23 May

What is Cold?

We say our freezer temperature is cold.  The ultra low freezers are even colder.  Standard laboratory freezers reach temperatures of – 20°C.  There are two ranges for ultra-low Freezers; -40 to -10°C and -86 to -40°C.  Colder temperatures can be reached in the laboratory using cryo refrigerators for storage in the vapor phase of liquid, nitrogen around -190°C, and cryogenic storage in the liquid phase of LN2 which is lower than the boiling point of LN2, -196°C.

Cold and heat are relative terms and indicate a transfer of energy.  An object is cold because it is pulling energy from the surroundings.  An object is hot because it is giving energy to its surroundings.  Heat is the result of the motion of molecules, the higher the heat, the faster the motion.  There have been many temperature scales designed over the years, most based on the freezing and boiling point of water.   The most common scale since the 1970′s is Celsius (formerly Centigrade) where 0° is the freezing point of water and 100° is the boiling point.  The Fahrenheit scale is still used in the US and Belize.  In the Kelvin scale 0 means absolute zero where all motion of particles cease; this is -273°C or -460°F.  The third law of thermodynamics says it is impossible to reach absolute zero due to the Uncertainty Principle.

The coldest temperature recorded on earth was -89°C  (-129°F) in Vostok, Antarctica – July 1983.

Robin Prymula