NITROGEN. 73 



gravity 1.45, possessing remarkable bleaching properties. By 

 higher temperatures, as well as by the action of many sub- 

 stances, it is readily decomposed into water and oxygen. 



QUESTIONS. 



101. Mention two processes by which hydrogen may be obtained. 



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

 sulphuric acid by iron. 



103. State the chemical and physical properties of hydrogen. 



104. How many pounds of zinc would be required to liberate 100 

 pounds of hydrogen ? 



105. State the composition of water in parts by weight and 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 substances are most objectionable in drinking water, and 

 how can they be recognized? 



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



110. What are the purest natural waters, and by what process may 

 chemically pure water be obtained ? 



12. NITROGEK 



N iji = 14. 



Occurrence in nature. By far the larger quantity of nitrogen 

 is found in the atmosphere in a free state. Compounds con- 

 taining nitrogen are chiefly the nitrates, ammonia, and many 

 organic substances. 



Preparation. Nitrogen is usually obtained from atmospheric 

 air by the removal of oxygen. This may be accomplished by 

 burning a piece of phosphorus in a confined portion of air, 

 when phosphoric oxide, a white solid substance, is formed, 

 whilst nitrogen is left in an almost pure state. 



Properties. Nitrogen is a colorless, inodorous, tasteless gas. 

 It is neither, like oxygen, a supporter of combustion, nor, like 

 hydrogen, a combustible substance; in fact, nitrogen is dis- 

 tinguished by having very little affinity for any other element, 



