This oxy-acetylene flame is used for welding metals, where very high temperatures are required. Alkynes are more reactive than the alkanes or alkenes due to the presence of unsaturated bonds. The pi bond is not localized and hence can be broken easily in a reaction. Such a reaction is called addition reaction. In an addition reaction, the pi bond converts into a sigma bond and the alkyne will become an alkane.
Bromine water decolorizes on reaction with ethyne.
This is a prominent test for testing unsaturated nature of hydrocarbons. When hydrogen is added to ethyne, and heated in the presence of nickel, it becomes ethene and then proceeds to become ethane. The bonds become saturated. This is known as the process of hydrogenation. The addition of hydrogen to a double or triple bonded hydrocarbon leads to saturation of the bonds.