BOG 



NITRIC ACID 



NITRIFICATION 



hut in that year Deville showed that Anhydrotu 

 Kitrir A fill, or Sitrie Anhydride, NtO, (see 

 NlTKiHJKX), might lx> obtained in transiwrent 

 colourles* crystals bv the action of perfectly dry 

 chlorine gas* on WHMfM crystals of nitrate of 

 silver, the reaction being exhibited in the iM|tiation : 



Kluw (!.. Cklurlo.. Cblortd. 8ll.r. SlUte Aohjdrtd.. Oiwo- 



2AgNO, + Cl, = 2AgCl + N,0, + O 

 It is a very unstable compound, and sometime* 

 explode* spontaneously. It dissolves in water with 

 evolution of much heat, and forms hyclrated nitric 

 acid. Nitric Acid (sym. HNO S ; equiv. 03: sp. gr. 

 1530), when perfectly pure, is a colourless, limpid, 

 fuming, powerfully caustic fluid, possessing an 

 intensely acid reaction, as shown by its action on 

 litmus. It boils at 187 (86 3 C.). It parts very 

 readily with a portion of its oxygen to most metals, 

 and hence is used in the lalx>ratory as an oxid- 

 ising agent. Whether in the concentrated or in a 

 more dilute form, it acts energetically on organic 

 matters. As examples of such actions we may 

 refer to it* power of decolorising indigo; of stain- 

 ing the skin and all albuminous tissues of a bright- 

 yellow colour ; of coagulating fluid albumen ; and 

 of converting cotton fibre into an explosive sub- 

 stance (see GUN-COTTON). The applications of 

 this acid in the arts, in manufactures, and in 

 chemical processes are very extensive. 



The concentrated nc-id, UNO,, is by no means a 

 stable compound. If it be exposed to the action of 

 light it is decomposed with the formation of lower 

 oxides of nitrogen ; and mere distillation produces 

 a similar effect. When it is mixed with water it 

 emits a sensible amount of heat, owing to the 

 formation of a much more stable hydrate, 2HNO,+ 

 3H,0, which distils at 250" (121 C.) without 

 change, and is unaffected by exposure to light. 

 It- specific gravity is P424 ; and it is found that a 

 weaker acid when heated parts with its water, and 

 a stronger acid with its acid, till each arrives at 

 this density. The existence of this hydrate has, 

 however, lieen called in question by Koscoe. The 

 so-called Fuming Xitric Acid is merely a mixture 

 of the pure acid with one of the lower oxides. 



Nitric acid does not occur naturally in a free 

 state ; but it is found tolerably abundantly in com- 

 bination with potash, soda, linfe, and magnesia; and 

 after thunderstorms traces of it, in combination 

 with ammonia, are found in rain-water. It may- 

 be formed in small quantity by passing a series of 

 electric sparks through a mixture of its component 

 gases in the presence of water, which is a mere 

 imitation, on a small scale, of the mode in which 

 it is nrodnced in the atmosphere by a storm. It is 

 DMMUf pmmd in the laboratory by the applica- 

 tion of heat to a mixture of equal weights of 

 powdered nitre (nitrate of potash) and oil of vitriol 

 (hydrated sulphuric acid) placed in a retort. A 

 combination of sulphuric acid and potash remains 

 in the retort, while the nitric acid uistils over, and 

 is condensed in the receiver, which is kept cool by 

 the application of a wet doth. The reaction is 

 explained by the equation : 



Hltn. Holphnrtc Acid. Nitric Acid. Btral|>hti of Potuh. 



KNO, + HjSO, = HNO, + KHSO 4 



During distillation red fumes appear, arising from 

 the decomposition of a portion of the nitric acid and 

 formation of some of the lower oxides of nitrogen. 

 In this operation lirn equivalents of oil of vitriolare 

 taken for one of nitre, these being the proportions 

 found by experience to le most suitable. If they 

 are taken equivalent for equivalent, a very impure 

 red fuming acid is the result. In the manufacture 

 of nitric acid on the large scale the glass retort is 

 replaced by a cast-iron cylinder coated with lire 

 clay, and the receiver by a scries of earthen con 

 duiising vesaeU connected by tubes ; and nitrate of 



soda (f>ee NlTRE) is substituted for nitre, in conse- 

 i| ill-lire of its being a cheaper salt, and of its con- 

 Uininj; 9 per cent, more nitric acid. 



Nitric acid combines with liases to form niirnlet, 

 some of which, as those of potash, soda, oxide of 

 ammonium, silver, &r., are anhydrous, while others 

 combine with a certain numlx-r (often six ) of equiva- 

 lents of water of crystallisation. Most of them are 

 M.liiMe in water, crystallisable, ami readily fusible 

 by heat ; and at an elevated temperature they are 

 all decomposed, usually leaving only the oxide of 

 the metal. If pa|er lie soaked in a solution of a 

 nitrate, allowed to dry, ami ignited, it burns in the 

 smouldering mode characteristic of ti.m-li /mjier. 

 This pro|erty is, however, share;! by other salt*. 



The test- for this acid when it is present in small 

 quantities are less satisfactory than those for the 

 other ordinary mineral acids. All its MflJpOUBdi 

 are so soluble that no preri/iitant for this acid is 

 known. The test method for its detection is 

 mixing the fluid to be tested with a solution of 

 sulphate of iron, and then carefully pouring sul- 

 phuric acid through a tube to the Imttom of the 

 glass so as to form a lower layer. If much nitric 

 acid is present a black colour is produced ; if only 

 a small quantity is present the liquid Wnnies 

 reddish brown or purple ; the dark colour licing 

 due to the formation of nitric oxide by the de- 

 oxidising action of a portion of the iron salt on the 

 nitric acid. 



Medicinal Uses. In the British pharmacopoeia 

 there is both a strong and a dilute acid. The 

 stiong acid has a specific gravity of P42, contains 

 70 per cent, of real acid, HNO S , while the diluted 

 acid is prepared by mixing six ounces of the former 

 with aliout twenty-five of distilled water, and has 

 a specific gravity of 1-101. The dilute acid is used 

 internally as a tonic in conjunction with bitter in- 

 fusions. ' In many cases of bilit.usm-ss. of chronic 

 inflammation of die liver, and in syphilitic cases in 

 which mercurials are inadmissible, it may be pre- 

 scribed with great lienelit. either nlone or in conjunc- 

 tion with hydrochloric acid, externally as a bath or 

 lotion, or internally in doses of about 20 minims 

 properly diluted. The strong acid is useful as an 

 escharo'tic ; e.g. to destroy warts, some kinds of 

 polypi, the unhealthy tissue in sloughing ulcers, 

 \c., and as an application to parts bitten uy rabid 

 or venomous animals. Largely diluted as 50 or 

 60 drops of the strong acid to a pint or more of 

 water it forms a stimulative application for torpid 

 ulcers. 



Nitrification is the changing of nitrogenous 

 organic matter or ammonia compounds into nitrates. 

 I'o-sihly the nitrogen of the air under certain ci ion m- 

 st.-iiu -es 'also undergoes this change in soils. Some 

 authorities ascriln- the change to ' a ferment," 'an 

 organised structure,' the ' micrococcus nitrificans,' 

 &c., but it is a power possessed possibly by many 

 micro-organisms. These nitrifying liacteroids JHT- 

 form their work under certain conditions. First, 

 the temperature must be suitable, for at about 

 5 C. the process is stopped ; but with a rise of 

 temperature there is a proportionate increase of 

 work commencing at aiKiut 12 C. until 37 is 

 reached, which is the 'optimum' temperature, and 

 from this onwards there is a diminution of action 

 until the 'maximum' temperature of 66 C. is 

 reached, when nitrification ceases. These Imcter- 

 oids are annihilated at a temperature of 90 C., 

 although the same result will follow drying even 

 at a much lower temperature. The second condi- 

 tion is the presence of oxygen ; and the third is 

 the presence of a salifiable base, such as lime, 

 potash, soda, &c., without which nitrification 

 cannot proceed. Under these conditions nitrifi- 

 cation goes on in every fertile soil, the atmospheric 

 nitrogen, nitrogenous organic matter, or ammonia 



