Page 72 - Science Class 08
P. 72
These are as: monoxide gas which is poisonous. It is,
v Combus ble substance therefore, people are advised not to keep
angithi in a closed room while sleeping.
v Supporter of combus on (oxygen)
v Igni on temperature Igni on Temperature
You have already studied about igni on tempe-
Combus ble Substances
rature in previous chapter. However, let us take
There are certain substances which catch fire an overlook of it again.
easily and give a lot of heat. These substances
The minium temperature at which a substance
are called combus ble substances.
catches fire and starts burning is referred to as
For example, wood, twig, paper, cloth, alcohol, the igni on temperature of the substance.
kerosene, oil, petrol, diesel, wave, LPG,
Igni on temperature of different combus ble
CNG, etc.
substances is different. The substances which
have very low igni on point are called highly.
combus ble or highly inflammable
substances. These substances should be
Make a list of combus ble and non-
combus ble substances you can see in your handled with extra care.
home. Some substances have extremely low igni on
point that can catch fire even at room tempe-
Combus ble Non-combus ble
rature.
______________ _______________
For example, phosphorus can catch fire even at
______________ _______________ room temperature. Therefore, phosphorus is
______________ _______________ kept in kerosene or water.
______________ _______________ TYPES OF COMBUSTION
We can categorise combus on in the following
types:
SUPPORTER OF COMBUSTION
v Spontaneous Combus on
Air (oxygen) is the supporter of combus on.
v Rapid Combus on
Without oxygen no combus ble object can catch v Slow Combus on
fire. You might have seen chulha which are used
Spontaneous Combus on
generally in rural areas for cooking food. Wood
Some mes, combus on starts without igni ng
or coal are used in those kind of chulha. If you
carefully observe the arrangement of logs of a combus ble substances. This combus on is
known as spontaneous combus on. It happens
wood or pieces of coal, you will find that they
with the combus ble substances having
are arranged in such a way keeping gaps in igni on temperature lower than the room
between them to allow air to enter the chulha.
temperature, i.e., about 35°C.
If these gaps are not le , the wood may begin For example, a ribbon of phosphorus catches fire
to release a lot of smoke. This is a sign of as soon as it is brought out at room temperature
incomplete combus on. It is due to insufficient (35°C). It is therefore, phosphorus is kept in
supply of oxygen. Due to incomplete combus- kerosene oil.
on, combus ble substances release carbon
72 Science-8
