HYDROGEN. 
21 
next most important element in nature. It is de- 
rived from two Greek words, signifying ^'water*^ 
and " to /orm," because with oxygen it forms water ; 
and, when exhibited, it is generally obtained from 
the decomposition of water. It is without taste or 
odour, and is the most inflammable of all substances. 
When mixed with atmospheric air, it burns with a 
violent explosion. Hydrogen is 14 times lighter 
than atmospheric air, and for this reason it is used 
to inflate balloons. It is obtained for this purpose 
by mixing together sulphuric acid, iron fihngs, and 
water, which results in the decomposition of the 
latter, and the consequent liberation of the hydro- 
gen. 
In order to form a correct idea of the quantity of 
hydrogen on the globe, we must bear in mind that 
water consists of two volumes of hydrogen and one 
of oxygen, and, consequently, so far as water is 
concerned, the quantity of hydrogen is double that 
of oxygen. With respect to the waters of the 
ocean, we must deduct about four per cent, for the 
amount of salts in solution; but with this allow- 
ance, when we reflect that the ocean has an aver- 
age depth of three miles, and covers three fifths of 
the surface of the globe, we perceive that there must 
be a vast amount of hydrogen locked up. To this 
must be added the immense quantity of water con- 
tained in rocks* and in the interior of the earth, 
which, though chiefly derived from the atmosphere 
in the form of rain, and filtering through immense 
* The following is a statement of the average per centum of 
water, in all the simple minerals containing it, that usually 
enter into the composition of rocks : 
Sulphate of lime .... 19.88 
Serpentine . 
Diallage . 
Talc and stealite 
Pyroxene 
Mica . 
Quartz . 
12.75 
8.20 
4.20 
3.74 
2.65 
1.62 
