REDUCTION OF NITROUS ACID. 53 



between ammonia and nitrous acid, as I hope to render experi- 

 mentally evident to you. 



(53.) Thus, on passing a series of electric sparks from the 

 Kiihmkorff machine through the moist air contained in this 

 apparently empty glass cylinder, a portion of the nitrogen of the 

 contained air becomes gradually oxidised, and after a short time 

 we shall see brown nitrous fumes make their appearance, in 

 accordance with this reaction : 



Nitrogen Oxygen Water Nitrous acid 



N 3 + 3 + H a O = 2HNO a 



By allowing the experiment to continue, the depth of colour 

 in the cylinder will go on increasing so as to be visible from every 

 part of the theatre. But I dare say I shall be able to render the 

 nitrous acid already produced abundantly manifest, by allowing it 

 to act upon a piece of paper stencilled with starch and iodide of 

 potassium solution. That we have really obtained a consider- 

 able amount of nitrous acid, by the few sparks which have as yet 

 passed through the air in the cylinder, is shown by the speedy 

 liberation of iodine from the iodide of potassium, and consequent 

 appearance of the word NITROUS in purple characters upon the 

 prepared paper. 



(54.) Now for the reverse experiment. In this flask is a mix- 

 ture of materials for generating hydrogen, namely, a little granu- 

 lated zinc, some iron borings, and warm solution of potash. 

 Active effervescence quickly takes place, aud the evolved gas, 

 which is without action on turmeric paper, as you perceive, 

 bums with the characteristic flame of hydrogen. If we now 

 absorb the brown nitrous fumes contained in this gas-bottle, 

 by agitation with aqueous potash, and pour the solution so 

 produced of nitrite and nitrate of potassium into our hydrogen 

 flask, you observe that the effervescence becomes more rapid, 

 and that the evolved gas is now decidedly ammoniacal, as shown 

 by its browning the turmeric paper and fuming with the hydro- 

 chloric acid vapour I bring into its neighbourhood. The re- 

 action taking place in the flask is represented in this equation, 



