The concentrated liquid Nitric Acid contains 1 atom of water, and has a sp. gr. of about 1·5; if perfectly pure, it is colourless, but usually it has a slight yellow tint, from partial decomposition into Peroxide of Nitrogen: it fumes strongly in the air.
The strength of commercial Nitric Acid is subject to much variation. An acid of sp. gr. 1·42, containing about 4 atoms of water, is commonly met with. If the specific gravity is much lower than this (less than 1·36), it will scarcely be adapted for the preparation of Pyroxyline. The yellow Nitrous Acid, so called, is a strong Nitric Acid partially saturated with the brown vapours of Peroxide of Nitrogen; it has a high specific gravity, but this is somewhat deceptive, being caused in part by the presence of the Peroxide. On mixing with Sulphuric Acid, the colour disappears, a compound being formed which has been termed a Sulphate of Nitrous Acid.
In the Appendix a Table is given which exhibits the quantity of real anhydrous Nitric Acid contained in samples of different densities.
Chemical Properties.—Nitric Acid is a powerful oxidizing agent (see [page 13]); it dissolves all the common metals, with the exception of Gold and Platinum. Animal substances, such as the cuticle, nails, etc., are tinged of a permanent yellow colour, and deeply corroded by a prolonged application. Nitric Acid forms a numerous class of salts, all of which are soluble in water. Hence its presence cannot be determined by any precipitating reagent, in the same manner as that of Hydrochloric and Sulphuric Acid.
Impurities of Commercial Nitric Acid.—These are principally Chlorine and Sulphuric Acid; also Peroxide of Nitrogen, which tinges the acid yellow, as already described. Chlorine is detected by diluting the acid with an equal bulk of distilled water, and adding a few drops of Nitrate of Silver,—a milkiness, which, is Chloride of Silver in suspension, indicates the presence of Chlorine. In testing for Sulphuric Acid, dilute the Nitric Acid as before, and drop in a single drop of solution of Chloride of Barium; if Sulphuric Acid be present, an insoluble precipitate of Sulphate of Baryta will be formed.
NITROUS ACID. See [Silver, Nitrite of].
NITRATE OF POTASH.
Symbol, KO NO5. Atomic weight, 102.
This salt, also termed Nitre, or Saltpetre, is an abundant natural product, found effloresced upon the soil in certain parts of the East Indies. It is also produced artificially in what are called Nitre-beds.
The properties of Nitrate of Potash are described as far as necessary at [page 190].