120 AZOTIC GAS. 



Analysis of 3. Nitrous acid is an orange coloured liquid, 

 acid. which may be obtained in a state of purity, by 

 exposing dry nitrate of lead to heat in a retort, 

 while the receiver is surrounded with a mixture 

 of snow and sak. It is a liquid, which, when 

 newly prepared, has an orange colour ; but I 

 have never been able to prevent it from acquir- 

 ing a green colour a change produced by the 

 absorption of a very small quantity of water. 

 This acid was first obtained in a separate state by 

 Berzelius Gay-Lussac first ascertained its na- 

 ture Dulong analyzed it, by passing it through 

 red hot copper wire. The oxygen united to the 

 copper, while the other constituent, the azote, 

 passed off in the state of gas. By this method 

 of proceeding, he obtained its constituents as 

 , follows : 



Azote 1-75 



Oxygen 4-1 78 



This is rather more than 4 atoms of oxygen 

 united to 1 atom of azote. But that the true 

 composition of nitrous acid, is 1 atom of azote 

 and 4 atoms of oxygen, is obvious from the fol- 

 lowing experiment, which I have often repeated. 

 Introduce into a cylindrical glass tube, 18 

 inches long and 0*9 inch in its internal diameter, 

 shut at one end, filled with water, and standing 

 inverted over a water trough, 100 volumes of 

 common air ; then let up to this air 100 vol- 



