SIR H. DAVY S AGRICULTURAL CHEMISTRY. 



163 



and kneaded in the hands, or rubhed in a 

 mortar for some time, under cold water; 

 if it contain much gluten, tliat principle 

 Avill separate in a coherent mass. After 

 this process, whether it has afiorded glu- 

 ten or not, it should be kept in contact 

 with half a pint of cold water for three or 

 four hours, being occasionally rubbed or 

 agitated: the solid matter should be sepa- 

 rated from the fluid by means of blotting 

 paper; the fluid should be gradually heat- 

 ed; if any flakes appear, they are to be 

 separated by the same means as the solid 

 matter in the last process, i. e. by filtra- 

 tion. The fluid is then to be evaporated 

 to dryness. The matter obtained is to be 

 examined by applying moist paper, ting- 

 ed with red cabbage juice, or violet juice, 

 to it: if the paper become red, it contains 

 acid matter; if it become green, alkaline 

 matter; and the nature of the acid or al- 

 kaline matter may be known by applying 

 the tests described, pages 149, 150, and 

 151. If the solid matter be sweet to the 

 taste, it must be supposed to contain su- 

 gar; if bitterish, bitter principle or ex- 

 tract; if astringent, tannin; and if it be 

 nearly insipid, it must be principally gum 

 or mucilage. To separate gum or muci- 

 lage from the other principles, alcohol 

 must be boiled upon the solid matter, 

 which will dissolve the sugar and the ex- 

 tract, and leave tlie mucilage; the weight 

 of which may be ascertained. 



To separate sugar and extract, the al- 

 cohol must be evaporated till crystals 

 begin to fall down, which are sugar; hut 

 they will generally be colored by some 

 extract, and can only be purified by re- 

 peated solutions in alcohol. Extract may 

 be separated from sugar by dissolving the 

 solid, obtained by evaporation from alco- 

 hol, in a small quantity of water, and 

 boiling it for a long while in contact with 

 the air. The extract will gradually I'all 

 down in the form of an insoluble powder, 

 and the sugar will remain in solution. 



If tannin exist in the first solution 

 made by cold water, its separation is 

 easily effected by the process described 

 pages 124 and 125. The solution of 

 isinglass must be gradually added, to pre- 

 vent the existence of an excess of animal 

 jelly in the solution, which might be mis- 

 taken for mucilage. 



When the vegetable substance, the sub- 

 ject of experiment, will afford no more 

 l^rinciples to cold water, it must be ex- 

 posed to boiling water. This will unite 

 to starch if there be any, and may like- 

 wise take up more sugar, extract, and 

 tannin, provided they be intimately com- 

 bined with the other principles of the 

 compound. 



The mode of separating starch is. simi- 

 lar to that of separating mucilage. 



If after the action of hot water anything 

 remain, the action of boiling alcohol is 

 then to be tried. This will dissolve re- 

 sinous 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 application is scarcely ever necessa- 

 ry; for if this principle be present, it may 

 be easily detected by its peculiar quali- 

 ties. 



If any fixed oil oi* wax exist in the ve- 

 getable substance, it will separate during 

 the process of boiling in water, and may 

 be collected. 



Any substance not acted upon by wa- 

 ter, alcohol, or ether, must be regarded as. 

 woody fibre. 



If volatile oils exist in any vegetable 

 substances, it is evident they may be pro- 

 cured, and their quantity ascertained, by 

 distillation. 



When the quantity of fixed saline, al- 

 kaline, metallic, or earthy matter in any 

 vegetable compound, 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, bypass- 

 ing it through an ignited porcelain tube. 

 The nature of the matter so ])roduced, 

 may be learnt by applying the tests men- 

 tioned in pages 151 and 152. The only 

 analyses in which the agricultural che-. 

 mist can often wish to occupy himself, 

 are those of substances containing princi- 

 pally starch, gluten, sugar, oils, mucilage, 

 albumen, and tannin. 



The two following statements will af- 

 ford an idea of the manner in which the 

 results of experiments may be arranged. 



The first is a statement of the compo- 

 sition of ripe peas, deduced from experi- 

 ments, made by Einhof; the second are 



