953 



NITROGEN. 



NITROGEN. 



951 



process is decomposed by the heat as described above. Nitrite o^ 

 lead may be formed by heating metallic lead in a solution of the 

 nitrate of that metal. Nitrate of silver is thrown down as a white 

 precipitate on adding together solutions of nitrite of potash and nitrate 

 of silver ; it is soluble in hot water and crystallises out on cooling. 



4. Peroxide of nitrogen (NO,), was long supposed to possess acid 

 properties, and hence was called hyponitric acid and formerly nitroiis 

 acid. It may be obtained in the gaseous, liquid, or solid form. 



Gaseous peroxide of nitrogen is formed on mixing binoxide of nitrogen 

 with half its volume of oxygen in an exhausted receiver ; immediate 

 combination and condensation occur ; heat is evolved ; a red gas is 

 formed, which is the peroxide of nitrogen, and when this coloured gas 

 is subjected to a temperature of 0, it becomes liquid, and sometimes 

 solid. When also nitrate of lead is heated in a retort, it is decomposed, 

 and red vapour of peroxide of nitrogen is emitted, which is condensed 

 to the liquid state by being subjected to a freezing mixture. Towards 

 the latter part of the operation the compound comes over in the 

 anhydrous state, and may be obtained in crystals in a fresh, well-dried 

 and cooled, receiver. The slightest trace of moisture prevents the 

 formation of the crystals. Liquid peroxide of nitrogen is of a pale colour, 

 but becomes darker when heated ; it emits a very strong disagreeable 

 odour, and at a very moderate rise of temperature reassumes the 

 gaseous form. It is decomposed by water with strong effervescence, 

 being immediately separated into biuoxide of nitrogen, which is 

 evolved, and nitric acid, which remains in solution. 



Nitric acid (NO S ). Azotic acid. This important acid may be 

 formed by the direct combination of oxygen with nitrogen, or with 

 any of the other lower oxides of nitrogen ; by decomposition of ammo- 

 nia in presence of oxygen ; by the passage of electric sparks (for 

 example, lightning) through atmospheric air, or by the EREMAUCAUSIS 

 of organic bodies that contain nitrogen. In combination with bases 

 nitric acid is met with in nature in great abundance : it is rare to meet 

 with a specimen of rain-water that does not contain traces of nitrate of 

 ammonia ; most varieties of chalk contain a small quantity of nitrate 

 of lime, and in many tropical climates, especially some parts of India 

 and Peru, nitrates of potash and soda effloresce from the ground 

 during the dry seasons of the year. The production of these nitrates 

 is no doubt due to one, or a combination, of the causes already alluded 

 to so far as the nitric is concerned, while the several bases are always 

 at hand in the soil in the state of carbonates or other salts decom- 

 poaable by nitric acid. Native nitrate of potash constitutes the crude 

 nr taltpclre of commerce, and is the substance whence we derive 

 nitric acid itself, and most of the other nitrates. 



Ordinary liquid nitric acid was known so early as the 7th century ; 

 Raymond Lully obtained it from nitre ; Geber termed it tolutire water, 

 and Glauber manufactured it by the agency of sulphuric acid, in 

 precisely the manner adopted at the present day. Cavendish, however, 

 tirst made known its composition in 1785 [CAVENDISH, HEJJRY, in 

 Bioo. Div.], and our knowledge of it has since been perfected by Davy, 



monohydrated nitric acid then distils over, and is readily condensed, 

 while bisulphate of potash remains in the retort. The following 

 equation represents the decomposition : 



KO, NO, + 2(HO,S0 3 ) = KO.HO, 2S0 3 + HO, NO, 



Nitrate of 



l.'/t .-!.. 



Sulphuric acid. 



Bisulphate of 

 potash. 



Nitric acid. 



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 bisulyhate, 

 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 somewhat 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. V520. One hundred parts contain 

 65-72 of anhydrous nitric acid (NO,), and hence its composition is 

 expressed by the formula HO, NO.,. 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 

 (HO, 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 

 1-424 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 



name of aquafortis. It also becomes of the same colour when any 

 organic matter, such as a piece of straw or paper is allowed to fall 

 into it ; even mere exposure to sunlight will produce the same decom- 

 position. The chief cause of the instability of nitric acid is the 

 readiness with which it parts with a portion of oxygen ; indeed, as an 

 oxidising agent, it is in constant request by the chemist. Metals 

 thrown into it are rapidly converted into oxides with evolution of 

 binoxide of nitrogen and production of orange-red nitrous fumes, a 

 reaction taken advantage of in testing for the presence of nitric acid ; 

 sometimes the biuoxide of nitrogen is made to pass into solution of 

 protosulphate of iron, in which it dissolves with formation of a black 

 compound, a reaction that is even more delicate than that with the 

 copper turnings ; it is performed as follows. Into the liquid suspected 

 to contain nitric acid, or a nitrate, a few crystals of protosulphate of 

 iron are placed, and the whole is agitated for a minute or two to 

 facilitate the solution of a little of the salt ; strong sulphuric acid is 

 now cautiously poured down the sides of the vessel, and being heavy 

 flows on to the crystals at bottom, and at once gives rise to the black 

 compound iu question if a trace of nitric acid be present. The cause 

 of the production of the compound is the oxidation of a part of the 

 protosalt of iron to a persalt by the nitric acid, binoxide of nitrogen 

 being evolved, and combining with the undecomposed protosulphate ; 

 the use of the sulphuric acid is to liberate nitric acid from combina- 

 tion, and to facilitate the formation of the persulphate of iron. 



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, ail abridgement of 

 oue constructed by Dr. Ure : 



Anhydrous Nitric Add (N0 5 ). 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, 



AgO, NO, + Cl = AgCl + O 



Chlorine. 



Chloride 

 of silver. 



Oxygen. 



NO, 



Nitric 

 acid. 



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, deflagrate when thrown 

 on to ignited carbon, and are mostly soluble in water. 



Hydrides of nitrogen. Nitrogen united with two equivalents of 

 hydrogen forms the hypothetical substance amidugen, a body that 

 united with metals and electro-positive radicals, forms AMIDES. Nitro- 

 gen with three equivalents of hydrogen forms AMMONIA, and with four 

 equivalents the compound radical ammonium. 



Phosphide of Nitrogen (N 2 P). Dr. Pauli states (' Ann. 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 Nitroijen (NS,). 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, in inodorous and 

 has but little taste. 



Iodides of Nitrogen. [IODINE, nitrogen and.] 



Bromides of Nitrogen. [BROMINE, nitrogen and.] 



Chloride of Nitrogen. [CHLORINE, nitrogen and.] 



