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Mercury in glass

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The thermometer was used by the originators of the Fahrenheit and Celsius temperature scales.

Anders Celsius devised the Celsius scale, which was described in his publication the origin of the Celsius temperature scale in 1742.

Celsius used two fixed points in his scale: the temperature of melting ice and the temperature of boiling water. This wasn't a new idea, since Isaac Newton was already working on something similar. The distinction of Celsius was to use the melting temperature and not the freezing temperature. The experiments for reaching a good calibration of his thermometer lasted for 2 winters. By performing the same experiment over and over again, he discovered that ice always melted at the same calibration mark on the thermometer. He found a similar fixed point in the calibration of boiling water vapour (when this is done to high precision, a variation will be seen with atmospheric pressure). At the moment that he removed the thermometer from the vapour, the mercury level climbed slightly. This was related to the rapid cooling (and contraction) of the glass.

The air pressure influences the boiling point of water. Celsius claimed that the level of the mercury in boiling water is proportional to the height of the barometer.

When Celsius decided to use his own temperature scale, he originally defined his scale "upside-down", i.e. he chose to set the boiling point of pure water at 0 °C (212 °F) and the freezing point at 100 °C (32 °F).[1] One year later Frenchman Jean Pierre Cristin proposed to invert the scale with the freezing point at 0 °C (32 °F) and the boiling point at 100 °C (212 °F). He named it Centigrade.[2]

Finally, Celsius proposed a method of calibrating a thermometer:

Place the cylinder of the thermometer in melting pure water and mark the point where the fluid in the thermometer stabilises. This point is the freeze/thaw point of water.
In the same manner mark the point where the fluid stabilises when the thermometer is placed in boiling water vapour.
Divide the length between the two marks into 100 equal pieces.
These points are adequate for approximate calibration but both vary with atmospheric pressure. Nowadays, the triple point of water is used instead (the triple point occurs at 273.16 kelvins (K), 0.01 °C).

thermometer
A special kind of mercury thermometer, called a maximum thermometer, works by having a constriction in the neck close to the bulb. As the temperature rises the mercury is pushed up through the constriction by the force of expansion. When the temperature falls the column of mercury breaks at the constriction and cannot return to the bulb thus remaining stationary in the tube. The observer can then read the maximum temperature over a set period of time. To reset the thermometer it must be swung sharply. This is similar to the design of a medical thermometer.

Physical properties
Mercury will solidify (freeze) at -38.83 °C (-37.89 °F) and so may only be used at higher temperatures. Mercury, unlike water, does not expand upon solidification and will not break the glass tube, making it difficult to notice when frozen. If the thermometer contains nitrogen the gas may flow down into the column and be trapped there when the temperature rises. If this happens the thermometer will be unusable until returned to the factory for reconditioning. To avoid this some weather services require that all mercury thermometers be brought indoors when the temperature falls to -37 °C (-34.6 °F). In areas where the maximum temperature is not expected to rise above -38.83 °C (-37.89 °F) a thermometer containing a mercury-thallium alloy may be used. This has a solidification (freezing) point of -61.1 °C (-78 °F).

Phase out in North America
Today mercury thermometers are still widely used in meteorology, however in other usage they are becoming increasingly rare, as many countries have banned them outright from medical use[citation needed]. Some manufacturers use galinstan, a liquid alloy of gallium, indium, and tin, as a replacement for mercury.

The typical "fever thermometer" contains between 0.5 to 3 g (.3 to 1.7 dr) of elemental mercury.[3] Swallowing this amount of mercury would, it is said, pose little danger but the inhaling of the vapour could lead to health problems.[4]

In the United States both the American Academy of Pediatrics[5] and the United States Environmental Protection Agency[6] recommend that alternative thermometers be used in the home.[7]

Mercury probe

The Mercury Probe is an electrical probing device to make rapid, non-destructive contact to a sample for electrical characterization. Its primary application is semiconductor measurements where time-consuming metallizations or photolithographic processing are required to make contact to a sample. These processing steps usually take hours and have to be avoided where possible to reduce device processing times.

One of the first successful Mercury Probe applications was the characterization of epitaxial layers grown on silicon [1]. It is critical to device performance to monitor the doping level and thickness of an epitaxial layer. Prior to the Mercury Probe, a sample had to undergo a metallization process, which could take hours. A Mercury Probe connected to capacitance-voltage doping profile instrumentation could measure an epitaxial layer as soon as it came out of the epitaxial reactor. The Mercury Probe formed a Schottky barrier of well-defined area that could be measured as easily as a conventional metallized contact.

Another Mercury Probe application popular for it speed is oxide characterization [2]. The Mercury Probe forms a gate contact and enables measurement of the capacitance-voltage or current-voltage parameters of the mercury-oxide-semiconductor structure. Using this device, material parameters such as permittivity, doping, oxide charge, and dielectric strength may be evaluated.

A Mercury Probe with concentric dot and ring contacts as well as a back contact extends Mercury Probe applications to [SOI] structures, where a pseudo-MOSFET device is formed [3]. This Hg-FET can be used to study mobility, interface trap density, and [transconductance].

The Mercury Probe applies mercury contacts of well-defined areas to a flat sample. The nature of the mercury-sample contacts and the instrumentation connected to the Mercury Probe define the application. If the mercury-sample contact is ohmic (non-rectifying) then current-voltage instrumentation can be used to measure resistance, leakage currents, or current-voltage characteristics. Resistance can be measured on bulk samples or on thin films. The thin films can be composed of any material that does not react with mercury. Metals, semiconductors, oxides, and chemical coatings have all been measured successfully [4].

The same mercury-sample structures can be measured with capacitance-voltage instrumentation to monitor permittivity and thickness of dielectric materials. These measurements are a convenient gauge for development of novel dielectrics of both low-k and high-k types.

If the mercury-sample contact is rectifying then a diode has formed and offers other measurement possibilities. Current-voltage measurements of the diode can reveal properties of the semiconductor such as breakdown voltage and lifetime. Capacitance-voltage measurements allow computation of the semiconductor doping level and uniformity. These measurements are successfully made on many materials including SiC, GaAs, 2DEG, GaN, InP, CdS, and InSb.

The ability of the Mercury Probe to form rapid, non-destructive, contacts to planar materials makes it a versatile tool for investigation of many parameters of a wide range of conducting, insulating and semiconductor materials.

Mercury switch
A mercury switch (also known as a mercury tilt switch) is a switch whose purpose is to allow or interrupt the flow of electric current in an electrical circuit in a manner that is dependent on the switch's physical position or alignment relative to the direction of the "pull" of earth's gravity.

Mercury switches consist of one or more sets of electrical contacts in a sealed glass envelope which contains a bead of mercury. The envelope may also contain air, an inert gas, or a vacuum. Gravity is constantly pulling the drop of mercury to the lowest point in the envelope. When the switch is tilted in the appropriate direction, the mercury touches a set of contacts, thus completing the electrical circuit through those contacts. Tilting the switch the opposite direction causes the mercury to move away from that set of contacts, thus breaking that circuit. The switch may contain multiple sets of contacts, closing different sets at different angles allowing, for example, Single-Pole, Double-Throw (SPDT) operation
Roll sensing
Tilt switches may be used for a rollover or tip over warning for construction equipment and lift vehicles operating in rugged off-highway terrain. There are several non-mercury types but few are implemented due to sensitivity to shock and vibration - causing false tripping. However devices resistant to this do exist. Yahoo: bimetal thermometer Mercury in glass What Is a Mercury Thermometer
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