Schree Ferguson, age 9, of Waukomis, Oklahoma, for her question:
Where do they find the mercury in thermometers?
Mercury is one of nature's own chemical elements. However, the earth does not have very much of it. It is hidden in special rocks called ore. We find mercury ore in the ground, then we have to separate the silvery metal from other ingredients in the ore.
As a thermometer gets warmer, it is fascinating to watch the thin silvery thread of mercury rise higher in the glass tube. Sometimes the glass gets broken. So let's stop right here for a word of warning. The escaped mercury is even more wonderful than expected. But the wonderful substance is poisonous to touch. The escaped mercury runs around somewhat like water. It may separate into small silvery balls or flow together in bright silvery puddles. However, a sensible young person stays well away from it just in case the poisonous matter touches the flesh.
We tend to think that metals are hard and solid. And so they are, unless they get hot enough to melt. However, the earth has one metal that melts to a liquid at normal temperatures. In fact, it does not freeze solid like other metals until the temperature is 75 degrees below zero.
Precious silver, as we know, is very scarce, and the earth has just about the same scanty amount of mercury. However, we find solid silver in the ground but not solid or even liquid mercury in its pure state.
All the earth's metals are made of tiny atoms and the different kinds of atoms behave in different ways. Mercury atoms like to team up with certain other atoms. They form molecule packages with such atoms as oxygen, chlorine and sulphur. And molecules are very different from their atomic ingredients. For example, mercury and sulphur molecules form a rough, rusty red rock called cinnabar. The silver mercury is there all right, but it is hidden, somewhat like the sugar ingredient is hidden in cake. The rocks in which it hides are called ores. And the best mercury ore is cinnabar colored a lovely shade of red.
The first job is to mine the cinnabar ore from the ground. We don't have to dig very deep because most cinnabar is near the surface. The chunks of ore are carted to a place where they separate the mercury ingredient from the sulphur. The trick is done with currents of hot air passing over the rough, red rocks. The heat draws off the sulphur. It joins with the oxygen in the air and goes off as a choking gas. However the heat is not enough to make the mercury change into gas. So when the sulphur departs, the mercury metal is left behind. This is how they get the shiny mercury to put into those glass tubes for thermometers.
We also use mercury for a lot of other things. We would like to use more of the useful substance, but the earth's supply is very limited. What's more, mercury ores are found only in certain places. California and Nevada have some worth while cinnabar mines. So do China, Italy and Russia but most of the cinnabar is found in Spain.