Lesson 2

 

Temperature Measurement

Another objective for this lesson is to use the Celsius or centigrade temperature scale to measure the temperature of fluids. Liquids and gases are both fluids.

Thermometers showing degrees F and degrees C. {104tmp22.jpg (29186 bytes)} The laboratory thermometers we have are calibrated in degrees Celsius rather than degrees Fahrenheit.

The Celsius scale used to be called centigrade and I often still call it that. It was called centigrade because the difference between the freezing temperature of water and the boiling temperature of water is divided into 100 degrees. 0oC is defined as the temperature at which water freezes and melts. 100oC is defined as the temperature at which water boils (using normal pressure). It is the scale commonly used in scientific work and in everyday use in most countries.

 Diagram showing Celsius and Fahrenheit scales. {104exTCF.gif (481078 bytes)}
Thermometers showing partial immersion mark. {104tmp23.jpg (23201 bytes)} The laboratory thermometers we use are partial immersion thermometers. This means they are calibrated to read correctly when the end of the thermometer (up to a certain mark) is in the liquid being measured but the temperature scale is not. When you are measuring temperatures, you might want to experiment to see how much difference it makes to vary the depth of the thermometer in the liquid. Thermometer in water to partial immersion mark. {104tmp24.jpg (10186 bytes)}

These thermometers do not have to be shaken down. Quite a few laboratory thermometers have been broken by trying to shake them down next to a table. It is best to hold a thermometer while using it. The container it is in may or may not be able to support it. All you have to do is put the thermometer in the liquid and watch the mercury or alcohol level change. When it stops changing, read the mercury level or the alcohol level if you use one of the red ones. That is your measurement. You don't have to wait a prescribed length of time, just let it come to a rest. 

Two thermometers at about 23. {104tmp25.jpg (24092 bytes)} You may have turn the thermometer to see the numbers and line up the mercury or alcohol with the scale. Two thermometers at about 23.0 (turned). {104tmp26.jpg (23262 bytes)}

 

When you read them you should estimate between the lines. Try to mentally divide the sections into 10 equal parts in order to read to a tenth of a degree.

Now, or when you come to the lab, do Exercise 11.