This acid retains its oxygen with but little force, and hence it is decomposed by all combustible bodies, which deprive it of its oxygen with more or less rapidity.
PoUr strong nitric acid on some warm, dry, and finely powdered charcoal. The charcoal will become ignited, giving out an immense quantity of fumes.
Obi. The charcoal absorbs the oxygen from the acid, with such rapidity as to produce ignition.
.Exp. 3. Put half an ounce, or an ounce of oil of turpentine into a small cup ; then pour on it suddenly about half an ounce of strong nitric acid. The turpentine will burst into flame, with au explosion, sending forth an immense volume of black smoke.
Remark. In making tins experiment, the vessel containing the acid must be tied to a stick, so that the operator may stand at a yard or two distance, from the explosion.
Obs. The acid inflames the oil on the same principle that it ignites charcoal.
357. Nitric acid dissolves silver, copper, zinc, &c. The solution is more rapid if the acid is diluted with water.
Obs. This acid is called aqua fortis, and under this name is of important use in the arts.
358. When nitric acid is submitted to the action of copper, and some other metals, a part of its oxygen is imparted to the metal, and of consequence the nitric is converted into the nitrous acid.
359- This acid combines with the alkalies, earth, and metallic oxides, and forms a class of compounds called nitrates. Most of these 3alts deflagrate when thrown on red hot charcoal.
360. Nitrous acid. When nitrate of potash is exposed to a degree of heat sufficient to deprive it of a part of its oxygen, and the process is then stopped, and the salt submitted to the action of sulphuric acid and heat, there comes over what is called nitrous acid.
Obs. When nitric acid is charged with the red fumes of nitrous gas, as in the beginning of the process for obtaining this acid, it is more commonly called nitrous acid. Indeed, chemists have doubted whether there existed an acid properly denominated nitrous, and which bore the same relation to the nitric, that sulphurous acid does to sulphuric. By the above process, an acid is obtained which contains less oxTgen than the colourless nitric acid. But this same acid win become colourless by exposure to the air, the red fumes readily making their escape; and it is well known, that whatis called nitric acid contains various proportions of oxvgen. Now whether what is denominated nitrous acid, is a definite, and distinct compound, or whether it is nitric acid containing a quantity of nitrous gas, which gives it colour, is a question on which chemists are divided. Mere dilution with water will change the colour of this acid. Thus the orange colour will pass through the shades of blue, olive, and bright green, by adding successive portions of water.
Some good authorities, however, maintain that the nitrous acid is a distinct compound, but it is difficult to point out to the student, any distinctions by which the difference between the two acids may be obvious, except that the nitrous acid contains the red fumes of nitrous gas, while the nitric acid is without colour; still the coloured acid may be much stronger than the colourless.
It does not seem that the combinations of this acid with the different bases, afford compounds which differ from the nitrate, there being, it is believed, no compound which bean the name of nitrite.
361. Carbonic Acid. This acid when in a separate state, or uncombined with other substances, always exists in the state of a gas. It is perhaps more widely diffused than any other gas or acid. It.is procured either by the direct combination of carbon with oxygen by combustion, or by expelling it from its natural union with lime by means of sulphuric acid.
Exp. Fill a bottle with oxygen gas and set it upright. Fasten a piece of charcoal of a cylindrical shape and two inches long, to a piece of wire, by winding the wire round one of its ends. Have the other end of the wire connected with the cork of the bottle. Ignite the lower end of the charcoal, and plunge it into the oxygen gas, putting the cork in its place. A vivid combustion of the charcoal will take place, attended with brilliant scintillations, affording a beautiful experiment.