The latter include cracking gas, acetylene, ethylene, propylene and butadiene. Soot forms during incomplete combustion from precursor molecules such as acetylene. Propane is cheaper than acetylene and easier to transport. It can be seen as a lattice of benzene rings connected by acetylene bonds. The butanediol is derived from condensation of acetylene with formaldehyde followed by hydrogenation. The outer jets are for preheat flames of oxygen and acetylene. Alcohols and phenols add to acetylene to give vinyl ethers. Polyacetylene can also be produced by radiation polymerization of acetylene. Adjustment is made by adding more or less oxygen to the acetylene flame. It arises from the condensation of acetylene and acetone. They include ethane , acetylene , methylacetylene , diacetylene . LPG will damage an incompatible hose, including most acetylene hoses. Acetylene usage for welding has dropped significantly. This interval can be very small (kerosene) or large (acetylene). Internally graphitized tubes via acetylene thermal decomposition are passivated.