148 FIRST YEAR COURSE IN GENERAL SCIENCE 



furnish it pure to patients to breathe in some cases of 

 extreme weakness, thus prolonging life a short time. 



159. Hydrogen. There are two other gaseous elements, 

 hydrogen and nitrogen, that are common enough to be of 

 great interest. They are not very well known because un- 

 der ordinary conditions they are, like oxygen, invisible. 

 Hydrogen, the lightest substance known, is only about one 

 fourteenth as heavy as air. It is not often found in nature 



FIG. 76. BURNING HYDROGEN 



FIG. 77. ELECTROLYSIS OF WATER 



FIG. 76. 1. What is the product of hydrogen burning openly in air? 

 2. Could the substance be seen? 3. What would be the effect of placing 

 a cool jar over the flame? Explain. 



FIG. 77. The two arms of the U-shaped tube were full of water when the 

 current began to pass between the pieces of platinum near the bend. 1. 

 Compare the condition of the two arms now. 2. What is the meaning of 



in the gaseous form, as oxygen is, uncombined with other 

 elements; but it makes one ninth of the weight of water 

 and is found in many other compounds. Hydrogen is com- 

 bustible, that is, it will burn. When burned in pure oxygen, 

 it makes one of the hottest flames known the oxyhydro- 

 gen flame, which is used to melt metals and minerals that do 

 not melt in ordinary fires. It is also used to heat white-hot 

 the block of lime which gives the intense light used in many 



