_Chemical properties._--Nitric acid is a powerful oxidizing agent; 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 color, 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 re-agent, 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, Nitrate of.) Nitrate of Potash. Symbol, KO NO{5}. 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. Nitrate of potash is _an anhydrous salt_,--it contains simply nitric acid and potash, without any water of crystallization; still, in many cases, a little water is retained mechanically between the interstices of the crystals, and therefore it is better to dry before use. This may be done by laying it in a state of fine powder upon blotting-paper, close to a fire, or upon a heated metallic plate. Nitrate of Baryta. Symbol, BaO NO{5}. Atomic weight, 131. Nitrate of baryta forms octahedral crystals, which are anhydrous. It is considerably less soluble than the chloride of barium, requiring 12 parts of cold and 4 of boiling water for solution. It may be substituted for the nitrate of lead in the preparation of protonitrate of iron. Nitrate of Lead. Symbol, PbO NO{5}. Atomic weight, 166. Nitrate of lead is obtained by dissolving the metal, or the oxide of lead, in _excess_ of nitric acid, diluted with 2 parts of water. It crystallizes on evaporation in white anhydrous tetrahedra and octahedra, which are hard, and decrepitate on being heated; they are soluble in 8 parts of water at 60°. Nitrate of lead forms with sulphuric acid, or soluble sulphates, a white precipitate, which is the insoluble sulphate of lead. The _Iodide_ of lead is also very sparingly soluble in water. Nitrate of Silver. (_See_ Silver, Nitrate of.) Nitro-Hydrochloric Acid. Symbol, NO{4} + Cl.