460 NITROUS ACID. 



(e.) Action of water. To form liquid nitrous acid, nothing more 

 is necessary than to add this vapor to water mixed with a large 

 quantity of this fluid, it becomes nitric acid, which remains colorless 

 in the water, while a quantity of nitric oxide gas escapes into the air, 

 producing the usual red fumes. 



But if the nitrous acid is added to a very little water, the gas is 

 retained and the fluid becomes green ; with an intermediate quantity of 

 water, the anhydrous nitrous acid, when dropped in, emits at first, a 

 considerable quantity of red fumes, which however diminish as more 

 acid is added, and finally cease. 



In the progress of the addition of the acid to the water, (as has 

 been already stated under the hypo- nitrous acid,) the liquid passes 

 through shades of greenish blue, and green of various tints, and be- 

 comes at length, orange yellow, which is the color of the acid itself. 

 These changes of color are evidently owing to a mixture of differ- 

 ent proportions of the three acids, and of the nitric oxide.* 



(f.) Action on animals; highly irritating and suffocating in 

 the glottis ; it should be avoided as much as possible. In the nu- 

 merous experiments of the laboratory, in which nitrous vapors are dis- 

 engaged, it sometimes produces permanent injury, and often a dis- 

 tressing stricture of the chest, with a continued sense of pressure and 

 suffocation. 



(g.) Action on combustibles. A candle burns in this vapor with 

 some brilliancy, and phosphorus burns with splendor ignited charcoal 

 continues to burn, but with a dull red light. 



(h.) By calculation from the weight of the elements and their con- 

 densation, this acid, in the aerial form, must iveigh 65.3 grains, at 

 a medium temperature and pressure.' 



(*".) Action on colors. It is scarcely necessary to add that this 

 acid reddens litmus and affects the other test colors, as the acids gen- 

 erally do. 



(j.) The nitrous acid cannot be combined directly with the bases; 

 it affords with potassa, for instance, nitrate and hypo-nitrite, without 

 any proper nitrite. f 



3. Test for nitrous acid. We owe to Gay-Lussac the know- 

 ledge of the fact that the red sulphate of manganese becomes instantly 

 colorless by the action of the nitrous acids ; which, by detaching oxy- 

 gen, bring it to the state of w r hite sulphate, while nitric acid has no 

 such effect. 



4. REPRESENTATIVE NUMBER AND CONSTITUTION. As nitrous 

 acid is formed from 2 volumes of nitric oxide, consisting of equal 

 volumes of oxygen and nitrogen, with the addition of one volume of 



* For an ingenious theoretical explanation, more in detail, see Turner's Elements, 

 2d Ed. p. 225. 



t Ann. de Chim. et de Phya. T. I, p. 410. 



