BURNING OF HYDROGEN 



99 



soap 



soluble in water (cf. 100), and is collected "over water," just as 

 oxygen and nitrogen are. 



104. Properties of Hydrogen. Like oxygen and nitro- 

 gen, hydrogen has no odor, taste, or color. It is the light- 

 est substance known. Oxygen is 16 times as heavy as 

 hydrogen, and nitrogen is 14 



times as heavy. At the ordinary 



temperature and pressure 1 gram 



of hydrogen has a volume of 



about 12 liters, i. e., about 3 gal- 



lons (cf. Appendix, Table IV). 



Because of its lightness, hydrogen 



may be collected "over air" (Fig. 



79, J5), and may be used to fill 



balloons. Soap bubbles filled with the gas rise in air 



(Fig. 80). 



105. Burning of Hydrogen. If we wish to burn hydro- 

 gen in a jet (Fig. 81), we must light it with great care. 



When we begin the prep- 

 aration of hydrogen, the 

 bottle is full of air; hence 

 the first portions of gas 

 that come off are a mix- 

 ture of hydrogen and air. 

 If we light this mixture, 

 there will be a violent ex- 

 plosion, which may break 

 the bottle, and blow the 



FIG. 81. . . 



Hydrogen burns in air to form water. glaSS mtO OUr laCeS. 



