What is foarnite mixture? How can it extinguish fire?

Explanation

Foam type fire extinguishers are nowadays used to extinguish petroleum and other oil-fires. To produce stable foam of `CO_2` , a mixture consisting of a concentrated solution of aluminium sulphate and sodium bicarbonate along with licorice extract is used. This mixture is called foamite mixture.
`Al_2(SO_4)_3` on hydrolysis produces `Al(OH)_3 and H_2SO_4`. Sulphuric acid thus obtained reacts with `NaHCO_3` to liberate bubbles of `CO_2`. These `CO_2` bubbles form stable sticky foam with `Al(OH)_3` in the presence of licorice extract. This foam, when applied on the fire, forms a layer and prevents the oil or petrol from coming in further contact with air or oxygen. Consequently, the fire gets extinguished.
`Al_2(SO_4)_3 + 6NaHCO_3 to 2Al(OH)_3 + 3Na_2SO_4 + 6CO_2uarr`