NITRIC ACID exists, in combination with the bases, potash, soda, lime, inao , nesia, in both the mineral and vegetable kingdoms. This acid is never found in sulated. It was distilled from saltpetre so long ago as the 13th century, by ignit ing that salt, mixed with copperas or clay, in a retort. Nitric acid is generated when a mixture of oxygen and nitrogen gases, confined over water or an alkaline solution, has a series of electrical explo sions passed through it.
This acid is a compound of 1 atom or equivalent of nitrogen =14, and 5 of oxy gen (8 X 5) = 40 ; hence its equivalent in the dry or anhydrous state, as it exists, for instance, in nitre, is 14 + 40 = 54. As it usually occurs in the liquid state, it is a compound of 1 equivalent of dry acid, 54,. and 2 of water (9 X 2), 18; hence the i equivalent of the liquid acid is 72. It is commonly known in commerce under the name of aqua fortis, and is prepared by distilling a mixture of sulphuric acid and nitre. It is commonly yellow, or even deep orange colored • but it may be de prived of nitric oxide, which occasions this color, by heat, and is then colorless. It is intensely corrosive and sour, fumes when exposed to air, and has a specific gravity of 1.50 when in its utmost state of concentration. It boils at 248', and freezes at —50°. It is a most powerfully oxidizing agent, and is decomposed with more or less rapidity by almost all the metals.
The salts which it forms are called ni trates; they are all soluble in water ; they are decomposed by heat, and, when mix ed and gently heated with sulphuric acid, they evolve nitric or nitrous acid.
On the small scale nitric acid may be made by heating together nitrate of pot ash and diluted oil of vitro] in atomic pro portions : a receiver or flask should be attached to the tube of the retort and kept cool by immersion in water. Cold should also be applied to the neck of the retort. When the mixture begins to boil, red fumes come off, which cease after awhile, and reappear at the close of the process. To obtain a pure acid it is ne cessary to change the receivers and reject the first and last portions of the distilla tion, which contain the nitrous acid fumes, chlorine, and perhaps, sulphuric acid. That which distills over, when pure, is the concentrated acid having a density of 1.492.
On the large scale, iron-retorts are used similar to them, in which hydrochloric acid is obtained.
Nitrate of soda is now generally used in place of nitre, as affording more acid and being a cheaper salt. The acid ob tained thus contains a nitrate of iron, and requires redistillation before it can be gotten rid of. Nitric acid, of a density of 1.47, may be had, colorless ; but when farther concentrated, it is partially de composed ; whereby some nitrous acid is produced, which gives it a straw-yellow tinge. At this strength it exhales white or orange fumes, which have a peculiar, though not very disagreeable smell ; and even when largely diluted with water, it tastes extremely sour. The greatest den sity at which it can be obtained is 1.51 or perhaps 1.52, at 60° F. in which state, or even when much weaker, it powerfully corrodes all animal, vegetable, and most 'W metallic bodies. hen slightly diluted it is applied, with many precautions, to silk and woollen to stain them of a bright yellow hue.
In the dry state, as it exists in nitre, this acid consists of 26.15 parts by weight of azote, and 73.85 of oxygen ; or of 2 volumes of the first gas, and 5 volumes of the second.
When of specific gravity 1'5, it boils at about 210° Fahr. ; of 1.45, it boils at about 240° ; of 1.42, it boils at ; and of P40, at 246° F. If an acid stronger than 1•420 be distilled in a retort, it gradually be comes weaker ; and if weaker than 1'42, it gradually becomes stronger, till it as sumes that standard density. Acid of specific gravity 1.485 has no more action upon some metals, as tin, than water has, though when either stronger or weaker it oxidizes it rapidly, and evolves fumes of nitrous gas with explosive violence. Acid of 1-420 consists of 1 atom of dry acid, and 4 of water ; acid of P485 of 1 atom of dry acid, and 2 of water ; the lat ter compound possesses a stable equili brium as to chemical agency ; the former as to calorific. Acid of specific gravity I•884, consisting of 7 atoms of water, and 1 of dry acid, resists the decomposing agency of light. Nitric 'acid acts with great energy upon most combustible sub stances, simple or compound, giving up oxygen to them, and resolving itself into nitrous gas, or even azote. Such is the result of its action upon hydrogen, phos phorus, sulphur, charcoal, sugar, gum, starch, silver, mercury, copper, iron, tin, and most other metals.