285 



small quantities of resinous and other substances, which are 

 insoluble by themselves in pui'e water. 



The reagents used for testing the aqueous solutions of any 

 vegetable matter and brought into the order in which they might 

 be employed most conveniently, are as follows : — 



Blue litTiius-jyaper. — A red colouration of it indicates free acids 

 or acid salts. Extracts of vegetables will always produce this 

 effect. 



Yellow titr77ieric-pape}: — A brown colouration of it would indi- 

 cate basic salts, but such an effect has scarcely ever been obtained 

 with vegetable extracts. 



Bed lit'mus-2)a2)er may be dispensed with in most cases, yet it 

 happens sometimes that an alkaline reaction is recognised more 

 easily with this paj^er than with turmeric-paper. 



All other tinged papers, as those of dahlia, violets, &c., are 

 inferior to the above three. 



jEthey (of 0'720 specific gravity) frequently produces turbidity 

 even in small quantity, but it is best to add as much as the watery 

 liquid is able to dissolve, or until a small quantity of ether floats 

 on the aqueous sohation after the mixture has been well agitated 

 for some time. The turbidity may be produced by gum, by salts of 

 anorganic bases with anorganic or organic acids, by 2:)rotein sub- 

 stances, humus-like matters, &c. 



Alcohol (of 0'815 specific gravity) usually efiects no alteration 

 when added in small quantity; therefore more of it is requii-ed 

 than of ether, or on the average a quantity equal in bulk to the 

 aqueous liquid. A turbidity, obtained hereby, is mostly caused 

 by gum. 



Liquor of ammonia (of 0'960 specific gravity) imparts clearness 

 ■to liquids which possess an opalescent a])pearance {see above) from 

 traces of resins. Coloured liquids become darker with it. But 

 ammonia may also produce precipitates; should any of them dis- 

 appear on the addition of alcohol, it is with tolerable certainty 

 to be concluded that an alkaloid is present. The same conclusion 

 is justified when a further addition of ammonia acts redissolvingly 

 on the precipitate, and therefore the precaution should be used to 

 apply the reagents only successively drop by drop, because sudden 

 large additions would redissolve any otherwise visible precipitate, 

 and prevent its being noticed. 



Should the precipitate, obtained with ammonia, disappear 

 neither with alcohol nor with an excess of ammonia, it may be 

 either alumina or phosphate of lime, or phosphate of ammonia- 

 magnesia or oxalate of lime. The first of these precipitates is 

 flocky and soluble in potash-ley, also in acetic acid when newly 

 precipitated ; the second one is also flocky, and when newly pre- 

 cipitated, soluble in acetic acid, but not in potash-ley; the third 

 behaves towards acetic acid and potash-ley like the second, but is 



