Physical properties of hydrogen
Pure hydrogen is a colorless, odorless, tasteless gas. It is not poisonous, and may therefore be inhaled without harm. It is the lightest known substance, being about 14.4 times lighter than air, 16 times lighter than oxygen, and 11,000 times lighter than water.
Chemical properties of hydrogen
Hydrogen does not unite with oxygen at ordinary temperatures, but, like wood and most other fuel substances, needs to be heated up to the kindling temperature before it will burn. Hydrogen burns if a lighted match be applied to it. The flame is colorless, or very slightly blue.
Decomposition of water
Water—Water is a compound and not an element, as can be shown by passing an electric current through it. If the ends of two wires, each connected with an electric battery, be put a short distance apart, in acidulated water, it will be noticed that bubbles of gas rise from each wire. As these gases cannot come from, or through the wires, they must be formed from the water. If they be analyzed, we will find that oxygen gas comes from one wire and hydrogen from the other.
Proportion of hydrogen and oxygen in water
This experiment shows that when an electric current is passed through water, hydrogen and oxygen are obtained, and also that there is obtained twice as much hydrogen as oxygen by volume. This proves that water is not an element, but a compound of two atoms of hydrogen and one of oxygen. The chemist therefore writes the symbol for water H2O.
We have just learned that with electricity we could decompose the compound water into its elements, hydrogen and oxygen. Now we can prove by another experiment that water contains these two elements. If we burn hydrogen gas, or any substance containing hydrogen, water is formed. This can be illustrated by inverting a cool, dry tumbler over a gas flame, which is composed chiefly of hydrogen, and water vapor will collect on the inside.
Properties of water