Dean Rutledge, age 13, of High Point, North Carolina, for his question:
Why does thermometer mercury sometimes look red?
The silvery thread of thermometer mercury fails to perform when the temperature falls below a certain level. But this low down problem did not stump our clever gadgeteers for very long. They simply substituted a substance that has a lower melting point than silvery, metallic mercury. And they colored this temperature measuring material red.
A thermometer that registers temperature with a thread of red material depends upon a thin column of alcohol. Since this liquid material is watery clear in its pure form, it would be invisible inside the glassy clear thermometer tube. So some wid.
A thermometer that registers temperature with a thread of red material depends upon a thin column of alcohol. Since this liquid material is watery clear in its pure form, it would be invisible inside the glassy clear thermometer tube. So some wide awake designer thought of staining the colorless liquid red. This simple addition made the red thread clearly visible beside the precise ladder of degrees on the temperature scale. This simple addition made the red thread clearly visible beside the precise ladder of degrees on the temperature taking thermometer, The coloring used to stain the alcohol, of course, is not an ordinary paint. The coloring used to stain the alcohol, of course, is not an ordinary paint which might tend to settle in a sediment down in the glass bulb at the bottom of the tube. It is one of several dyes that can be relied upon to stain the clear alcohol with a rosy blush and keep it stained indefinitely.
The first thermometers were cumbersome gadgets and their work was limited mostly to two temperature taking duties. As reliable fever reporters, they were a boon to doctors who needed to know for sure whether their paticats were really as sick as they thought they were. In their early days, thermometers also performed as interesting novelties to satisfy the curiosity of weather minded people who wanted to prove that the wintry outdoors was really as cold or as hot as they thought it was. Body temperatures and most weather temperature span a rather narrow range. A column of expanding and contracting mercury was able to solve most of these early problems. The movable metal performed yeoman service for centuries. And we still depend on mercury in many of,our modern thermometers.
A workable gadget is based on a workable principle. And its . principle often can be adapted to perform extended duties. A well made, trusted thermometer is based on the fact that most substances expand when heated and contract when cooled. It has a reservoir of a certain liquid, known to swell and shrink precisely with exact degrees. Changing temperature causes the liquid in the reservoir to rise and fall inside a bored hole in the glass tube. The record is read on a scale of rising degrees marked on or beside the tube. The modern age needed to measure objects hotter and colder than fevers and normal weather temperatures. But the reliable old thread of mercury refused these extra duties, especially the cold ones.
At minus 30 degrees Fahrenheit, liquid mercury freezes solid. When wintry weather dips to this point the silvery thermometer thread cannot budge up or down. But a half mixture of alcohol and water stays liquid down to 58 below zero, This mixture works well in thermometers used in extra cold climates.
Extra gadgets were added to make the reliable old mercury thermometer more useful. Electric wires were sealed into the glass bulb or tube and connected to switches for turning the current on and off. A talented thermometer of this sort can be geared to turn on i3arms, start or stop machines or act as a thermostat. But science and industry need to measure much wider temperature ranges. Some super thermometers use gases under high pressure; others use electric current. Astronomers take the temperatures of the distant heavenly bodies with an electrical gadget of complicated wire loops.