69 
It was stated in the last Lecture, that all the 
different parts of plants are capable of being de- 
composed into a few elements. Their uses as 
food, or for the purposes of the arts, depend upon 
compound arrangements of those elements which 
are capable of being produced either from their 
organized parts, or from the juices they contain ; 
and the examination of the nature of these sub- 
stances is an essential part of Agricultural 
Chemistry. 
Oils are expressed from the fruits of many plants : 
resinous fluids exude from the wood ; saccharine 
matters are afforded by the sap ; and dyeing 
materials are furnished by leaves, or the petals of 
flowers : but particular processes are necessary to 
separate the different compound vegetable sub- 
stances from each other, such as maceration, in- 
fusion or digestion in water, or in spirits of wine : 
but the application and the nature of these pro- 
cesses will be better understood when the chemical 
nature of the substances is known ; the consider- 
tion of them will therefore be reserved for another 
place in this Lecture. 
The compound substances found in vegetables 
are, 1. gum, or mucilage, and its different mo- 
difications ; 2. starch ; 3 . sugar ; 4. albumen ; 5. 
gluten ; 6. gum elastic ; 7* extract ; 8. tannin ; 9. 
indigo; 10. colouring principles; 11. bitter prin- 
ciples ; 12. wax ; 3. resins ; 14. camphor ; 15. 
fixed oils ; 16. volatile oils; 17 . woody fibre ; 18. 
acids ; 19. alkalies ; earths, metallic oxides, and 
saline compounds. 
1 shall describe generally the properties and 
f 3 
