Fire and Heat 



119 



of water. The ascending gas displaces the water and occupies 

 the space in the bottle. 



Another way of getting hydrogen, and one which shows at 

 the same time the wonderful attraction of metals for oxygen, 

 is to pass steam over red-hot iron fragments. The steam is 

 broken down, the oxygen uniting with the hot iron, and the 

 hydrogen passes off. A similar reaction occurs in passing steam 

 through white-hot coal or carbon in the manufacture of " water 

 gas" (page 162). Water gas burns with a flame like that of 

 hydrogen, or is almost non-luminous. 



From acids. A very common laboratory method of obtaining 

 hydrogen with the apparatus shown in Fig. 37 is the following. Put 

 a small quantity of granulated or moss zinc into the flask and supply 

 through the funnel tube small 

 amounts of dilute sulfuric 

 acid. The generated gas is 

 conducted through water and 

 is collected in bottles over 

 water. If air is mixed with 

 the gas, a more or less danger- 

 ous explosion is certain. Stu- 

 dents should exercise care, and 

 the instructor should super- 

 vise the experiment closely. 



FIG. 37. Apparatus for making and col- 



When the hydrogen is coming lectin s hydrogen. The hydrogen of the sul- 

 freely from the end of the ^ acid W* sulfate > is re P laced ^ 

 rubber tubing, collect four or 



more bottles of the gas. Slip a piece of glass under the mouth of each 

 bottle as it is filled ; lift the bottle vertically and set it away in an 

 inverted position. 



The reason for using zinc and sulfuric acid in generating 

 hydrogen is that zinc, or any other of a whole series of metals, 

 enters into an interesting combination or exchange with sul- 

 furic or certain other acids. Zinc is a simple substance, or an 

 element. Sulfuric acid is a compound produced from sulfur, 

 oxygen, and hydrogen. When the acid is brought into contact 

 with zinc, it begins at once to exchange hydrogen for the zinc, 



