THE VOLATILE PART OF PLANTS. 87 
chemical language, chloride of sodium—is formed when 
soda is mixed with chlorhydric acid, water being, in this 
case, produced at the same time. 
Test for acids and alkalies.—Many vegetable colors are altered by solu- 
ble acids or soluble bases, (alkalies, ) in such 2 manner as to answer the 
purpose of distinguishing these two classes of bodies. A solution of 
eochineal may be employed. It has aruby-red color when concentrat- 
ed, but on mixing with much pure water, becomes orange or yellowish- 
orange. Acids do not affect this color, while alkalies turn it to an intense 
carmine or violet-carmine, which is restored to orange by acids. 
Exp. 38.—Prepare tincture* of cochineal by pulverizing 3 grams of 
cochineal, and shaking frequently with a mixture of 50 c. ¢c. of strong 
alcohol and 200c. c. of water. After a day or two, pour off the clear 
liquid for use. 
To a cup of water add a few drops of strong sulphuric acid, and to an- 
other similar quantity add as many drops of ammonia. To the liquids 
add separately 5 drops of cochineal tincture, observing the coloration in 
each case. D vide the dilute ammonia into two portions, and pour into 
one of them tke dilute acid, until the carmine color just passes into 
orange. Should excess of acid have been incautiously used, add ammo- 
nia, until the carmine reappears, and destroy it again by new portions 
of acid, added dropwise. The acid and base thus neutralize each other, and 
the solution contains sulphate of ammonia, but no free acid or base. It 
will be found that the orange-cochineal indicates very minute quantities 
of ammonia, and tbe carmine-cochineal correspondingly small quantities 
ofacid. Tincture of litmus, (procurable of the apothecary,) or of dried 
ced cabbage, may also be employed. Litmus is made red by soluble 
ucids,and blue bysoluble bases. With red cabbage, acids develope a 
purple, and the bases a green color. 
In the formation of salts, the acids and bases more or less neutralize 
zach other's properties, and their compounds, when soluble, have a less 
sour or less acrid taste, and act less vigorously on vegetable colors than 
the acids or bases themselves. Some soluble salts have no taste at all 
resembling either their base or acid, and have no effect on vegetable col- 
ors. This is true of common salt, glauber salts or sulphate of soda, and 
saltpeter or nitrate of potash. Others exhibit the properties of their 
base, though in a reduced degree. Carbonate of ammonia, for example, 
has much of the odor, taste, and effect on vegetable colors that belong 
to ammonia, Carbonate of soda has the taste and other properties of 
caustic soda in a greatly mitigated form. On the other hand, sulphates of 
alumina, iron, and copper, have slightly acid caaracters. 
Certain acids form with the same base several distinct salts. Thus 
carbonic acid and soda may produce carbonate of soda, Na,zO CQs, or 
* Tinctures, in the language of the apothecary, are alcoholic solutions. 
