Testing for hydrogen gas involves heating hydrogen gas over a flame and listening for a distinctive pop. Because hydrogen is highly flammable, it will react to the heat.
Using a flame is the best method of testing for the presence of hydrogen. Hydrogen has no color or smell and does not react to litmus paper because it is neutral. When using the flame test, hydrogen comes into contact with oxygen, creating hydrogen oxide. This process is called oxidation.
Hydrogen gas can be collected by heating water and placing a test tube over the surface to collect the gas. Because hydrogen is less dense than air and not soluble in water, it will displace the air within the tube. The test tube can then be clamped and heated over a flame.