Mapp® gas is liquefied petroleum gas (LPG) mixed with methylacetylene-propadiene. Mapp® is the tradename for a product
of the Dow Chemical Company.
The gas is used for welding due to its high combustion
temperature of 2927 °C (5301 °F) in oxygen. Although acetylene
has a higher welding temperature (3160 °C, 5720 °F), Mapp® has
the advantage that it requires neither dilution nor special
container fillers during transport, allowing a greater volume of
welding gas to be transported at the same given weight. Also, Mapp® is advantageously used in underwater welding, which
requires high gas pressures (under such pressures acetylene
transforms explosively to benzene, making it dangerous to use).
The gas is also used for brazing and soldering, under combustion
in ambient air, where it has considerable advantage over
competing propane fuel due to its higher combustion temperature.
A typical Mapp® gas brazing operation would involve using it to
silver braze (sometimes colloquially and inaccurately called
silver solder) steel parts together.
Plumbers use both Mapp® gas and propane for pipe soldering and
brazing, but Mapp® gas's higher combustion temperature makes
such jobs quicker. Mapp® gas is also popular among glass lampworkers, for instance glass bead makers.
The biggest disadvantage of Mapp® gas is cost; it is between two
and four times as expensive as propane.
Mapp® is colorless in both liquid and gas form. The gas has a
pronounced garlic or fishy odor at concentrations above 100 ppm
and is toxic if inhaled at high concentrations.
