Various types of thermometers have been designed to measure temperature. Two of the commonly used thermometers are:
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- The laboratory thermometer: The laboratory thermometer has Celsius scale of temperature. It has 0 degree Celsius as the lower fixed point. This corresponds to the melting point of ice. It has 100 degree Celsius as the upper fixed point. This corresponds to the temperature of boiling water. So it has 10 equal divisions and each division is called one degree.
- The clinical thermometer: The thermometer which is used in our homes or by a doctor for measuring body temperature is called a clinical thermometer. Such a thermometer is a glass0mercury thermometer. It does not have a measure the temperature of ice or boiling water. It can measure only a short range of temperatures from about 35 degree Celsius to 42 degree Celsius. Its range is short because the temperature of human body lies between these two temperatures.
The temperature of the normal human body is 36.8 degree Celsius.
Points to kept in Mind while using a thermometer
- The bulb of thermometer should be completely surrounded by the hot body.
- The thermometer should be protected from sudden changes of temperature. Never wash a hot thermometer in cold water or put a cold thermometer in a hot bath.
- The bulb is the most delicate part of a thermometer and is liable to break easily.
- For correct reading of temperature see that the thermometer is vertically and your eyes are exactly in line with the mercury level.
- Mercury on heating expands. Even a small expansion of mercury in the bulb of the thermometer causes a considerable rise in the capillary tube.
Precautions while using a clinical thermometer:
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While putting the clinical thermometer in the mouth do not press it with your teeth. Hold it simply with the help of your lips. A slight pressure by teeth may result in the breaking of the thermometer bulb and release the mercury in the bulb. Mercury is poisonous.
In case of children, the thermometer should not be put in their mouth. It should be kept under armpit. Half a degree is added to the reading in the thermometer. This gives the body temperature of the patient (child),
The thermometer should be kept vertical. The eyes should be exactly in line with the mercury level.