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 acid.i and alkalies. — Many vegetable colors are altered by solu- 

 ble acids or soluble bases, (alkalies,) in sucli a manner as to answer tlie 

 purpose of distiuguisliing these two classes of bodies. A solution of 

 cochineal may be employed. It has a ruby-red color when concentrat- 

 ed, but on mixing with much pure water, becomes orange or yellowish- 

 orange. Acids do not affect this color, while allcalies turn it to an intense 

 carmine or violet-carmine, which is restored to orauge by acids. 



Exp. 38. ■ — Prepare tincture* of cochineal by pulverizing 3 grams of 

 cochineal, and shalcing frequently with a mixture of 50 c. c. of strong 

 alcohol and 200 c. 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. Divide the dilute ammonia into two portions, and pour into 

 one of them tlie 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 tieutralise 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 the carmine-cochineal correspondingly small quantities 

 of acid. Tincture of litmus, (procurable of the apothecary,) or of dried 

 red cabbage, may also be employed. Litmus is made red by soluble 

 acids, and blue by soluble 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 

 each otfier'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 otiier properties of 

 caustic soda in a greatly mitigated form. On the other hand, sulphates of 

 alumina, iron, and copper, have slightly acid characters. 



Certain acids form with the same base several distinct salts. Thus 

 carbonic acid and soda may produce carbonate of soda, NajO CO2, or 



* Tinctures, in the language of the apothecaiy, are alcohoUo solutions. 

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