Vegetable Substances. 281. 



sorbed, and carbonic acid gas emitted; whence 

 it is probable that starch is converted jnto sugar 

 by diminishing its proportion of carbon, and in- 

 creasing that of its hydrogen and oxygen. Its 

 distillation shows us that it contains no other 

 ingredient than these three *." 



10. Indigo is a matter obtained by fermenta- 

 tion from the plant which bears that name; it 

 may also be obtained from a plant well known 

 in this country by the name of ixoad. It has 

 been ascertained by experiment that indigo owes 

 its blue colour to oxygen; and its constituent 

 parts are oxygen, carbon, hydrogen, and nitro- 

 gen ; the two first are in a large proportion. 



11. Extractive principle is found in many 

 plants, but very different in kind. Saffron yields 

 it in great abundance. It has a near affinity, 

 and perhaps connexion, with the colouring 

 matter. 



12. Albumen^ by which term chemists denote 

 the white of an egg, or something analogous to 

 it, is found in several plants, particularly in the 

 juice of the papaw-tree of Peru. 



13. Gluten is an essential part of all farina- 

 ceous vegetables. It may be obtained from 

 wheat flour in abundance, by kneading it under 

 a small jet of water till the fluid carries off all 

 the starch, and runs off colourless. It has some 



* Dr. Thornton, 



