Investigation of different parts of a flame

We can easily find out whether or not the inside of a flame is cool. Two experiments can prove this:

1. (a) When a piece of cardboard is held horizontally over a non-luminous flame, we notice a burn mark as shown below:

When held vertically over the flame, the burn mark is as shown in above. Note that when performing this experiment, the cardboard should be withdrawn from the flame just before it catches fire. We find that the middle part of the cardboard does not get burned. This is the part in the zone containing unburnt gas.


(b) If the above experiment is repeated using a wire gauze, we notice that the part in the middle will not become red hot except when the gauze is held in the flame for a long time.


We can prove the presence of unburnt gas in the Bunsen flame. 

This can be done by inserting a glass tube into the flame as shown in figure below



The unburnt gas can be shown to have risen up the tube by putting a light at the top of the tube. The flame will form. This indicates the escape of unburnt gas through the tube.