When a volatile chemical (alcohol) is dissolved in a liquid (blood) and is
brought to equilibrium with air (alveolar breath), there is a fixed ratio bet
ween the concentration of the volatile compound (alcohol) in air (alveolar
breath) and its concentration in the liquid (blood), and this ratio is constant
The temperature at which the breath leaves the mouth is normally 34°C.
At this temperature, the ratio of alcohol in the blood to alcohol in alveolar air is
approximately 2,100 to 1. In other words, 1 milliliter of blood contains nearly
the same amount of alcohol as 2,100 milliliters of alveolar breath. Henry’s law
thus becomes a basis for relating breath to blood-alcohol concentration.
