Structure of a Flame

Structure of a Flame

A flame has three zones:

1. Outermost zone is blue in colour and is the hottest part of the flame. This is also the zone where complete combustion takes place.
2. Middle zone is yellow in colour and is moderately hot. In this zone, partial combustion takes place.
3. Innermost zone is black in colour and least hot. Here, we can find the unburned wax vapours of a candle.

Note: Kerosene oil and molten wax vapourize during burning but charcoal does not produce flame or vapourize when it burns.

Why do goldsmiths blow at the outermost zone of a flame for melting gold and silver?

The outermost zone of a flame is its hottest part. Gold and silver have high melting points and hence, goldsmiths blow at the outermost zone of the flame to melt gold and silver quickly.