Abstract: A method for determining the gas content of a person's breathing air, comprises, first determining when the breathing air is at a condition in which best testing results will be effected. This is done by arranging a capacitor in a breathing tube through which the breathing air is directed. The capacitor is first heated to a predetermined temperature and the breathing air is directed over it so as to cool it until it has attained a predetermined temperature change. This temperature change is such that it will take place when the person's breathing air has its desired constituency. When this occurs, the breathing air is then directed into a test chamber in which it is tested to determine the constituency of the breathing air particularly the percentage of alcohol which it contains.

Abstract: A method of determining and separating the alveolar air proportion of a person's breathing air and thereafter measuring a proportion of a desired gas component thereof, comprises, conveying the exhaled air at a minimum velocity through a conduit, continuously measuring the temperature of the conveyed air, and when the variation in temperature which is measured drops below a predetermined threshold value, directing the exhaled air into a measuring chamber using a sensor device in the measuring chamber to determine the proportion of the desired gas component. A device for this purpose, comprises, a breathing tube which has a passage therethrough for the passage of the breathing air and has a first direct passage terminating in a first outlet to ambience and a second branch passage which passes through a measuring chamber for alveolar air is connected downstream of the measuring chamber to ambience.