the madder-yellow is separated from the oxide 

 of lead. Since, cotton impregnated with alum mordant 

 acquires only a dull nankin colour, by the addition of 



