In the cycle shown below there are three separate chemical reactions represented:

• Reaction 1 : Sulphur powder is heated strongly with iron filings in a test tube. After a while the contents of the tube will glow and iron II sulphide is formed.
   
• Reaction 2 : Once the iron II sulphide has cooled down dilute hydrochloric acid is added to it. This is done in a fume cupboard since one of the products, hydrogen sulphide gas, has a pungent odour similar to bad eggs. The hydrogen sulphide gas is collected in a gas jar.
   
• Reaction 3: Oxygen gas is mixed with the hydrogen sulphide gas. A lighted match will ignite these two gases. The products of this reaction are water and powdered sulphur.

The element sulphur is found in volcanic areas. It forms yellow deposits around the crater of a volcano.

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