Why is only mercury used in clinical thermometer ?
A clinical thermometer is used to measure human body temperature. It consists of a long glass tube which is graduated. A thermometric liquid is present within the tube which expands proportionally to temperature,hence measures it.
Mercury is best suited as a thermometric liquid:
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It expands uniformly when heated.
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It has low specific heat capacity.
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I has a high boiling point (357 °C) and a low freezing point (-39 °C).
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It is a good conductor of heat.
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It does not stick to the walls of the glass tube.
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It is opaque and shiny and hence clearly visible.
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It is available in pure form.