88 NON-METALS AND THEIR COMBINATIONS. 



The gaseous compounds N 2 O 2 and N 2 O 4 exist as such at low temperatures 

 only, and readily split up at a high temperature into the compounds NO and NO 2 . 

 This splitting up of molecules is known as dissociation. The terms nitrogen 

 dioxide and nitrogen tetroxide should be applied only to the compounds N 2 O 2 

 and N 2 O 4 , but they are used also for the products of dissociation NO and NO 2 . 



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=44. (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 

 Humphrey Davy, and it was first used in dentistry by Dr. Howard 

 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 4 NO 3 = 2H 2 O + N 2 0. 



When nitrous oxide is prepared for use as an anaesthetic 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. 



Experiment 6. Use apparatus as represented in Fig. 6, page 75. 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 80 C. ( 112 F.) and the freezing-point at 

 _100 C. (148 F.) 



When inhaled it causes exhilaration, intoxication, anaesthesia, and 

 finally asphyxia. The gas is used in dentistry as an anaesthetic, the 

 liquefied compound being sold for this purpose in wrought-iron 

 cylinders. 



Nitrogen dioxide, NO=3O. This is a colorless gas which is 

 formed generally when nitric acid acts upon metals or upon sub- 



