There are primarily 3 types of temperature scales commonly used to assess the relative warmth or coolness of substances.

Fahrenheit (°F)

The Fahrenheit scale was proposed by Daniel G. Fahrenheit in 1724 . It uses the degree Fahrenheit as the unit and is represented using the symbol °F.

It is based on two fixed points:

  • The freezing point of a saturated salt solution at sea level (14.7 psi or 101.36 kPa)
  • The internal temperature of oxen, which sets the 0 and 100 points on the scale

The Fahrenheit scale was the primary temperature standard for climatic, industrial and medical purposes until the 1960s after which the Celsius scale replaced Fahrenheit. The Fahrenheit scale continues to be used in United States for all temperature measurements including weather, cooking etc.  however for scientific research the scale used is Celsius and Kelvin.

Celsius (°C)

Named after Anders Celsius (1742), this scale sets the freezing and boiling points of pure water at sea level at 0°C and 100°C respectively. The unit is represented using the symbol °C.

The Celsius is one of two temperature scales used in the International System of Units (SI) , the other one being Kelvin.

Kelvin (K) and Rankine (°R)

The Kelvin scale, which primarily finds application in scientific research, is based on the Celsius scale and references absolute zero. It was first proposed and developed by Lord Kelvin and is represented using the symbol K.

The Rankine scale, less commonly used but still encountered, is based on the Fahrenheit scale and also references absolute zero. Absolute zero is the temperature where molecular motion ceases entirely, or where the energy of a molecule is zero. It is represented using the symbol °R and is named after Macquorn Rankine, who proposed it in 1859.

Influence of Pressure and Purity on Water’s Freezing and Boiling Points

The specific freezing and boiling temperatures of water are influenced by pressure changes and the purity of the water. Lower pressure results in a decrease in these temperatures.
These points collectively emphasize the importance and variation in temperature units, crucial for various scientific, engineering, and practical applications.