SECT. VIII. COLOURING MATTER. 403 



finally deposited by evaporation the peculiar ex- 

 tractive. It is insoluble in cold water; but very 

 soluble in boiling water ; its colour is brown, and 

 its taste bitter. It is precipitated from its solution, 

 by lime water, in the form of a red powder ; and 

 when dry it is black and brittle, breaking with a 

 polished fracture. 



Extract of Saffron. This extract is obtained 

 in great abundance from the summits of the pistils 

 of Crocus sativus, which are almost wholly soluble 

 in water. 



Extracts were formerly much employed in me- Use$, 

 dicine ; though their efficacy seems to have been 

 over-rated. But a circumstance of much more im- 

 portance to society is that of their utility in the 

 art of dyeing. By far the greater part of colours 

 used in dyeing are obtained from vegetable extracts, 

 which have a strong affinity for the fibres of cotton 

 or linen, with which they enter into a combination 

 that is rendered still stronger by the intervention 

 of mordants. 



SECTION VIII. 

 Colouring Matter. 



THE beauty and variety of the colouring of ve- A peculiar 

 getables has always been the subject of the admi- su 

 ration of mankind. What is the cause of that 

 beauty and variety ? Chemists have ascribed it to 

 the modifications of a peculiar substance which 



2 D 3 



