172 N OX-METALS AND THEIR COMBINATIONS. 



Such a decomposition which proceeds at high temperatures, while at lower ones 

 the constituents can recombine, is called dissociation. 



When electric sparks pass through atmospheric air some ozone is generated 

 which oxidizes nitrogen, forming first the lower and then also the higher 

 oxides; these combine with water to form nitrous and nitric acid, which acids 

 are taken up by the ammonia present in the air, forming the respective 

 ammonium salts. 



Nitrogen monoxide, N 2 O (sometimes called nitrous oxide ; 

 also laughing gas). This compound was discovered by Priestley in 

 1776; its anaesthetic properties were first noticed in 1800 by Sir 

 Humphry Davy, and it was first used in dentistry by Dr. Horace 

 Wells, a dentist of Hartford, Conn., in 1844. It may be easily 

 obtained by heating ammonium nitrate in a flask at a temperature 

 not exceeding 250 C. (482 F.), when the salt is decomposed into 

 nitrogen monoxide and water : 



NH<NO 3 = 2H,O + N 3 O. 



When nitrous oxide is prepared for use as an anesthetic it should 

 be passed through two wash-bottles containing caustic soda and ferrous 

 sulphate respectively ; these agents will retain any impurities that may 

 be formed during the decomposition, especially from an impure salt 



Ammonium nitrate to be used for generating pure nitrous oxide should be 

 completely volatilized when heated on platinum foil ; its solution in water 

 should not be rendered turbid by silver nitrate, as this would indicate the 

 presence of chlorides. These latter are objectionable because gaseous com- 

 pounds of chlorine with the oxides of nitrogen may be formed. If the gas is 

 prepared as directed above, it can be used with safety. 



Impurities found in the gas when not properly made are air, nitric oxide, 

 chlorine, chloronitrous and chloronitric oxides. 



If the gas is stored over water, considerable loss is experienced on account 

 of the solubility of nitrous oxide in cold water. This loss can be diminished 

 by using hot water or a concentrated solution of common salt in water, both of 

 which liquids dissolve less of the gas. 



Experiment 8. Use apparatus as represented in Fig. 37, page 140. Place in the 

 dry flask about 10 grammes of ammonium nitrate, apply heat, collect the gas 

 in cylinders over water, and verify by experiments and observations the correct- 

 ness of the statements below regarding the physical and chemical properties 

 of nitrogen monoxide. 



Nitrogen monoxide is a colorless, almost inodorous gas, of dis- 

 tinctly sweet taste. It supports combustion almost as energetically 

 as oxygen, but differs from this element by its solubility in cold water, 

 which absorbs nearly its own volume. Under a pressure of about 

 50 atmospheres it condenses to a colorless liquid, the boiling-point of 

 which is at about -90 C. (-130 F.) and the freezing-point at 

 -102 C. (-151.6 F.). 



