Acetylene is a gas. It burns with a very bright, very hot flame, and that is why people use it to cut metal and to join pieces of metal together. The usual tool is a torch that mixes acetylene with oxygen; the flame can cut steel. Years ago, before electric light was everywhere, acetylene was also burned in lamps because the light is so white and strong — old miners’ lamps worked that way. Though actually, the gas in a workshop cylinder is often dissolved in liquid acetone to keep it stable: the two words travel together in industry, but they are not the same substance. Acetylene is the gas; acetone is a liquid. Impure acetylene can smell a little like garlic. It is a specialist word: you hear it in workshops and in chemistry, not at the dinner table.