They are also in hydraulic systems and in some paints, inks and carbonless copy paper. Modern electrical equipment does not contain PCBs, but they are sometimes present in the condensers of old fluorescent light fittings, and old ceiling fans. PCBs can also be formed by the biological processes in rubbish dumps and traces of them are liable to be found in water leaching from the dumps. These are synthetic substances which are important industrially and environmentally. The best-known CFCs are gases, while others CFCs are volatile liquids.
Halons incorporate bromine instead of chlorine.
They are widely used in fire-extinguishing installations in aircraft, and in computers. It is also widely used as a solvent in the form of methylated spirits. Ethanol is often added to petrol. Methyl alcohol, or wood spirit, originally was made from wood but is now produced from natural gas. It is an important raw material and solvent in the chemical industry.