Thermometer

A thermometer is a apparatus which is used to measure Température S. It is the field of study of the Thermométrie.

Actually, a thermometer measures its own temperature (that of its part which is used to make measurement). This temperature is that of the ambient conditions only if there is thermal balance between the thermometer and the ambient conditions.

That means for example, which if thermometer is exposed to the Sun, it will be hotter than the air, and than this variation in temperature will depend entirely on its color and its ventilation, and thus that a temperature measured under these conditions is completely whimsical compared to the temperature of the Air. (Therefore the meteorologists measure the temperature under ventilated shelter.)

The measurement of the temperatures can be based on the Dilatation of the bodies (solid, liquid or gas), or any other physical property (electric variations in the case of Thermocouple, color of emission of light for the high temperatures, etc) according to the temperature. This general principle is put pursuant to very diverse ways according to the needs (beaches of temperatures to be measured, nature of materials studied, etc). The usual thermometers with liquid are the mercury thermometers and the thermometers with alcohol.

The applications of the thermometers are multiple, in Météorologie, Médecine, for the regulation, in the industrial processes, etc

History

The first thermometer was the Thermoscope of Galileo, invented in 1597.

Rene-Antoine Ferchault de Réaumur built in 1730, the first thermometer with “spirit of wine”, old denomination of ethanol. About the middle of the 18th century, two types of mercury thermometers received a centesimal division between the melting point of the ice and the boiling point of water.

The Swedish physicist Anders Celsius made build in 1741 a thermometer with mercury, which marked 100 degrees at the point of boiling and 0 at the freezing point of the water and which was used of 1742 to 1750 at the observatory of Upsal. At the same time, the perpetual secretary of the Academy of the Art schools of Lyon, Jean-Pierre Christin (1683-1755), made build by the Lyons craftsman Pierre Casati a mercury thermometer on ascending centesimal scale, which it submitted on March 19th, 1743 to the public assembly of this Academy.

The Swedish thermometer the Centigrade one and the Lyons thermometer of Casati would have had only one restricted use if the French revolution had not given to the modern world the metric system, and if the Commission of the weights and measures, created by Convention, had not decided into 1794 that “the thermometric degree will be the hundredth left the distance between the term of the Glace and that of the ebullient water”.

In 1702, the astronomer Danish Ole Roemer (1644 - 1710) manufactures an alcohol thermometer marking ebullient water with 60° and freezes it crushed with 7,5°. In 1717, the German scientist Fahrenheit (1686 - 1736) replaces alcohol by mercury. He fixed at 32° the temperature of the melting ice and at 96° the normal temperature of the Sang. He gives to the thermometer his final form.

In 1730, Réaumur, physicist and naturalist French, built the alcohol thermometer for which it used the scale 0-80. Centigrade Anders, physicist Swedish (1701 - 1744) built in 1742 a mercury thermometer which marked 100° at the point of boiling of water and 0° at the freezing point of water. But in 1745, Carl von Linné (1707 - 1778) reversed the scale of the temperatures and presented to the Swedish Academy a mercury thermometer which marked 0° for the melting ice and 100° for ebullient water.

In 1794, Convention decided that the “thermometric degree would be the hundredth left the distance between the term of the ice and that of ebullient water”. In October 1948, the name of degree Celsius was chosen by IXe International Conference of the Weights and Mesures.

In France the clinical thermometers with mercury are prohibited with the sale since March 1st 1999 by a decree of the December 24th 1998.
And to reinforce this measurement, a ministerial circular prohibited the use of this kind of thermometers in the French hospitals since September 1999.
At this date, one estimated at more than 15 million the number of mercury thermometers of use in the French households. The same source indicated that it took several years so that this impressive stock is gradually replaced by electronic thermometers (manufactured in China) or with Infrarouge (of American origin), designed like substitute products since the years 1970.

Risk for health

The reproach made with the mercury thermometer holds in particular in what it would represent a danger in the event of breaking. What very frequently arrives to the private individuals and in hospital medium. Not without neglecting “the infectious risks related to the cleaning insufficient of the apparatus, but nonspecific to the mercury thermometer”, the risk related to breaking is more to fear. Breaking is dependant is with handling (at the time of the " secouage" for the handing-over of the thermometer with zero), that is to say with the movements of the patient at the time of a taking of correct temperature which required several minutes. The instrument can be " oublié" and being broken inadvertently by the patient.

The specialists note that these breakings, pain-killers of appearance, “cause rejections mercuriels likely to affect health”. These same specialists advance as the breaking of a thermometer with mercury can cause local traumatic lesions (perforations…) and of the cutaneous wounds. These wounds will remain benign “as long as it there not of contact with mercury.” In the event of contact, there are an inflammatory reaction and a toxic risk. The other direct risk, it is the mercury ingestion by a child.

It is also indirect risks by the means of the mercury vapors. This risk which appears normally limited taking into account volume concerned (a thermometer containing approximately 2 grams of mercury, is 0,1 Cm3) is especially to fear in the sick rooms, i.e. in closed circles, little aired, heated… In this precise case, a breaking of thermometer releases from the toxic vapors directly inhaled by the occupants of the room. Of the similar circumstance, worst of the solutions would consist in using the vacuum cleaner. The machine will heat mercury then; will vaporize and recontaminera other parts with each use, according to proportions related to the dimension of the part concerned.

Models of thermometers

Measuring units

There exist thermometers giving of the temperature measurements in the three great systems: degrees Centigrade, Kelvin S, degrees Fahrenheit. However, it is advisable to point out that the measuring unit of reference is the Kelvin, used in the international Système.

See too

Simple: Thermometer

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