11.   The gases are odourless.

12.   Most gases are covalent compounds, although, of course, the noble gases are exceptions.

13.   All gases are miscible and thus they can all diffuse through each other.

14.   The gas is collected and can be burned directly for domestic heating and cooking or used to produce electricity in a generator.

15.   This means that, in a well organised theatre, with professional embalmers, very little formaldehyde gas is likely to be released into the atmosphere.

16.   None the less, gas is crucial in the actual mechanisms which control the kind of eruptive activity that occurs.

17.   But at the rate emissions of CFCs are growing, the gases are likely to overtake carbon dioxide as principal contributors to the global warming problem.

18.   On the day of the explosion winds were calm and the gas was slow to dissipate.

19.   At present, gas is up to one-third cheaper to generate.

20.   The naturally-occurring invisible gas is present to some extent in every home in Britain.