450 The Art of Dyeing. 



For the exhibition of the different dark colours, the dyer 

 should keep the three following mordants, or at least a suf- 

 ficient quantity of number 1, in order to mix the others. 

 Alum mordant, No. 1, 300 lbs. alum, 800 lbs. water, 300 

 lbs. sugar of lead. — Alum mordant, No. 2, 300 lbs. alum, 

 1200 lbs. water, 300 lbs. sugar of lead. — Alum mordant, 

 No. 3, 300 lbs. alum, 1600 lbs. water, 300 lbs. sugar of 

 lead . 



The preparation of these mordants requires the following 

 precautions : The alum should be bruised, and placed in 

 a wooden cask ; then hot water should be digested on it, 

 and the mixture stirred till the alum is dissolved. Then 

 the sugar of lead maybe added, the mixture stirred, and 

 allowed to become clear. These mordants are not fit for 

 use till after 24 hours. 



As the pounding of the alum is somewhat troublesome, 

 it may be dissolved in one half of the water at the boiling 

 temperature. The copper vessel in which this is performed 

 should, however, be protected by tin from the soluble power 

 of the alum. 



It is peculiarly advantageous, when employing madder 

 red, to add carbonate of soda to the mordant. 



For 300 lbs. alum we take 30 lbs. crystallized carbonate 

 of soda, dissolved in water. Add the alum solution gra- 

 dually to it, and then the sugar of lead. It would be an 

 error to add the soda after the sugar of lead ; in this case, 

 alumina would be precipitated, which would not again dis- 

 solve. 



All these mordants contain, by consequence, iron, when 

 the alum contained iron. To make a mordant free from 

 iron, the addition of prussiate of potash may be had re- 

 course to in the proportion of 1 lb. prussiate of potash to 

 300 lbs. alum. 



The prussiate of potash should first be dissolved in water, 

 and the boiling solution of alum added; the mixture being 

 stirred, a dark blue colour will be produced, which disap- 

 pears on the addition of the sugar of lead ; the sulphate 

 of lead taking up the Prussian blue, and falling to the bot- 

 tom. It is, however, necessary to mix the solution of the 

 prussiate of potash with the boiling solution of alum, and 

 to allow them to remain for some time in contact, or allow 



