84 NON-METALS AND THEIR COMBINATIONS. 



3. Solution of potassium permanganate, acidified with sulphuric 

 acid, is readily decolorized with evolution of oxygen : 



5H 2 O 2 + 2KMnO 4 + 3H 2 SO 4 = 8H 2 O + 2MnSO 4 -f K 2 SO 4 + 10 O. 



This reaction is made use of in the volumetric analysis of hydrogen 

 dioxide. (See Chapter 37.) 



12. NITROGEN. 



Nili = 14 (14.01). 



Occurrence in nature. By far the larger quantity of nitrogen is 

 found in the atmosphere in a free state. Compounds containing 

 nitrogen are chiefly the nitrates, ammonia, and many organic sub- 

 stances. 



Preparation. Nitrogen is obtained usually from atmospheric air 

 by the removal of its oxygen. This may be accomplished by burn- 

 ing a piece of phosphorus in a confined portion of air, when phos- 

 phoric oxide, a white solid substance, is formed, whilst nitrogen is left 

 in an almost pure state. 



Other methods for obtaining nitrogen are by heating a mixture of 

 potassium nitrite and ammonium chloride dissolved in water : 



KNO 2 + NH 4 C1 = KC1 + 2H 2 O + 2N; 

 Potassium Ammonium 

 nitrite. chloride. 



or by heating ammonium nitrite in a glass retort : 

 NH 4 NO 2 = 2H 2 + 2K 



Experiment 4. Use an apparatus as shown in Fig. 6, page 75. Place in the 

 flask about 10 grammes of potassium nitrite and nearly the same amount of 

 ammonium chloride ; add enough water to dissolve the salts, and apply heat, 

 which is to be carefully regulated from the time the decomposition begins, as 

 the evolution of gas may otherwise become too rapid. Collect the gas, and 

 notice its properties mentioned below. 



QUESTIONS. 101. Mention two processes by which hydrogen may be ob- 

 tained. 102. Show by symbols the decomposition of water by potassium, and 

 of sulphuric acid by iron. 103. State the chemical and physical properties of 

 hydrogen. 104. How many pounds of zinc are required to liberate 100 pounds 

 of hydrogen ? 105. State the composition of water in parts by weight and by 

 volume. 106. Mention the most common solid and gaseous constituents of 

 natural waters. 107. How does a mineral water differ from other waters? 

 Mention some different kinds of mineral waters and their chief constituents. 

 108. What are the characteristics of a good drinking-water? 109. What are 

 the purest natural waters, and by what process may chemically pure water be 

 obtained? 110. State composition, mode of manufacture, and properties of 

 hydrogen dioxide. 



