Liquid thermometers expansion properties

Newton used a liquid in glass-thermometer to study heat radiation. Rumford and Leslie used a difierential gas thermometer. Herschel reverted to the liquid thermometer, but this was soon replaced by the thermopile (Melloni [3.4]). Some time later (Langley [3.5]) the first bolometers were used. More recently the use of the gas thermometer, in the shape of the Golay [3.6] and Luft cells has been reintroduced and is now widely used in spectrometers. Another type of thermal detector now widely used is that utilizing the pyroelectric effect. In addition to these, several other detection processes have been suggested, including thermal expansion and changed dielectric properties with temperature. 

Instruments based on the contact principle can further be divided into two classes mechanical thermometers and electrical thermometers. Mechanical thermometers are based on the thermal expansion of a gas, a liquid, or a solid material. They are simple, robust, and do not normally require power to operate. Electrical resistance thermometers utilize the connection between the electrical resistance and the sensor temperature. Thermocouples are based on the phenomenon, where a temperature-dependent voltage is created in a circuit of two different metals. Semiconductor thermometers have a diode or transistor probe, or a more advanced integrated circuit, where the voltage of the semiconductor junctions is temperature dependent. All electrical meters are easy to incorporate with modern data acquisition systems. A summary of contact thermometer properties is shown in Table 12.3. 

The expansion on heating is most marked in the case of gases, and was noticed first in them as early as 100 b.c., we find this property of gases made use of by Hero of Alexandria in some ingenious experiments. In the case of liquids and solids the expansion is much less noticeable in the latter case it is even somewhat difficult to determine. Gases and liquids are most suitable for the measurement of temperature, and for the construction of temperature measuring instruments, or thermometers, as they are called. 

Thermometers make use of a number of different properties of substances which change with temperature for example, the expansion of a liquid or the variation of electrical resistance. 

Thermal expansion, the change in volume resulting from temperature changes, is a property used in liquid-in glass thermometers. As the temperature of the liquid increases, the liquid expands and fills more of the fine capillary tube on which the temperature scale is engraved. You see the liquid move up the tube and know the temperature is increasing. 

One instrument which measures temperature is a thermometer. This uses the properties of an expanding liquid in a glass tube to indicate a temperature level. Most materials change their dimensions when heated and this property is often used to give a measure of temperature. Many materials expand with an increase in temperature and the rate of expansion varies with different materials. 

Boyle s best-known works include the Spring o/the Air (1660) he discovered that sound does not pass through a vacuum and established that air has weight. He observed the effect of altitude on pressure and the effect of pressure on the boiling point of liquids. He invented a type of thermometer and carried out many experiments on refraction, colour, electricity, relative densities, and the expansion of water when it freezes. He also defined the term element distinguished between mixtures and compounds, and showed that a compound could have different properties from those of its constituents. He was the first to prepare, collect, and burn hydrogen and one of the first to isolate phosphorus in 1680. 

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