of its oxygen, forming lower oxides of nitrogen, which impart a r>-d- 

 lii'ini'ii i-iifn//,' in it ; - ;;1 the pure arid is Colourless. 



Nitric acid, as an tn-i<l /tt/ilrittt\ enters into i-eaetions of doul>le 

 der( imp' >-it ion \\ith bases, Italic hydrates (alkalis), and with salts. In 

 all the.-se ca.-cs a >alt of nitric aeid is obtained. An alkali and nitric 

 acid :gi\e water and a salt : so, also, a basu- oxide \\ith nitric acid 

 gives a salt and water; for instance, K 1 1< ) -f 1 1 N< ) ;j = K N< ).,+ 1 1 ._,< >. 

 or with lime. CaO + i ) llN(.) : , = Ca( i N() 3 )., + lI 2 O. .Many of these salts 

 arc termed nitres/ 51 The composition of the ordinary salts of nitric- 

 acid may he expressed by the general formula M(N< ).,), where 31 

 indicates a metal replacing the hydrogen in one or several (K) equiva- 

 lents of nitric acid. We shall lind afterwards that the atoms M of 

 metals ai'e equivalent to one (^K, Na, ALC) atom of hvdrogen, or two 

 (I'a. .Mg. 1)U), or three (Al. In), or, in general, n atoms of hydrogen. 

 Th< .SV///N of 1/i/rif <iri<l are especially characterised by being all 

 xoluhli- In trutt-i-*' From the property common to all these salts 



"'" For technical and laboratory purposes recourse is frequently had to rat j n in /in/ 

 nit fir iirii] that is, the normal nitric acid, i I N( )-. containing lower oxides of nitrogen in 

 xJution. This acid is prepared hy decomposing nitre \vith half it- weight of strong sul- 

 phuric acid, or by distilling nitric acid \\ith an excess of sulphuric acid. The normal 

 nitric acid is iirst obtained, but it ]'artially decomposes, and gives the lower oxidation 

 products of nitrogen, which are dissolved by the nitric acid, to which they impart its 

 u>ual pale-brown or reddish colour. This acid fumes in the air. from which it attracts 

 moi-ture. forming a less volatile hydrate. If carbonic anhydride be pas-rd through the 

 red-brown fuming nitric acid tor a long period of time, especially if with the aid ot 

 n, i.iii rate heat, it expels all the lower oxido. and leaves a colourless acid free from these 

 oxide>. It i- necessary, in the preparation of the red acid, that the receivers should lie 

 kept quite cool, because it i- only \\hen cold that nitric acid is able to dissolve a large 

 proportion of the oxide- of nitrogen. The strong red fuming acid lias a specific gravity 

 r.'ii; at lit i . and ha-- a suffocating Mnell of the oxides of nitrogen. When the red acid is 

 mixed with water it turns green and then of a bluish colour, and \\ ith an excess of water 

 ultimateh becomes colourless. This i- owing to the fact that the oxides of nitrogen in 

 the pre-ence of water and nitric acid are changed, and give coloured solutions. 



'I'hr act ion of red fumin nitric acid lor a mixture with sulphuric acid 



Thus iron bee, ,1 ne-, CON e red uith a coating of oxides, and becomes insoluble in acids ; it 

 becomes, as I- -aid. passive. Tim- chromic acid land pota--mm dichromatel gives oxide 

 , ,i chromium in tin- red acid that is. it is deoxidised. This i- owing to the presence of 

 the lower oxides of nit i-o-en. which are capable of being oxidised that i-. of passing into 

 ,.;,! hfe the lirjher oxides. Hut. generally, the acti ...... f fuming nitric acid, both 



red and eoloiirle.- -. , . po v, ei'fu ! 1 \ oxidising. 



Ihdro-en i- not e\olved in the action of nitric acid (especially strong! on metals. 

 ,.\en uith tho-e metal- which e \ol\e hydrogen under the action of other acid-. 'I'll is is 

 |iecaii-i the li \drogei i at t he i ..... no it ol i t s sepa ra t ion reduces t he nitric acid, with forma- 



. ( 'ertain ba-ic alt o| nit ric acid. IK .u ever i for e\a mple. t he Ija^ic salt ol bi -mu tin. 

 are , iisolnble 111 wat ei\ v, 1 1 Ut. on the ot her i land, a 11 the normal -alt- are soluble, and 



- . itll , ,eept loiial phenomenon a! ...... _' acid-, becaii-e all the ordinar\ acid- form 



