162 



ANIMAL COLOURING MATTERS. 



spins a thread of the most dazzling whiteness. But the colour 

 of raw silk from India, Italy, and France is yellow. Some ex- 

 periments on this colouring matter were made by Hoard in 1807.* 

 According to him it is a resinous substance, almost solid at the 

 temperature of 59, but quite fluid at 86. Its colour is red- 

 dish-brown while in lumps, but a fine greenish-yellow when in a 

 state of division. Silk contains from ^V^h to ^ 5 th part of it. Its 

 smell is strong, proceeding from a volatile oil which it contains. 

 Light bleaches it completely in a few days, when concentrated 

 solutions of it are exposed to its action. It is insoluble in water, 

 but very soluble in alcohol. The fixed alkaline leys, especially 

 ammonia, dissolve a little of it while cold, and the action is not 

 much increased by heat ; while soap, which has little action while 

 cold, is rather a powerful solvent of it at the temperature of boil- 

 ing water. Concentrated sulphuric and muriatic acids char it 

 immediately. Sulphurous acid partially bleaches it Chlorine 

 bleaches it instantly, converting it into a solid matter like wax. 



According to Mulder f the colouring matter of yellow silk has 

 a fine red colour. He obtained it in the following manner : 

 The alcoholic tincture of raw yellow silk is concentrated by dis- 

 tillation to a small quantity ; flocks of cerin are deposited. The 

 residual liquid being now evaporated, the colouring matter re- 

 mains mixed with fat and resin. From these substances it is 

 freed by digestion in a solution of caustic potash. This solution 

 must not be too strong, otherwise the fine red of the colouring 

 matter is rendered dark. 



This colouring matter is insoluble in water ; but very soluble 

 in alcohol, ether, fat and volatile oils. When placed in contact 

 with chlorine or sulphurous acid, it becomes light yellow ; indeed, 

 almost white. 



The quantity of colouring matter in raw yellow silk is, accord- 

 ing to Mulder, about ^ggth part of the silk. 



Ann, de Chimie, Ixv. 61. t Poggendorf's Annalen, xxxvii. 610. 



