290 PRINCIPLES OF CHEMISTRY 



Nitrous oxide forms a very mobile, colourless liquid, which acts on the 

 skin, and which is incapable in a cold state of oxidising either 

 metallic potassium, phosphorus, or carbon ; its specific gravity is 

 slightly less than that of water (O94). When evaporated under the 

 receiver of an air-pump, the temperature falls to 100, and the 

 liquid solidifies into a snow-like mass, and partially forms transparent 

 crystals. Both these substances are solid nitrous oxide. Mercury 

 is immediately solidified in contact with evaporating liquid nitrous 

 oxide. 73 



When introduced into the respiratory organs (and consequently 

 into the blood also) nitrous oxide produces a peculiar kind of drunken- 

 ness accompanied by spasmodic movements, and hence this gas, dis- 

 covered by Priestley in 1776, received the name of * laughing gas.' On a 

 prolonged respiration it produces a state of insensibility (it is an 

 anaesthetic like chloroform), and it is therefore employed in dental and 

 surgical operations. 



Nitrous oxide is easily decomposed into nitrogen and oxygen by the 

 action of heat, or a series of electric sparks ; and this explains why a 

 number of substances which cannot burn in nitric oxide do so with 

 great ease in nitrous oxide. In fact, when nitric oxide gives some 

 oxygen on decomposition, this oxygen immediately unites with a fresh 

 portion of the gas to form nitric peroxide, whilst nitrous oxide does 

 not possess this capacity for further combination with oxygen. 74 A 

 mixture of nitrous oxide with hydrogen explodes like detonating 

 gas, gaseous nitrogen being formed, N 2 O + H 2 =H 2 O + N 2 . The 

 volume of the remaining nitrogen is equal to the original volume of 

 nitrous oxide, and is equal to the volume of hydrogen entering into 



pressure of 25mm. carbonic anhydride gives a temperature as low as 115, and nitrous 

 oxide of 125 (Dewar). The similarity of these properties and even of the absolute 

 boiling point (CO 2 + 32, N 2 O + 86) is all the more remarkable because these gases have 

 the same molecular weight = 44 (Chap. IV. Note 10, and Chap. VII.). 



73 A very characteristic experiment of simultaneous combustion and of intense. 

 cold maybe conducted by means of liquid nitrous oxide; if liquid nitrons oxide be 

 poured into a test tube containing some mercury, then the mercury will solidify, and if 

 a piece of red-hot charcoal be thrown upon the surface of the nitrous oxide it will con- 

 tinue to burn very brilliantly, giving rise to a high temperature. 



74 In the following chapter we shall consider the volumetric composition of the 

 oxides of nitrogen. It explains the difference between nitric and nitrous oxide. 

 Nitrous oxide is formed with a diminution of volumes (contraction), nitric oxide without 

 contraction, its volume being equal to the sum of the volumes of nitrogen and oxygen of 

 which it is composed. By oxidation, if it could be directly accomplished, two volumes of 

 nitrous oxide and one volume of oxygen would not give three but four volumes of nitric 

 oxide. These facts must be taken into consideration in comparing the calorific equiva- 

 lents of formation, the capacity for supporting combustion, and other properties of nitrous 

 and nitric oxides, N 2 O and NO. 



