86 THE REASON WHY. 



"As smoke is driven away, so drive them away: as wax melteth before the fire, 

 so let the wicked perish at the presence of God." PSALH XLVI. 



or with the comimn air, which contains oxygen. * Two measures of 

 hydrogen and one of oxygen form a most explosive compound. 



53. Why does hydrogen explode, when mixed with oxygen, 

 upon being brought in contact with fire ? 



Because of its strong affinity for oxygen, with which, upon the 

 application of heat, it unites to form water. 



54. Wliere does hydrogen chiefly exist ? 



In the form of water, where it exists in combination with oxygen. 

 Eleven parts of hydrogen, and eighty-nine of oxygen, form water. 



55. Is hydrogen found elsewhere ? 



It is never found but in a state of combination ; united with 

 oxygen, it exists in water; with nitrogen, in ammonia; with 

 chlorine, in hydro-chloric acid; with fluorine, in hydro-fluoric acid; 

 and in numerous other combinations. 



56. Is the gas used to illuminate our streets, hydrogen gas? 

 It is ; but it is combined with carbon, derived from the coals from 



which it is made. It is therefore called carburetted hydrogen, 

 .which means hydrogen with carbon. 



57. How is hydrogen gas obtained from coals ? 



It is driven out of the coals by heat, in closed vessels, which pre- 

 vent its union with oxygen. 



58. Wliat becomes of the water wliich is formed by the 

 burning of hydrogen in oxygen ? 



It passes into the air in the form of watery vapour. Frequently 

 it condenses, and may be seen upon the walls and windows of rooms 

 where many lights or fires are burning. Sometimes, also, portions 

 of it become condensed in the globes of the glasses that are 

 suspended over the jets of gas. A large volume of these gases 

 forms only a very small volume of water. 



59. What becomes of the carbonic acid gas which is pro- 

 duced by combustion ? 



It is diffused in the air, which should be removed by adequate 

 ventilation, 



