WHAT IS FLAME?
Observe an LPG flame. Can you tell the colour of the flame. What is the colour of a candle flame?
Recall your experience of burning a magnesium ribbon in Class VII. If you do not have experience of burning the remaining items in Table 6.2 you can do that now.
Figure 6.8: Colours of a candle flame and the flame of a kitchen stove
Figure 6.9: Flames of kerosene lamp, candle and Bunsen burner
Record your observations and mention whether on burning the material forms a flame or not.
Table 6.2: Materials forming Flame on Burning
Source: This topic is taken from NCERT TEXTBOOK
STRUCTURE OF A FLAME
Activity 6.5:
* Light a candle (Caution : Be careful).
* Hold a 4-5 cm long thin glass tube with a pair of tongs and introduce its one end in the dark zone of a non-flickering candle flame (Fig. 6.10).
* Bring a lighted matchstick near the other end of the glass tube.
* Do you see a flame caught at this end of the glass tube after a while?
* If so, what is it that produces a flame?
* Notice that the wax near the heated wick melts quickly
Figure 6.10:
The substances which vapourise during burning, give flames. For example, kerosene oil and molten wax rise through the wick and are vapourised during burning and form flames. Charcoal, on the other hand, does not vapourise and so does not produce a flame. In Activity 6.5, could the vapours of wax coming out of the glass tube be the cause of the flame produced?
Figure 6.11:
When the candle flame is steady, introduce a clean glass plate/slide into the luminous zone of the flame (Fig. 6.11). Hold it there with a pair of tongs for about 10 seconds. Then remove it. What do you observe?
Figure 6.12:
A circular blackish ring is formed on the glass plate/slide. It indicates the deposition of unburnt carbon particles present in the luminous zone of the flame.
Hold a thin long copper wire just inside the non-luminous zone of flame for about 30 seconds (Fig. 6.12).
Notice that the portion of the copper wire just outside the flame gets red hot. Does it indicate that the non-luminous zone of the flame has a high temperature? In fact, this part of the flame is the hottest part (Fig. 6.13).
Figure 6.13: Different zones of candle flame
Goldsmiths blow the outermost zone of a flame with a metallic blow-pipe for melting gold and silver (Fig. 6.14). Why do they use the outermost zone of the flame?
Figure 6.14: Goldsmith blowing through a metallic pipe
Source: This topic is taken from NCERT TEXTBOOK