Acids. 155 



the heat, the elastic fumes again arise. The more 

 water we add to these acids, the more we de- 

 press their volatility: they may, when diluted, 

 be concentrated, but not so much as the sul- 

 phuric. 



The nitric acid, which is a combination of 

 nitrogen or azote (the impure part of our at- 

 mosphere) with oxygen, in the proportion of 

 thirteen parts of nitrogen to eighty-seven of oxy- 

 gen, is a fluid of considerable weight, but not 

 quite so heavy as the sulphuric. In its strongest 

 state it is white, but the action of light by de- 

 veloping some nitrous gas gives it an orange co- 

 lour, and then, when exposed to the air, it con- 

 stantly emits fumes, the quantity of acid it con- 

 tains being greater than the water can repress, 

 and these fumes are noxious. Itjlames with oil 

 of turpentine. In this experiment, add a little 

 sulphuric to the nitrous acid, which increases its 

 effects. Many other oils would succeed without 

 the sulphuric acid, as oil of cloves. The acid 

 ought to be recent, for if long kept, or in bottles 

 not tight, it loses its power. 



The nitric acid emits fumes which tinge the air 

 with the same colour[as itself, especially the air in 

 the bottle with it. It readily attracts water from 

 the air; but when the water is added in any 

 quantity they unite with violence, producing 

 heat and copious fumes. The colour of the acid 

 is changed to a green, and sometimes to a blue, 

 and upon the addition of more water, the oreen 



