Entertainment, familiar since childhood, - to heat in a cup with tea the thermometer and to show the reading off scale mercury column to mom. And why mercury? Really, it is well known that metal this poisonous. Dangerously even to hold it at home, and here - to the child an armpit!
Measurement of temperature
There are thermometers liquid, mechanical, electromechanical, electronic, bimetallic, allowing to take temperature at distance and other. Though everything began with the primitive device in which usual air was a working body. Only later it was succeeded by liquids, such as alcohol, glycerin and mercury.
Use as a working body of liquids allowed to increase the accuracy of measurements substantially. On the other hand, application of the same bimetallic plates gave the chance to take measurement in earlier inaccessible ranges. What, in turn, was dictated by requirements of science and the industry. Gradually all thermometers found the niches and areas of application.
So why such dangerous metal nevertheless is used in various including in medical thermometers? It is all about its unique properties. The fact is that, possessing very considerable coefficient of temperature expansion, mercury extends almost linearly, but also it still not everyone. Mercury keeps a stable liquid form in very wide temperature range, from minus 38.8 wasps to plus 375 wasps that allows to use it as working substance practically in any conditions. Strangely enough, the thermometer in which as a working body mercury was used appeared the 17th century. Then began to use also the tinted alcohol, but soon it became clear that at alcohol rather narrow operating range, besides, it extends not linearly. Despite of danger of the mercury thermometer, it was decided to be used as the main device for measurement of temperature. High precision of measurement, within one cell of degree became one of serious arguments in its advantage. That is the level of accuracy of these thermometers such that on them is calibrated by electronic. Important characteristic is also that mercury does not moisten glass, thus, the internal diameter of a tube can be as much as small, and this parameter determines thermometer accuracy. In general at the accurate address even the mercury thermometer is rather safe, poisoning can cause only mercury steam inhalation, and in the itself hermetically soldered device does not represent any danger. The only thing that he demands, it the accurate address.