When ethyne is burnt in oxygen,large quantity of heat alongwith light is produced. The heat eveolved can be used for gas welding which is usually carried to weld small broken pieces of articles made up of iron.
`C_(2)H_(2)(g)+5//2O_(2)(g)to2CO_(2)(g)+H_(2)O(l)+"Heat and light"`
Air mainly contains a mixture of nitrogen (4 parts) and oxygen (1 part). As we know, nitrogen gas does not support combustion. thismeans that in air, only oxygen will help in the combustion of ethyne. Therefore, it is always better to use oxygen for the combustion of ethyne.