1835.] Madder Dyeing. 466 



It imparts to the cotton which has received the mordant a 

 dark-red colour, when in excess ; but when the cotton is in 

 excess a brick-red colour is produced. Boiling solution of 

 alum does not dissolve the madder-red. When this happens 

 it proceeds from madder-purple or madder-orange being 

 mixed with it. Caustic potash forms a fine violet-purple 

 solution. Solution of carbonate of soda forms a red liquid 

 which becomes blue by the addition of potash. Sulphuric 

 acid forms a brick-red solution. 



3. Madder-orange^ a yellow crystalline powder. It im- 

 parts to the mordanted cotton a bright orange colour when 

 in excess, but paler when the cotton is in excess. Boiling 

 solution of alum forms with the madder-orange an orange- 

 yellow solution, which, on cooling, deposits a little colour- 

 ing matter. Caustic potash produces a dark rose-colour. 

 Solution of carbonate of soda affords an orange-coloured 

 liquid. Sulphuric acid produces an orange-yellow colour. 



4. Madder-yellota, a yellow gummy mass ; communicates 

 to the mordanted cotton a pale nankin colour, and is not a 

 true dye. 



5. Madder-brown, a brownish-black dry mass ; communi- 

 cates no colour to cotton ; neither is it soluble in water nor 

 in spirit-of-wine. 



6. Madderic acid (Krapfsaure) is a colourless acid. 



7. Ruhiacic acid is also a colourless acid ; by heating with 

 muriatic acid, it is converted into a matter which forms a 

 clear blue colour, but cannot be fixed upon cotton. 



The three first of these alone deserve an attentive con- 

 sideration, in so far as manufacturers are concerned. 

 i Madder purple. — The separation of madder purple in a 

 state of purity is attended with considerable difficulty. It 

 is effected by the following operations : 1 . Washing the 

 madder with water of the temperature bQ^^ to 70° F. 2. 

 Boiling the washed madder with a strong solution of alum. 

 3. Precipitating the madder purple from the alum solution 

 by means of sulphuric acid. 4. Edulcorating and boiling 

 the precipitated madder purple with water, and then with 

 dilute muriatic acid. 5. Taking up the boiled madder 

 purple with spirit of wine of 90°. 6. Evaporating the spirit 

 of wine solution to the point of crystallization. 7. Dissolv- 

 ing again the crystallized madder purple in hot spirit of 

 wine, and re-crystallizing. The madder purple obtained 



