5.15 Cool Fire

Chemical Concepts Demonstrated: Ignition point, combustion temperature, flash point

Demonstrations (three possible):

  1. A piece of paper soaked in CH3OH (methanol) / H2O solvent mixture is ignited.
  2. A $1.00 bill is soaked in 190-proof ethanol/H2O solvent mixture and ignited.   To add some showmanship, borrow the money from someone in the class.
  3. The CCl4/CS2 mixture is poured onto a piece of cloth and ignited.

Observations:

   In all of the cases stated above, the solution used is burned up while the thing the solution is on remains unaffected.

Explanation:

    The solutions burn at lower temperatures than the paper or cloth involved.  When a flame is applied, the solution (which is easier to ignite) burns before the fire moves onto the paper or cloth (which is harder to ignite).  Because it requires less energy for the fire to continue to burn the "fuel" solutions than to attempt to ignite the paper, the items soaked in the solutions remain unharmed.