448 The Art of Dyeing . 



a solution of iron alum (1 iron alum to GO water), pressed 

 and then washed. When it is dyed twice, it is mordanted 

 in the same solution, and afterwards buried for half an 

 hour in a solution of Avignon madder. The first colour, 

 which is darker than the second, is produced by means of 

 12 lbs. cloth, and 8 lbs. Avignon madder; the second by 

 12 lbs. cloth, and 14 lbs. Avignon madder. 



Properties of madder violet. — When passed through hot 

 soap-suds, the colour becomes blueish. When boiled for 

 ten minutes in the same mixture, it becomes, on the con- 

 trary, reddish and paler, without losing any of its clear- 

 ness. 



Solution of potash forms a violet spot, which is removed 

 by rinsing in water. 



Lime water, ammonia, and vinegar, have no action. 



Lime juice forms yellow spots, which are removed by 

 ammonia. 



Both of the tin mordants discharge a chamois colour. 



Solution of chloride of lime produces reddish white spots. 



Remark. The iron alum facilitates the exhibition of such 

 grounds, as are here noticed, in reference to its equable 

 distribution over the c-lico. Other salts of iron, as sul- 

 phate of iron, might be employed, but we are not so sure 

 that the cloth will be dyed free from spots. 



ALUM MORDANTS. 



Alum is employed as the mordants mentioned, for light 

 colourless grounds. We dissolve 5 lbs. alum in 300 water, 

 and impregnate the calico with it in the manner described, 

 by dipping, pressing, aiid rinsing. There remains in this 

 case, a considerable quantity of alum in combination with 

 the fibre of the calico. Hence, the colour, though pale., is 

 very equal. Oak bark, with alum, forms a pale yellow 

 colour; catechu with alum, a brown orange. 



Experiment shews that the same result follows, whether 

 we employ strong or weak solutions of alum, as mordants. 

 Calico only takes up a certain quantity of alum ; so that a 

 solution of alum, containing five times as much salt as that 

 given above, does not produce darker colours. If carbonate 

 of soda is added to the solution of alum, a mordant is ob- 



