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Experiment:To investigate the hottest part of a non-luminous flame.

Answer Text:
To investigate the hottest part of a non-luminous flame.
Requirements
- Bunsen burner, stiff white paper (cardboard), wooden splint.
Procedure
- A bunsen burner is ignited with the air hole open to get a non-luminous flame.
- A piece of white paper (cardboard) is slipped into the flame in region marked
(i) as shown below.
- The piece of paper is removed quickly before it catches fire.
- A fresh piece of paper is then slipped into region marked (ii) as shown below; then again quickly removed before it catches fire.
- The experiment for each of the regions marked (i) and
(ii) is then repeated using wooden splints.
- The splints should be held long enough for some of their parts to get charred
Apparatus

Observations.
- Using pieces of paper.
- In region (i), the part of the paper that was in contact with the flame was charred uniformly as shown below.
- In region (ii), the part of the paper in contact with the flame had a charred ring with an unburnt part in the middle of the ring as shown below
Diagrams

- Using wooden splints.
- In region (i), the part of the splint in contact with the flame was charred uniformly as shown below.
- In region (ii), the part of the splint in contact with the flame had an unburnt part in between two charred regions as shown below.
Diagrams:

Explanations.
- Regions which become charred indicate that they are the hottest part of the flame.
- Region (I) corresponds to the outermost blue region of a non-luminous flame.
- Region (ii) is the almost colourless region of the nonluminous flame, which is however surrounded by the middle greenish blue and the outer pale blue zones.
- Thus in region (i), the uniform charring of the paper and splint indicate that the outer pale blue zone is the hottest part of the flame.
- Similarly the charred ring for experiment in region (ii) show that the parts in contact with the outer pale blue zone gets burnt faster before the parts in contact with the almost colourless or the greenish blue zones.
Conclusions.
- The hottest part of the nonluminous flame is the outermost pale blue zone.
- During heating the object being heated should not be placed nearer the chimney; these parts are less hot.
- For efficient heating the object being heated should be placed at the outermost region of the flame.