1. Take some ice in a beaker. Immerse a thermometer in ice for two minutes. Mark the Mercury level. Now let the ice melt.
2. The level of Mercury remains same while ice melts. This means that temperature is constant.
3. This constant temperature at which ice melts is called melting point of ice and mark it 0 °C.
4. Take some water in a beaker. Immerse the thermometer in it and start heating the water. It will start boiling while getting converted into steam.
5. Mercury level starts rising and reaches a point beyond which it doesn’t rise. Mark the level of mercury at this point.
6. Observe the constant level at which Mercury stays while water is boiling, this constant temperature is called boiling point of water. We mark the level of mercury at this point as 100 °C.
7. Thus temperature at which ice melts or water boils is constant. These values are fixed as 0 °C and 100 °C respectively. Like water, all substances in pure form melt and boil at certain fixed temperatures.
8. To create a scale, we need two fixed points. Let us choose the melting point (0 °C) and boiling point (100 °C) as two fixed points for the scale of thermometer. Now divide the distance between these two points on the thermometer into 100 equal parts.
9. Each of the 100 equal parts represents 1 °C. We further divide 1 °C into 10 small divisions. It can be read as 1/10 = 0.1 °C.
