4O4 COMPOUND PRODUCTS. CHAP. I. 



they denominate the colouring principle, and which 

 they have accordingly endeavoured to isolate and 

 extract ; first by means of maceration or boiling in 

 water, and then by precipitating it from its 

 solution. 



Properties. The chemical properties of colouring matter 

 seem to be, as yet, but imperfectly known, though 

 they have been considerably elucidated by the in- 

 vestigations of Bertholet, Chaptal, and others. Its 

 affinities to oxygene, alkalies, earths, metallic oxides, 

 and cloths fabricated whether of animal or vege- 

 table substances, such as wool or flax, seem to be 

 among its most striking characteristics. But its 

 affinity to animal substances is stronger than its 

 affinity to vegetable substances ; and hence wool 

 and silk assume a deeper dye, and retain it longer, 

 than cotton or linen. Colouring matter exhibits a 

 great variety of different tints as it occurs in dif- 

 ferent species of plants ; and as it combines with 

 oxygene, which it absorbs from the atmosphere, it 

 assumes a deeper shade. But it loses at the same 

 time a portion of its hydrogene, and becomes inso- 

 luble in water ; and thus it indicates its relation to 

 extract. 



Species. Such are the general properties of colouring 

 matter. But chemists have also instituted specific 

 differences. Bucquet instituted a distinction by 

 which colours were divided into the extractive or 

 soapy, the earthy, the resinous, and the oily ; and 

 Fpurcroy reduced them also to the four following 



