928 NEUTRAL COLOURING MATTERS. 



and dull, owing to the Madder brown being fixed in the cloth, 

 as well as the madder purple and madder red. The object of 

 (5) the clearing process is to get rid of the brown which is not 

 nearly so fixed as the red. It consists of boiling the cloth in 

 alkali and soap ; afterwards with soap and protochloride of tin 

 under a pressure of two atmospheres, and finally exposing the 

 cloth on the grass to the sun for a few days. 



If the cloth be prepared and dyed with madder in the same 

 manner, with the exception of charging it with an iron instead of 

 an aluminous mordant, it is dyed of a beautiful and permanent 

 purple, instead of red.* 



CARTHAMIN. 



Safflower consists of the flowers of Carthamus tinctorius; it 

 contains two colouring matters, a yellow, which is of no value, 

 and a beautiful but fugitive red used in silk dyeing, which is 

 named carthamin or carthamic acid. The yellow matter is 

 soluble in water, the red insoluble in water but soluble in alka- 

 lies. They ure separated by adding an acid to an alkaline in- 

 fusion of saiflower, which throws down the carthamin, and 

 afterwards passing clean cotton yarn through the liquid ; in 

 these circumstances, the yarn takes up the carthamin entirely 

 and is then washed with water. The pure carthamin is afterwards 

 stript from the cotton by an alkali and the solution is employed 

 to dye silk by acidulating with citric acid, and then passing the 

 silk through the liquid in the usual way by means of a winch. 



The pigment rouge contains precipitated carthamin intimately 

 mixed with finely divided talc. 



According to Doebereiner, carthamin has an acid reaction ; 

 it is but slightly soluble in alcohol or ether. Soda saturated 

 with carthamin is said to crystallize in fine colourless needles 

 having a silky lustre, and becoming instantly red when an acid 

 is added. 



HEMATOXYLIN. 

 I 



This is the colouring matter of logwood, the wood of the 

 H&matoxylon campeachianum ; it was named Hematin by 



* An outline of the process of Turkey red dyeing as practised at Glasgow is 

 given by Dr. Thomson, in his Organic Chemistry, Vegetables, p. 396. For this 

 and other dyeing processes, see also Leuch's Traite complct des Matieres Tmc- 

 vriales. 



