118 Introduction to the Study of Science 



is water formed? " he answered thus : " water is formed by the 

 union in combustion of oxygen and ' inflammable air.' " 



This name for the substance is not convenient and falls short 

 also of indicating its role in water and in other compounds. 

 Because it is one of the chief constituents of water, and because 

 when burned in oxygen either pure or as present in the air, 

 it produces only water, it was named by Lavoisier " water- 

 former " or hydrogen. 



We learn from our study that at least one of the products of 

 the candle burning in air is water. The analysis of water by 

 the electric current makes it certain that water is composed of 

 at least two substances, oxygen and hydrogen. Thus the 

 circle seems to be complete. Hydrogen, when burned either 

 in pure oxygen or in the oxygen contained in the air, produces 

 water, and water is decomposed by a certain amount of elec- 

 tricity, which is the equivalent of a certain amount of heat, 

 into hydrogen and oxygen. 



The production of hydrogen. Water is clearly one of the 

 products of the burning candle. The technical name of 

 water is hydrogen oxid, showing that it is a compound of 

 hydrogen and oxygen. Before we seek the source of hydro- 

 gen in the burning candle, we may advantageously study 

 more fully the nature, behavior, and principal compounds of 

 hydrogen. 



From water. Hydrogen is abundant in water, existing in 

 the ratio of two volumes to one of oxygen. It can be liberated 

 from water by electrolysis, as you have learned ; but it may 

 be set free more rapidly by certain metals, such as magnesium, 

 calcium, sodium, iron, and zinc. Iron and zinc require high 

 temperatures. Magnesium acts, as you have observed, in 

 steam, separating oxygen and hydrogen and liberating the 

 latter. Sodium reacts too violently for safety. Calcium 

 liberates hydrogen in a safe but also rapid manner. A quantity 

 of hydrogen may be obtained by holding a bottle filled with 

 water over a small lump of the metal calcium placed in a vessel 



