Fahrenheit did not define 32° as the freezing point of water. Instead, he defined 0° as the freezing point of a water and salt mixture. Since salt lowers the freezing point of water, the freezing point for this mixture was lower than it would have been for plain water. Upon defining the degree intervals between the freezing and boiling points of the water and salt mixture, and he found that water itself freezes at 32°F.