On the Fahrenheit temperature scale, the freezing point of water is 32 degrees. Fahrenheit observed this by placing a thermometer in an equal mixture of water and ice.
Daniel Fahrenheit wanted to expand the Roemer temperature scale, at which 0 marked water's freezing point and 60 marked its boiling point. He multiplied those values by four but also adjusted the position of 0 to mark an equal mixture of ammonium chloride, water and ice. Taking ammonium chloride out moved the freezing point of water, and the approximate body temperature at 96 degrees, based on putting the thermometer beneath his wife's armpit. After Fahrenheit's passing, scientists recalibrated the scale, setting the precise freezing and boiling points of water at 32 and 212, respectively, and establishing standard body temperature at 98.6.