To separate sufrar and extract, the alcohol nnust 

 be evaporated till crystals bejrin to fall down, 

 which are sugar; but they will generally be co- 

 loured by some extract, and can only be purified 

 by repeated solutions in alcohol. Extract may be 

 separated from sugar by dissolving the solid, ob- 

 tained by evaporation from alcohol, in a small 

 quantity of water, and boiling it lor a long while 

 in contact with the air. The extract will gradu- 

 ally fall down in the form of an insoluble powder, 

 and the sugar will rem.iin in solution. 



If tannin exist in the first solution made by 

 cold water, its separation is easily effected by the 

 process belbre described. The solution of isin- 

 glass must be gradually added, !o prevent the ex- 

 istence of an excess of animal jelly in the solution, 

 which might be mistaken for mucilage. 



When the vegetable substance, the subject of 

 experiment, will aflbrd no more principles to cold 

 water, it must be exposed to boiling water. This 

 will unite to starch, if there be any, and may 

 likewise take up more sugar, extract, and tannin, 

 provided they be intimately combined with the 

 other principles of the compound. 



The mode of separating starch is similar to that 

 of separating mucilage. 



If after the action of hot water any thing re- 

 main, the action of boiling alcohol is then to be 

 tried. This will dissolve resinous matter; the 

 quantity of which may be known by evaporating 

 the alcohol. 



The last agent that may be applied is ether, 

 which dissolves elastic gum, though the applica- 



tion is scarcely ever necessary; for if this principle- 

 be present, it may be easily detected by hs pecu- 

 liar qualities. 



If any fixed oil or wax exist in the vegetable' 

 substance, it will separate during the process of 

 boiling in water, and may be collected. Any sub- 

 stance not acted upon by water, alcohol, or "ether, 

 must be refrarded as woody fibre. 



If volatile oils exist in any vegetable substances, 

 it is evident they may be procured, and their quan- 

 tity ascertained, by distillation. 



When the quantity of fixed saline, alkaline, 

 metallic, or earthy matter in any vegetable com- 

 pound is to be ascertained, the compound must be 

 decomposed by heat, by exposing it, if a fixed 

 substance, in a crucible, to a long continued red 

 heat; and if a volatile substance, by passing it 

 through an ignited porcelain tube. The nature of 

 the matter so produced may be learned by applying 

 the tests mentioned in Lecture TV. 



The only analyses in which the agricultural 

 chemist can often wish to occupy himself, are 

 those of substances containing principally starch, 

 sugar, gluten, oils, mucilage, albumen, and tan- 

 nin. 



The two following statements will afford an idea 

 of the manner in which the results of experiments 

 innv be arranged. 



The first is a statement of the composition of 

 ripe peas, deduced fi-om experiments made by 

 Einliof; the second is of the products afforded by- 

 oak bark, deduced from experiments conducted by 

 myself. 



