Physical Science

Experiment 3-1

Temperature During Freezing


Background Information

Humans have long known that ice and snow melt, and that occasionally water freezes solid.  But early explanations for those processes differ from our best current explanations.  Over 2400 years ago the Greeks proposed that the material of our world could be air, water, earth, or fire.  A rough translation of what they meant might be gaseous, liquid, solid, or energy.  They called these elements but intended more a notion of basic, fundamental properties than our current notion of elements being fundamental materials.  But that distinction was probably beyond their understanding.  The Greeks suggested that with appropriate techniques, a material made of predominately one element (say liquid water) could be transformed into another element (perhaps solid earth).  It is that sort of process we wish to investigate.

In the late 18th Century, Frenchman Antoine Lavoisier and wife Marie were among the first to suggest that the transformation from earth to water to air was not a change in fundamental material but rather a change in the state (or properties) of the same matter from solid to liquid to gaseous caused by providing heat.  And Lavoisier suggested the process could be reversed by removing heat.  (Lavoisier did continue to believe that heat was one of the fundamental substances, but he proposed a new name, caloric).thermometer

We will eventually want to distinguish heat, the flow of energy (sometimes calculated in calories), from temperature, a measure of heat content in material.  But even this distinction will be somewhat confusing because when heat flows into material, not all of it is measurable by an increase in temperature.  But we will leave those details for much later.

We have always been able to roughly measure temperature using nerves in our skin.  Several additional methods of measuring temperature have been developed.  It has long been appreciated that generally the volume of materials expands when heat is added.  But different materials expand volume at different rates.  Many liquids expand at a higher rate than glass.  So early equipment makers such as Gabriel Fahrenheit (1686-1736), René Antoine Ferchauld de Réamur (1683-1757), Anders Celsius (1701-1744) and Jean Pierre Cristin (1683-1755) calibrated glass tubes containing liquids as temperature measuring devices called thermometers.  By capping a relatively large amount of liquid with a neck of tiny diameter, the meniscus rise due to expanding volume can be greatly exaggerated.

Other properties of material also change with temperature.  For example several electrical properties change with temperature so that electrical measuring devices can be calibrated to measure temperature differences.

Arbitrary scales have been established to calibrating measuring devices.  Fahrenheit experimented with several methods.  One story (a favorite of this author) suggests that Fahrenheit, wanting a calibrated scale for measuring weather, chose a mixture of half salt and half melting ice as a low temperature which he defined as 0, and the higher temperature of a living creature, perhaps a cow, which he defined as 96 facilitating dividing the differences six times to create intermediate scale marks.  Whether completely accurate history or not, the difficulty of developing a convenient calibrated scale is apparent.  Finding a cooperative animal could be a challenge.  And a 50%/50% mixture of salt and ice promptly starts to melt changing the intended composition and resulting temperature calibration.  Cristin later developed a calibration scale with melting ice set as 0 and boiling water set as 100, a scale now named after Celsius.


For this and many later experiments you will need to purchase or construct a thermometer which can measure temperatures over a range from a bit colder than freezing water to a bit warmer than boiling water (-10 to 110°C).  Since nearly all the world has agreed to a set of standard measuring units called the System International (SI) which includes the Celsius scale, it would be desirable for us to use a thermometer calibrated in Celsius units.  Traditional glass thermometers are available for only a few dollars.  However a slightly more expensive electronic thermometer which has a long narrow temperature probe might be more useful.  It is possible to construct a very precise, low cost electronic thermometer from an inexpensive electronic sensor wired to a low cost electronic multimeter.  (National Semiconductor LM35 produces 10 millivolts per degree Celsius over the range desired.  While it comes in various grades, only the least expensive is needed.  If you choose to assemble your own thermomenter you will need to calibrate it.)

  1. Construct a suitable apparatus by placing a small flower pot with an open bottom hole so that it can drain without causing problems.

  2. Prepare a smaller container to fit inside, holding a thermometer and surrounded by a pure substance to be investigated, in this case water.

  3. Fill the space between the inner container and the outer flower pot with a mixture of crushed ice and equal amount of table salt.

  4. As soon as the apparatus and materials are assembled, begin to measure and record the temperature every 20 or 30 seconds.

  5. Allowing the water from the melting ice to escape, continue to record the temperature of the pure water until considerably after the water has frozen solid.

  6. Construct a line graph of the temperature verses time.  Refer to the next activity for details about constructing the graph of your results to visualize any pattern in your measurements.

No measurement is perfect, but it helps to try to obtain the best measurements possible from our equipment.  Most people have a bias preferring whole numbers and sometimes even multiples of ten.  But the calibrated scales on our thermometers are number lines with most values in between whole numbers.  So if we unintentionally round off to the nearest whole number, we discard information that may be important.  Always try to measure and record one decimal place MORE than the scale marks.  For most thermometers this means estimate and record tenths of degrees.

Record in your science journal the mass measurements, first in table format, then by constructing a line graph.  Write a Formal Report if you need to earn credit.


to next activity
to Physical Science menu
to site menu

created 11/16/2003
revised 11/20/2003
by D Trapp
Mac made