When measuring the alcohol amount the person breathes into the device. The same of breath is bubbled in one vial through a mixture of sulfuric acid, potassium dichromate, silver nitrate and water. The principle of the measurement is based on the following chemical reaction:
In this reaction:
The sulfuric acid removes the alcohol from the air into a liquid solution.
Then the alcohol reacts with potassium dichromate to produce:
chromium sulfate, potassium sulfate, acetic acid, and water