NITRIC ACID. 291 



or bard glass, at a red heat, and the red vapours condensed in 

 a receiver kept very cold by a freezing mixture. Oxygen gas 

 escapes during the whole process, the nitric acid of the nitrate 

 of lead being resolved into oxygen and peroxide of nitrogen ; 

 or NO 5 =NO 4 and O. As obtained by the last process, which 

 was proposed by Dulong, peroxide of nitrogen is a highly vo- 

 latile liquid, boiling at 82, of a red colour at the usual 

 temperature, orange yellow at a lower temperature, and 

 nearly colourless below zero, of density 1.451, and a white 

 solid mass at 40. It is exceedingly corrosive, and like 

 nitric acid stains the skin yellow. The red colour of its va- 

 pour becomes paler at a low temperature, but with heat in- 

 creases greatly in intensity, so as to appear quite opaque when 

 in a considerable body at a high temperature. It is the vapour 

 which Brewster observed to produce so many dark lines in the 

 spectrum of a ray of light which had passed through it (page 92.) 

 The peroxide is not decomposed by a low red heat, and appears 

 to be the most stable of the oxides of nitrogen. No compound 

 of it is known, unless peroxide of nitrogen be the radical, as 

 some suppose, of nitric acid. But Berzelius is inclined to con- 

 sider this oxide as itself a compound of nitric and nitrous acids, 

 for NO 5 + NO 3 =2NO 4 * 



The liquid peroxide of nitrogen is partially decomposed by 

 water, nitric oxide coming off with effervescence, and more and 

 more nitric acid being produced, in proportion to the quantity of 

 water added ; but a portion of the peroxide always escapes this 

 action, being protected by the nitric acid formed. In the pro- 

 gress of this dilution the liquid undergoes several changes of 

 colour, passing from red to yellow, from that to green, then 

 to blue, and becoming at last colourless. The peroxide of ni- 

 trogen is readily decomposed by the more oxidable metals, and 

 is a powerful oxidizing agent. 



NITRIC ACID. 



Syn. AZOTIC ACID (Thenard.) Eq. 677 ; NO 5 ; does not exist 

 except in combination. 



A knowledge of this highly important acid has descended from 

 the earliest ages of chemistry, but its composition was first 



* Trait^ de Chimie, par J. J. Berzelius, trad nit par B. Valerius, Bruxelles, 1838, 

 t. 1, p. 195. An excellent edition of the most valuable system of chemistry which 

 we at present possess. 



u 2 



