There thermometers, fluid, mechanical, electromechanical, electronic, bimetal, to measure the temperature at a distance, and others.Although it all began with a primitive device, in which the working body was normal air.Only later came to be replaced by a liquid such as alcohol, glycerol and mercury.
use as a working body fluids has substantially increased accuracy.On the other hand, the use of the same bimetallic plates made it possible to measure in previously inaccessible ranges.That, in turn, dictated by the requirements of science and industry.Gradually, all the thermometers have found their niches and areas of application.
So why such a dangerous metal is still used in various, including medical thermometers?It's all about
its unique properties.The fact is that, with very significant coefficient of thermal expansion, mercury expands almost linearly, but that's not all.Mercury has maintained a stable liquid form over a very wide temperature range, from minus to plus 375oS 38,8oS that allows you to use it as a working material in virtually any environment.
Ironically, thermometer, in which the working medium used mercury, appeared the XVII century.At the same time we began to use alcohol and stained, but it soon became clear that alcohol is narrow operating range, in addition, it does not expand linearly.
Despite the risk of a mercury thermometer, it was decided to use as the primary device for measuring the temperature.One of the major arguments in its favor was the high measurement accuracy within a hundredth of a degree.That is the level of accuracy of these thermometers, so that it is on them calibrated electronic.
important characteristic is the fact that the mercury does not wet glass, thus, the inner diameter of the tube can be arbitrarily small, and the parameter determines the accuracy of the thermometer.
Overall, even with careful handling mercury thermometer is safe enough, in fact poisoning can cause only inhalation of mercury vapor, and by itself is hermetically sealed device does not pose any danger.The only thing it requires is handled with care.