Nitric acid is one of the most corrosive substances known ; it per manently stains the cuticle of a yellow colour, and in a similar way attacks wool, feathers, and all animal matters that contain albumen. Its strength is most readily ascertained by taking its specific gravity, and then consulting such a table as the following, an abridgement of one constructed by Dr. Ure Anhydrous Nitric Acid This was first obtained in brilliant, colourless, transparent, prismatic crystals, by M. Deville. The method of operating consists in passing a slow current of perfectly dry chlorine gas over pure crystals of nitrate of silver heated in an oil bath, and connected with a receiver made cool by a freezing mixture. The de composition that takes place is thus expressed,— On the large scale, nitrate of soda (Chili saltpetre) is used in the place of nitrate of potash, and the process is conducted in capacious iron cylinders, coated on the upper part of the inner surface with fire-clay, to prevent the action of the nitric fumes upon the metal. Manufacturers use the soda nitrate, because it is cheaper than the potash salt, contains nine per cent. more acid, and is decomposed at a lower temperature, thereby enabling a saving in fuel to be effected. Iron retorts are used in the place of glass or earthenware, because the salt left in them can be a neutral sulphate, instead of a bisulphate, thus admitting of the use of one-half the quantity of sulphuric acid that otherwise would be necessary. Neutral sulphate of potash or of soda is, however, exceedingly hard, and being but sparingly soluble in water, has to be detached from vessels containing it by the use of iron tools, a proceeding somewhit hazardous if those vessels are of glass or earthenware.
As obtained by the above process, nitric acid is a colourless, transparent liquid, of sp. gr. 1.520. One hundred parts contain 8512 of anhydrous nitric acid (NO,), and hence its composition is expressed by the formula HO, It boils at 184° Fahr., and freezes at — 40'. Exposed to the air it continues to fume very strongly until it has absorbed sufficient water to constitute it a terhydrate (110, NO.+ 3 Aq.) : this is the condition of maximum stability of
aqueous nitric acid ; a weaker acid loses water on boiling until the state of terhydrate is reached, a stronger acid losing nitric acid under the same circumstances. Terhydrated nitric acid has a sp. gr. of contains sixty per cent. of anhydrous acid, and boils at 250° Fahr. Nitric acid readily absorbs the lower gaseous oxides of nitrogen, forming a yellow, or even red, fuming liquid, known by the In order to ensure success a number of precautions must be ob served, for which see M. Deville's paper (` Ann. de Chimie; III , xxviii. 241).
Nitrates. Salts formed by the union of nitric acid with a base ; the number of equivalents of each being usually equal, never containing more acid than base, but frequently more base than acid. They are nearly all decomposed when strongly heated, dellagrate when thrown on to ignited carbon, mostly soluble in water.
Hydrides of Ititro&en. Nitrogen united with twa equivalents of hydrogen forms the hypothetical substance amidogen, a body that united with metals and electropositive radicals, forms AMIDES. .Nitro geu with three equivalents of hydrogen forms AMMONIA, and with four equivalents the compound radical ammonium.
Phosphide of Nitrogen (N„P). Dr. Pauli states (‘ Aim. der Chem. u. Pharm.,' ci. 41), that when an intimate mixture of pentasulphide of phosphorus and chloride of ammonium is distilled, a light powder of slightly yellow colour is obtained as a residue, which is phosphide of nitrogen, It is insoluble in water and nitric acid, and when melted with potash evolves ammonia.
Sulphide of Nitrogen A compound formed by the re-action of protochloride of sulphur, ammonia and water. It exists in two isomeric states ; in the one it is of a light green colour, in the other it is yellow. It crystallises from solution in hot ether, is inodorou,s and has but little taste.
Iodides of Nitrogen. [IODINE, nitrogen and.] Bromides of Nitrogen. [BROMINE, nitrogen and.] Chloride of Nitrogen. [CHLORINE, nitrogen and.]