I have previously bemoaned the fact that MAPP gas is no longer available
- the Canadian factory/refinery which produced it partially shut down - but I'm in B+Q because I need some M10 studding in a hurry and Lo! and Behold!, and they have something called MAPGas in 400g disposable cylinders.
Now there are several so-called "substitutes" for MAPP gas, including one made Rothenberger called MAPGAS (note the different capitalisations) so I wasn't hopeful.
Mostly these substitutes are simply proylene aka propene, which isn't nearly as good as MAPP gas, you can't weld steel with it; MAPP was Methyl Acetylene/Propadiene mix stabilised with Propane (and sometimes Propene).
This is made by GoSystems however, and on the label it says: methylacetylene and propadiene mixture, stabilised - I buy one.
Get it home, and burn a bit without oxygen - black floaters!
Haven't tried an oxy-mix yet, as I haven't got the correct fitting for the top of the can, but I am one excited bunny :)
-- Peter Fairbrother
(this is only important for small-scale welders, but it means you can gas-weld steel without acetylene - MAPP isn't quite as good as acetylene for this, eg it can cause hydrogen embrittlement and you may have to heat-soak the finished article - though in practice for the small welder this is not a concern - but MAPP works, it's hot and energetic enough to weld steel, unlike the so-called "substitutes")