6. Gas mixtures

The industry produces and uses a large number of gas mixtures that can be considered as service fluids:

• welding mixture often based on argon and carbon dioxide sold under various trade names: for example, Atal or Cargal (Air Liquide);

• mixing a neutral gas with a highly combustible gas to make safe use of certain properties of the latter: e.g. ethylene-nitrogen mixture;

• synthetic air made by mixing oxygen and nitrogen (widely used in hospitals to ensure totally clean air).

Generally speaking, gas producers can manufacture any mixture useful in an industry, provided it can be produced and stored without any particular danger. A detailed study of these mixtures is out of the question here. We shall confine ourselves to a few useful general...