56 



SMITH'S INTERMEDIATE CHEMISTRY 



Chemical Properties of Hydrogen. That hydrogen, when 

 it burns in the air, forms water, was first shown by Cavendish 

 (1781). A test-tube or beaker, filled with cold water and held 

 over a flame of burning hydrogen, will condense the steam to 

 droplets of water (Fig. 28). 



Hydrogen -f- Oxygen > Water. 



The union is very violent, so that when a mixture of hydrogen 

 with pure oxygen is set on fire (they do not unite when cold) 

 much heat is liberated in the explosion. The gases can be made 



J 



FIG. 28 



FIG. 29 



to burn quietly, but with an exceedingly hot flame, by the use of 

 an oxy-hydrogen burner (Fig. 29), which is constructed like a blast 

 lamp. Iron melts and burns in the flame. A piece of 

 quicklime, held in the flame, glows with a brilLant 

 white light the calcium light (Drummond light or 

 lime-light). For such uses the gases are obtained in 

 compressed form in iron cylinders (Fig. 30). 



Hydrogen combines vigorously with chlorine, giving 

 hydrogen chloride, a gas of which hydrochloric acid is 

 a solution. It unites with the three most active 

 metals in the list (p. 54). Calcium hydride is sold 

 under the name of hydrolyte, and is used, on ac- 

 count of its action on water, as a source of hydro- 

 gen. 



Hydrogen acts upon many compounds containing 

 oxygen, removing the latter to form water. Thus when the 



FIG. 30 



