NITROGEN. 173 



When inhaled it causes exhilaration, intoxication, anaesthesia, and, 

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

 liquefied compound being sold for this purpose in wrought-iron 

 cylinders. There are two sizes of these cylinders : the smaller con- 

 tain about one and a half pounds of the liquid, equal to 100 gallons 

 of gas; the larger size contains about five times that quantity. 



Nitric oxide, NO. This is a colorless gas which is formed gener- 

 ally when nitric acid acts upon metals or upon substances which 

 deoxidize it. It is capable of combining directly with one or more 

 atoms of oxygen, thereby forming nitrogen tetroxide, called nitrogen 

 peroxide, NO 2 or N 2 O 4 , which is a gas of deep red color and poison- 

 ous properties. Nitrogen trioxide, N 2 O 3 , exists as an indigo-blue 

 liquid at temperatures below 21 C. (-6 F.); above this tem- 

 perature it decomposes into NO and NO 2 . 



Experiment 9. Use apparatus as shown in Fig. 38. Put about 20 grammes 

 of copper or brass turnings into the flask and pour through the funnel tube a 

 mixture of 30 c.c. concentrated nitric acid and 50 c.c. water. Apply gentle 

 heat and collect several bottles of gas. ^Note that the gas. in the flask is at 

 first colored. Why? Remove the cover from a bottle of the gas, and explain 

 the result. Insert a stick with a flame into another bottle of the gas, and com- 

 pare with the action of nitrous oxide. If copper is used, filter the solution 

 after all copper is dissolved, and evaporate to get blue crystals of copper 

 nitrate. For explanation of the reaction, see below, under Nitric Acid. 



Hyponitrous acid, HNO, or possibly H 2 N 2 2 , is a very unstable white, 

 flaky solid. Neither the acid, nor its salts, the hyponitrifces, are of practical 

 interest. 



Nitrous acid, HNO 2 , has not been obtained in a pure state, but 

 exists in solution. Several of its salts, the nitrites, are well known 

 and are used analytically and otherwise. Nitrous acid very readily 

 breaks down into water and its anhydride, N 2 O 3 , which escapes as 

 brown fumes from the solution. Hence, the salts of the acid are 

 decomposed by nearly all other acids. Nitrous acid acts as an oxid- 

 izing agent toward some substances, being itself reduced to lower 

 oxides, and as a reducing agent toward others, being then oxidized to 

 nitric acid. A solution of nitrous acid in water or other acids has a 

 pale blue color. 



Tests for nitrous acid and nitrites. 

 (Use about a 5 per cent, solution of sodium or potassium nitrite.) 

 1. To 5 c.c. of the solution, add a little strong sulphuric acid. Note 

 the colored fumes and effervescence and the bluish color of the liquid. 



