THE CHEMISTRY OP WATEE. HYDROGEN. 123 



Fig. 47, at the same time into the bottle you expel the gas, 

 and thus keep up a brisk burning till the gas is all consumed. 

 In the common illuminating gas we have a mixture of olefi- 

 ant and marsh gas. The brightness of the flame is owing 

 to the greater quantity of carbon which is in the former, as 

 will be noticed more particularly 'in the next chapter. 



155. Hydrogen Peroxide, H 2 O 2 . Water was for a long time sup- 

 posed to be the only compound of oxygen and hydrogen. It is really the only 

 compound existing in nature ; but another can be produced by a chemical 

 process that has exactly twice as much oxygen in it as water. It is called 

 hydrogen peroxide, water being considered as an oxide. This substance 

 has very peculiar qualities, differing greatly from those of water. It is a sir- 

 upy, colorless, transparent liquid, having a slight odor, and a very nau- 

 seous and astringent taste. The quality in which it differs most from 

 water is that no degree of cold can freeze it. The contact of carbon will 

 decompose it instantly, often with an explosion and a flash of light. 

 Heat also decomposes it, producing an effervescence. This singular com- 

 pound seems to have no tendency to combine with any other substance, 

 and as yet has not been found to be of any value, but a mere chemical 

 curiosity. 



156. Nature of Hydrogen. It is a common supposition 

 among chemists that hydrogen is a metal having two ox- 

 ides, water and hydrogen peroxide. At first thought it 

 seems impossible that this is true of the lightest substance 

 in the world. Metals we are accustomed to think of as be- 

 ing heavy and solid. But, as you will see in a future chap- 

 ter, there are some metals sufficiently light to float on wa- 

 ter. Besides, we have one metal, mercury, that is a liquid, 

 and why should there not as well be a gaseous metal ? And, 

 farther, the metal mercury is in a state of invisible vapor in 

 the space over the metal in every thermometer and barome- 

 ter. If a metal, then, can thus be gaseous under certain 

 circumstances, what difficulty is there in conceiving one to 

 be so under all ordinary circumstances ? Moreover, a com- 

 pound of the very rare metal palladium with hydrogen has 



