Stink-damp or sulphuretted hydrogen is chemically known as hydrogen sulphide. It is produced in mines by the decomposition of sulphides of iron (pyrites) which are often present in coal and adjacent strata. The gas is colourless, but has a disagreeable taste and a strong pungent odour very much like that of rotten eggs. It is very flammable, but does not support combustion. It is very explosive when mixed with air in certain proportions and ignited.