AGRICULTURAL CHEMISTRY 



be liquefied; with greater difficulty, however, than any 

 other element. Hydrogen is 14.43 times lighter than air. 

 A liter of hydrogen, under standard conditions of tempera- 

 ture and pressure, weighs 0.08961 gram. Chemically, 

 hydrogen is characterized as combustible, but not a sup- 

 porter of combustion. It readily combines 

 with many other elements, particularly oxy- 

 gen, with which it forms water. When 

 hydrogen and oxygen unite to form water, 

 /^ a reaction takes place which causes a 



v contraction in volume. 



\i Two volumes of hy- 



drogen and one vol- 

 ume of oxygen unite 

 to produce two vol- 

 umes of water-vapor or 

 steam. When hydro- 

 gen and oxygen unite, 

 there is always an ex- 

 plosion, due to contrac- 



Fig. 19. Preparation of hydrogen, using a tion in Volume. That 

 wide-mouthed bottle and sink in place of 

 a Woulff bottle and pneumatic trough, water IS produced when 



hydrogen is burned, can be demonstrated by placing a dry 

 test-tube over a flame of hydrogen. The interior of the 

 test-tube will become covered with moisture. Hydrogen 

 does not unite with all elements as readily as does oxygen. 

 When hydrogen is burned, the flame is nearly colorless be- 

 cause the combustion is complete, and there are in the 

 flame no solid particles heated to incandescence. Hydro- 

 gen produces an exceedingly hot flame, and, when mixed 



