Preheating zone:

Immediately above the basic reaction zone lays the third or interconal zone or the reaction free zone that could extend up to considerable height. A maximum temperature is achieved just above the tip of the inner zone. A higher temperature favours both types of production of free atoms and maximum excitation for atomic emission spectroscopy. Thus, this zone is used for flame photometry.

The outermost fourth zone is the secondary reaction zone. Inside this zone, the products of the combustion procedures are burnt to stable molecular species through the surrounding air.

The shape of an unmixed flame is commonly different. The inner zone could still be recognised, but it is extremely vague and is thickened. The laminar flame makes a strong hissing noise that gets louder when a liquid is atomised within it. We shall now look into the reactions that are taking place while the element is placed within flame.