_Uses._ Nitric acid is employed in assaying, in dyeing, in etching on copper, in the preparation of gun-cotton, oxalic and sulphuric acids, &c.
In medicine it is used as a caustic to corns and warts; and in doses of 1 to 10 drops, in a tumbler of water, in liver complaints, fevers, dyspepsia, syphilis, to remove the effects of mercury, or as a substitute for that drug, &c. Externally, it is employed in the form of baths, lotions, and ointment. Dr Collier states that a strong lotion of nitric acid is almost a specific in lepra, and several other kindred skin diseases.
_Concluding Remarks._--The common source of nitric acid is nitrate of potassium, but it may also be obtained from other nitrates by a similar process. Nitrate of sodium is frequently used instead of nitrate of potassium, and is more convenient in some respects, as the residuum is more easily dissolved out of the retort or cylinder. The residuum of the common process with nitre ('sal enixum') is chiefly employed as a flux by the glass-houses, and as a source of potash in the manufacture of alum.
By proper management nitre yields more than 2/3 of its weight of pure nitric acid, sp. gr. 1500; and nitrate of soda, its own weight of acid, sp. gr. 14.
By the patent process of M. Mallet, dried nitrate of soda is decomposed by dried or monohydrated boracic acid, by heating the two together. The products are liquid nitric acid, which distils over, and biborate of soda (borax), which remains in the retort.
The crude coloured nitric acid of commerce (aquafortis) was originally prepared by distilling a mixture of nitre and copperas, and is still sometimes obtained in this way.
The nitric acid of commerce may be freed from the impurities alluded to above by one or other of the following methods:--
1. By the addition of a little nitrate of silver, as long as it produces any cloudiness, and, after repose, decanting the clear acid, and rectifying it at a heat under 212. To ensure a perfectly colourless product, a small portion of pure black oxide of manganese should be put into the retort. (Murray.)
2. By agitating the acid with a little red oxide of lead, and then rectifying it, as before.
3. By adding 1% of bichromate of potassa to the acid before rectifying it.
This answers well for acid not stronger than sp. gr. 148.
4. By rectification at a gentle heat, rejecting the first portion that comes over, receiving the middle portion as genuine acid, and leaving a residuum in the retort. (Ure.)
According to Apjohn and others, the strongest liquid nitric acid, sp. gr.
1520, is a monohydrate; that of the sp. gr. 1500, a sesquihydrate; that of 1486, a binhydrate; and that of 1244, a quadrihydrate; or containing respectively 1, 1-1/2, 2, and 4 atoms of water. (See _below_.)
=Nitric Acid, Anhy'drous.= N_{2}O_{5}. _Syn._ NITRIC ANHYDRIDE. This interesting substance was first obtained in a separate form by M. Deville, in 1849.
_Prep._ (M. Deville.) Nitrate of silver is dried by exposure to a current of dry carbonic acid at a temperature of 356 Fahr., and the tube containing it is then immersed in a water bath heated to 203 Fahr.; pure dry chlorine gas is next passed through the apparatus, and, as soon as the reaction commences, the temperature is retraced to 154 or even 136, but not lower; the production of crystals in the receiver, which must be cooled by a powerful freezing mixture, soon commences; lastly, the liquid portion of the product is removed by a current of dry carbonic-acid gas.
_Prop., &c._ Colourless prismatic crystals, which melt at 86 Fahr., boil at about 115, and at 122 begin to suffer decomposition; added to water, much heat is generated; it rapidly attacks organic bodies, even caoutchouc; sometimes it explodes spontaneously. The process for its preparation is tedious and difficult.
=Nitric Acid, Dilute.= ACIDUM NITRICUM DILUTUM (B. P., Ph. L., E., & D.), L. _Prep._ 1. (Ph. L.) Nitric acid (sp. gr. 142), 3 fl. oz.; distilled water, 17 fl. oz.; mix. Sp. gr. 1082. "1 fl. oz. is saturated by 154 gr.
of the crystals of carbonate of soda." It contains about 12% of pure anhydrous acid.
2. (Ph. E.) Nitric acid (1500), 1 fl. oz.; distilled water, 9 fl. oz. Or, commercial nitric acid (1390), 1 fl. oz. 5-1/2 dr.; water, 9-1/2 fl. oz.
Sp. gr. 1077. It contains 1116% of pure dry nitric acid.
3. (Ph. D.) Nitric acid (1500), 4 fl. oz.; water, 29 fl. oz. Contains about 97% of pure acid. The above are used for convenience in dispensing.--_Dose_, 15 drops to 1/2 fl. dr., or more. The above must not be confounded with the acidum nitricum dilutum, Ph. D. 1826, which had the sp. gr. 1280, nor with the following:--
4. (Henry's.) Sp. gr. 1143; equal in saturating power to hydrochloric acid sp. gr. 1074, and sulphuric acid 1135. Used in assaying.
5. (B. P.) Nitric acid, 6; distilled water sufficient to make the mixture when cooled to 60 Fahr., measure 31. Contains 15 per cent. of anhydrous nitric acid. _Test._ Sp. gr. 1101. Six fluid drachms (3613 grains) by weight require for neutralisation 1000 grain measures of the volumetric solution of soda, and, therefore, contain exactly one equivalent in grains of anhydrous acid, namely, 54 gr.--_Use._ Tonic, astringent, lithonlytic.--_Dose_, 10 to 30 minims.
=Nitric Acid, Fuming.= _Syn._ NITROUS ACID; ACIDUM NITRICUM FUMANS, L.
The red fuming nitrous or nitric acid of commerce is simply nitric acid loaded with nitric peroxide (which _see_). That of the Ph. Bor. is distilled from nitre, 2 parts; oil of vitriol, 1 part.
=NI'TRIC ANHY'DRIDE.= See NITRIC ACID, ANHYDROUS.
=NI'TRIC OXIDE.= See NITROGEN, OXIDES OF.
=NI'TRITE.= A salt of nitrous acid; _e.g._ KNO_{2}, nitrite of potassium.
=NITRO-BEN'ZOL.= C_{2}H_{5}NO_{2}. _Prep._ By treating benzol with strong fuming nitric acid, with heat; after the violence of the reaction is over, the liquid is diluted with water, and the heavy oily fluid which separates is collected, washed, and dried.
_Prop., &c._ Yellowish, very sweet; smells of bitter almonds; insoluble in water; little affected by reagents; boils at 415 Fahr.; sp. gr. 1209.
Heated with an alcoholic solution of caustic potassa, and the mixture submitted to distillation, it yields a red, oily liquid, from which large red crystals of azobenzol separate. These are nearly insoluble in water, freely soluble in alcohol and ether, melt at 149 Fahr., and boil at 5594 Fahr. BINITROBENZOL is made by dissolving benzol in a mixture of equal volumes of the strongest nitric and sulphuric acids, and boiling the liquid for a few minutes; the crystals (dinitrobenzol) which form as it cools are insoluble in water, but are freely soluble in alcohol.
Nitro-benzol is extensively used as a substitute for the essential oil of bitter almonds, in perfumery. It is very poisonous, a quality, which Letheby asserts, it acquires owing to its conversion in the animal economy into aniline. M. Ferrand states that the presence of nitro-benzol in essence of bitter almonds may be detected as follows:--Heat to ebullition, in a test tube, three or four c.c. of a 20 per cent. alcoholic solution of potash, together with ten drops of the suspected essence. If nitro-benzol be present, the mixture takes a red colour; if the essence of bitter almonds be pure, it becomes a pale straw colour.
=NI'TROGEN.= N. _Syn._ AZOTE; NITROGENIUM, AZOTUM, L. A gaseous elementary substance, discovered by Rutherford, in 1722, and found to be a constituent of the atmosphere by Lavoisier, 1755. It is found both in the organic and inorganic kingdoms of nature; it forms about 4/5, or 78% of the bulk of the atmosphere, enters largely into the composition of most animal substances, and is a constituent of gluten, the alkaloids, and other vegetable principles.
_Prep._ 1. A small piece of phosphorus is placed in a capsule floating on the surface of the water of the pneumatic trough, and after setting it on fire a gas or bell-jar is inverted over it; as soon as the combustion is over, and the fumes of phosphoric anhydride have subsided, the residual gas is washed by agitation with recently boiled distilled water, or with a solution of pure potassa. It may be dried by either letting it stand over fused chloride of calcium, or, what is better, by passing it through concentrated oil of vitriol.
2. A porcelain tube is filled with copper turnings, or, preferably, with spongy copper (obtained by reducing the oxide with hydrogen), and is then heated to redness, a stream of dry atmospheric air being at the same time directed through it. By repeating the process with the same air, and finally passing it over fragments of pumice moistened with strong solution of potassa to absorb carbonic anhydride, the product is rendered quite pure.
3. Chlorine gas is passed into a solution of pure ammonia, care being taken to employ a considerable excess of the latter; the evolved gas, after being dried, is pure nitrogen. There is some danger of producing the explosive compound, chloride of nitrogen, with this process.
4. (Corenwinder.) From solution of nitrate of potassium, 1 volume; concentrated solution of chloride of ammonium, 3 vols.; gently heated together in a flask, and the evolved gas passed through sulphuric acid.
Pure.
5. By boiling a solution of nitrite of ammonium, or, which amounts to the same thing, a mixture of one measure of a solution of nitrite of potassium and three measures of a solution of chloride of ammonium. Both solutions must be concentrated. This is the easiest method of preparing nitrogen and of obtaining the gas in a pure state.
_Note._--The nitrite of potassium to be employed in this process is best prepared by passing nitrous anhydride, evolved from starch and nitric acid, into a solution of potassa (sp. gr. 138) till it imparts an acid reaction to test-paper, and then neutralising by the addition of potassa.
6. From lean flesh digested in nitric acid, at a gentle heat.
_Prop., &c._ Pure nitrogen is a colourless, odourless, tasteless gas, neither combustible nor capable of supporting combustion or respiration.
It is neutral to test-paper, does not affect lime water, and is only slightly absorbed by pure water. Its sp. gr. is 9713. It is recognised by its purely negative qualities.
=Nitrogen, Chlo"ride of.= NCl_{3}. _Syn._ NITROGEN TRICHLORIDE, TERCHLORIDE OF NITROGEN. This compound was discovered by Dulong in 1811, but its nature was first accurately determined by Sir H. Davy.
_Prep._ (Liebig.) Dissolve chloride of ammonium, 1 oz., in hot water, 12 or 14 oz., and as soon as the temperature has fallen to 90 Fahr., invert a wide-mouthed glass bottle full of chlorine over it. The gas is gradually absorbed, the solution acquires a yellowish colour, and in the course of 15 to 20 minutes yellow, oil-like globules of chloride of nitrogen form upon the surface of the liquid, and ultimately sink to the bottom. The globules, as they descend, should be received in a small leaden saucer, placed under the mouth of the bottle for the purpose.
_Prop., &c._ Chloride of nitrogen should consequently be only prepared in very small quantities at a time. Both its discoverer and Sir H. Davy met with severe injuries while experimenting on it. Its sp. gr. is 1653; it volatilises at 160 Fahr., and between 200 and 212 fulminates violently.
Contact with combustible bodies at ordinary temperatures immediately causes detonation. _The explosive power of this compound seems to exceed that of every known substance, not even excepting fulminating silver:_ A minute globule, no larger than a grain of mustard seed, placed on a platina spoon, and touched with a piece of phosphorus stuck on the point of a penknife, immediately explodes, and shivers the blade into fragments, at the same time that the vessel that contains it is broken to pieces. Olive oil, naphtha, and oil of turpentine, have a similar effect.
See NITROGEN, IODIDE OF (_below_).
=Nitrogen, I'odide of.= NI_{2}. _Syn._ NITROGEN TRI-IODIDE, TERIODIDE OF NITROGEN. A dark brown or black insoluble powder, which is most safely and conveniently prepared by saturating alcohol (sp. gr. 852) with iodine, adding a large quantity of the strongest pure solution of ammonia, and agitating the mixture; water must now be added, when iodide of nitrogen will be precipitated, and must be carefully washed with cold distilled water. The filter containing the precipitate should be spread out on a sheet of glass and torn into small pieces while the iodide is still moist.
The precipitate should be simply exposed to air only.
_Prop., &c._ It detonates violently as soon as it becomes dry, by the slightest pressure or friction, even that of a feather, and often spontaneously; but this explosion is scarcely so powerful as that of the chloride of nitrogen. It also explodes whilst moist, though less readily.
It should only be prepared in very small quantities at a time. Recent researches induce the belief that both the above compounds contain hydrogen.
=Nitrogen, Ox'ides of.= Nitrogen forms 5 distinct compounds with oxygen.
1. =Nitrous ox'ide.= _Syn._ PROTOXIDE OF NITROGEN; LAUGING GAS; NITROGENII PROTOXYDUM, L. _Prep._ From fused nitrate of ammonium, introduced into a glass retort, or a flask furnished with a bent tube, and then exposed, over a spirit-lamp, or charcoal-chauffer, to a temperature of about 389 Fahr.; the evolved gas may be collected in bladders, gas-bags, a gasometer, or in the pneumatic trough over warm water. The gas may be purified by pouring it through three wash-bottles, one containing water, one a solution of sulphate of iron, and the other a solution of potassa.
_Prop., &c._ Colourless; possesses an agreeable odour, and a sweetish taste; at 32, under a pressure of 30 atmospheres, it is liquid; this, when exposed under the receiver of a powerful air-pump, changes into a snow-like solid; at -180 Fahr., it is a transparent, colourless, crystalline body; it supports combustion, and is absorbed by cold water.
Sp. gr. 1520. Its most remarkable property is its action on the system when inspired. A few deep inspirations are usually succeeded by a pleasing state of excitement, and a strong propensity to laughter and muscular exertion, which soon subside, without being followed by languor or depression. Its effects, however, vary with different constitutions. From 4 to 12 quarts may be breathed with safety. It produces temporary insensibility to pain, like chloroform or ether; but its use is dangerous when affections of the heart, lungs, or brain are present. This gas is now successfully and extensively employed as an anaesthetic in dental surgery.