x NITRE, NITRIC ACID, AND NITROGEN 197 



Gay-Lussac believed that these should be taken as round 

 numbers and concluded that 100 parts of oxygen combine 

 with 2w parts of nitrous gas to form 100 parts of the brown 

 fumes. 



It is now known that the relative volume of the product 

 varies very greatly with the temperature ; at temperatures 

 above 150 C. 200 volumes are produced, but at atmospheric 

 temperatures the quantity may be only a little above 100 

 volumes. The gas resulting from the admixture is now 

 called NITROGEN PEROXIDE. Since it is formed by the com- 

 bination of one volume of oxygen with two volumes of nitric 

 oxide (containing i volume oxygen and i volume nitrogen) 

 it follows that nitrogen peroxide is a compound of nitrogen 

 with oxygen in the ratio of one volume of nitrogen to two 

 volumes of oxygen. 



C. NITRIC AND NITROUS ACIDS. 



Two varieties of nitric acid. Although Cavendish had 

 discovered in 1784 the nature of the characteristic con- 

 stituents of nitric acid, it was not until 1816 that the 

 quantitative composition of the acid was finally determined. 

 This delay was due, mainly, to the fact that the name was 

 applied to acids which varied widely in composition and 

 properties. 



During the earlier alchemistic period nitric acid was pre- 

 pared by throwing a mixture of green vitriol and nitre into 

 a retort or on a charcoal fire and condensing the brown 

 fumes in a receiver containing cold water. In this way a 

 red, fuming acid was produced. 



On the other hand, the acid which Glauber prepared by 

 distilling saltpetre with oil of vitriol in glass vessels at a low 

 temperature was almost colourless. But it was not possible 

 to distinguish the two varieties sharply from one another, 

 and the whole range of acids, from the least to the most 

 highly coloured, were described under a single name as 



