80 WATER 



and other bubbles of gas rising from the end of the wire by 

 which the -current leaves the water. These gases have evi- 

 dently come from the water and are the substances of which 

 it is composed, because the water begins to disappear as the 

 gases are formed. If we place over each end of the wire an 

 inverted jar filled with water, the gases are easily collected. 

 The first thing we notice is that there is always twice as much 

 of one gas as of the other ; that is, water is composed of two 

 substances, one of which is always present in twice as large 

 quantities as the other. 



73. The Composition of Water. On testing the gases into 

 which water is broken up by an electric current, we find them 

 to be quite different. One proves to be oxygen, a substance 

 with which we are already familiar. The other gas, hydro- 

 gen, is new to us and is interesting as being the lightest 

 known substance, being even "lighter than a feather." 



An important fact about hydrogen is that in burning it 

 gives as much heat as five times its weight of coal. Its flame 

 is blue and almost invisible by daylight, but intensely hot. 

 If fine platinum wire is placed in an ordinary gas flame, it 

 does not melt, but if placed in a flame of burning hydrogen, it 

 melts very quickly. 



74. How to prepare Hydrogen. There are many different 

 methods of preparing hydrogen, but the easiest laboratory 

 method is to pour sulphuric acid, or hydrochloric acid, on zinc 

 shavings and to collect in a bottle the gas which is given off. 

 This gas proves to be colorless, tasteless, and odorless. (See 

 Laboratory Manual.) 



