Difference Between Alcohol and Mercury Thermometers

Alcohol vs Mercury Thermometers

Thermometer is a device used for measuring temperature. It has a temperature sensitive bulb filled with liquid. And there is a scale showing the measured temperature. Normally, temperatures are measured in Celsius degree or Fahrenheit degrees. Thermometers have a narrow capillary tube, which is connected to the bulb with temperature sensitive fluid. As the temperature increases, the fluid expands and rises up the capillary. As the temperature decreases the fluid contracts and goes down in the capillary. The scale along the capillary shows the relevant temperature according to the height of the capillary column. We find the temperature by reading the marker where the meniscus is. The reading can associate with errors for an untrained eye. When using thermometers, there are several precautions to minimize the errors. We should avoid the bulb exposing to unnecessary temperature extremes when taking readings. For example, if we want to measure the room temperature, thermometer should not be placed near a heater as it will give an error. Furthermore, the bulb should not be touched with our hands at any occasion. Thermometer should be stored inside a suitable casing when it is not used. There are different types of thermometers such as alcohol thermometer, mercury thermometer, infra red thermometer, recording thermometer, etc. Among these alcohol and mercury thermometers are commonly used for day to day measurement taking.

Alcohol Thermometer

Alcohol thermometer uses alcohol as the liquid to measure the temperature variations. Alcohol expands when it absorbs temperature and contract in colder temperatures. Most commonly used alcohol in these is ethanol, but different types of alcohols can be used depending on the measured temperature and environment in which the measurements are taken. The measurable temperature range varies according to the used fluid inside the bulb. For example, boiling point of ethanol is 80°C and the freezing point is -115°C. So in an alcohol thermometer containing ethanol, -115°C to 80°C temperature variations can be measured. Alcohol is a colorless, volatile fluid. A dye is used to color alcohol (normally a red dye), so that the reading can be clearly obtained. Because of the volatile nature, the fluid within the bulb can easily evaporate, or can make the liquid column separated. To get accurate readings, this must be avoided. The thermometer should be housed in a casing to protect it from temperature fluctuations.

Mercury Thermometer

A small volume of silver color mercury liquid is used inside the mercury thermometer. Mercury is a highly toxic liquid; therefore, it should be handled with care especially if the thermometer is broken. The freezing point of mercury is -38.83 °C and the boiling point is 357 °C. Therefore, mercury thermometers are best at measuring higher temperatures than the lower temperatures. Thus, this is widely used in laboratories to measure the temperature variations of chemical reactions.

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