Two reasons really.
1. As a metal it is highly conductive to heat and will therefore react quickly and accurately to an applied heat source.
2. It is "non-wetting". (Look at how mercury sits in a tube as opposed to water). This allows accurate gradients to be marked off as there will be a definite edge to the mercury, rather then the fuzzy edge you get with water.
2006-12-03 23:43:53
·
answer #1
·
answered by the_lipsiot 7
·
0⤊
0⤋
In 1714, Gabriel Fahrenheit (1686-1736) invented the mercury-in-glass thermometer, shown at the left. This instrument depends on the volume thermal expansion of mercury, or actually the expansion of the mercury relative to glass. If they both expanded at the same rate, the length of the mercury column would not change. Mercury not only expands much more rapidly than glass, but its expansion is fairly uniform, so it is a good thermometric substance. The sensitivity of the thermometer depends on the ratio of the reservoir volume to the square of the inside diameter of the stem. The formula is shown, where β is the coefficient of relative thermal expansion.
Thermometer design is a relatively simple matter. We measure the thermal expansion of a volume V of liquid by its expansion into a capillary of cross-sectional area A. Since the coefficient of cubical expansion is β = (1/V)(dV/dT), and dV = Adx, where x is the length of liquid in the capillary, the sensitivity of the thermometer, dx/dT = β(V/A). For β, we use the difference of the cubical expansion coefficients of the liquid and glass. Thermometers are not affected by vapor pressure above the capillary column, as a barometer would be. It is only necessary that the liquid be clearly distinguishable from the volume above the liquid. The glass capillary magnifies the column, and can be shaped to increase the magnification.
Mercury has β = 0.181 x 10-3 per °C, while ordinary soda-lime glass has β = 0.0276 x 10-3 per °C. The β of most liquids is on the order of 10-3, while that of most solids is about 10-5, so the solid expansion is only about 1% of that of the liquid. For mercury, the difference is β' = 0.153 x 10-3 per °C. Suppose our thermometer has V = 250 mm3, with a capillary bore of 0.2 mm. The sensitivity will be dx/dT = 1.22 mm/°C, so a scale reading from -10°C to 110°C will be 158 mm long. This is actually fairly typical of small mercury thermometers. Mercury melts at -38.87°C, and boils at 356.7°C, so it is useful over a wide range. A mercury column is also very easily seen.
etc,,,
2006-12-04 08:21:50
·
answer #2
·
answered by veerabhadrasarma m 7
·
0⤊
0⤋
http://en.wikipedia.org/wiki/Mercury_%28element%29
go here lots of info.
2006-12-04 07:44:28
·
answer #3
·
answered by Anonymous
·
0⤊
0⤋