Estimating alcohol concentration
The accurate measurement of blood alcohol concentration (BAC) has been a cornerstone in the study and regulation of alcohol consumption. While the "Widmark Micromethod," developed by Swedish chemist Erik M. P. Widmark in 1914, became an established forensic test in Europe, the United States continued to rely predominantly on behavioral evidence until mid-20th century innovations.
Alcometer
Developed in 1941 by Leon Greenberg at Yale, the Alcometer represented a major step forward in the practical measurement of blood alcohol content. Unlike earlier theoretical models, such as Widmark’s formula, the Alcometer offered real-time results through a portable breath-testing device. It was one of the “first-generation” breath-alcohol analysis instruments introduced during that era, alongside the Drunkometer and the Intoximeter. Although Greenberg's invention was innovative, the Drunkometer, created a decade earlier by Rolla N. Harger at Indiana University, became the first breath-test device widely adopted by law enforcement.
The Alcometer (also referred to as the Alcoholometer) operated by mixing a person’s deep-lung breath with iodine pentoxide. If alcohol was present, a chemical reaction released iodine, which, when absorbed into a starch solution, changed color in proportion to the alcohol concentration. This provided a practical complement to Widmark’s theoretical calculations, and the results closely matched those from direct blood analysis.
While eventually replaced by the more advanced Breathalyzer in 1954, the Alcometer played a critical role in establishing breath testing as a scientifically valid method for detecting alcohol impairment. Greenberg’s work also helped confirm the relationship between breath and blood alcohol levels, laying the groundwork for future developments in the field.
Read more
- Greenberg, L. A., & Keator, F. W. (1941). A portable automatic apparatus for the indirect determination of the concentration of alcohol in the blood. Quarterly Journal of Studies on Alcohol, 2(1), 57–72.
Leon Greenberg's Alcometer
A portable breath-testing device, the Alcometer (sometimes called Alcoholometer) was one of three “first-generation” breath-alcohol analysis devices. It was invented by Leon A. Greenberg at the Yale Applied Physiology Lab, the home of the Section of Alcohol Studies.
Leon A. Greenberg (1907-1985) with his invention, the Alcometer
A widely circulated image of Greenberg testing the Alcometer was originally an AP Newsfeatures photo by World Wide Photos from 1942.
Alcometer in use
The device analyzed the breath for alcohol by mixing the alveolar air in one’s deep breath with iodine pentoxide. If there was alcohol in one’s system, its color changed in proportion to the amount of alcohol present. Results obtained showed a high correlation with direct blood analysis. Source: the 1951 issue of SSAS Alumni News, an annual newsletter of the Summer School of Alcohol Studies.
The inventor with his invention
Clipping from a Yale Center of Alcohol Studies promotional flyer from 1953.
Alco-Calculator
The Alco-Calculator is a cardboard slide-rule, which estimates one’s blood alcohol concentration given the quantity of alcohol consumed, body weight, and hours since beginning alcohol consumption. Created by Leon A. Greenberg, this simple device came with an instruction manual.
It was distributed by the Center of Alcohol Studies Publication. There are a few copies still available and in use in 2025. As described in the description in the Publication Catalog:
The alco-calculator is a handy slide rule which estimates blood alcohol concentration. The slide rule contains complete instructions to
(1) estimate the amount (percent) of alcohol in the blood after drinking known amounts of beverages;
(2) estimate the minimum number of drinks consumed from the concentration of alcohol in the blood;
(3) calculate and compare the alcohol values by the number of drinks of different types of beverages;
(4) estimate the concentration of alcohol over time; and
(5) estimate the time necessary for a particular concentration to fall to a desired level.
One side of the slide calculates the blood alcohol values for men, the other side, for women. Includes revisions by David Lester.
Alco-calculator (front)
The Alco-calculator is a cardboard slide-rule, which estimates one’s blood alcohol concentration based on the quantity of alcohol consumed, body weight, and hours since beginning alcohol consumption.
Alco-Calculator (back)
The back of the alco-calculator has instructions on how to use it. See also the Instruction Manual from 1983 for more details.
The Alco-Calculator: an educational instrument advertised in the Summer School of Alcohol Studies Alumni News in 1983
The rule can be moved left (for males) or right (for females), based on the assumption that the percentage of the body weight that is water is 58.0% in males and 47.4 % in females, and that in both sexes, the percentage of water in the blood is 80.65 %. For example, after inserting the slide into the case with the male side up, align 2 on Scale B with Oz. 80 proof spirits on Scale A, and read above 150 lbs. on Scale D, the answer of 0.0381 % , i.e., 0.038 % . If the female side of the slide is used, it will be noted that Scale B is positioned to reflect the lower percentage of body water in females; drinking the same amount of alcohol will result in a higher concentration of alcohol: for a 150 lb. female the concentration in the blood would be 0.047%.
From the Digital Alcohol Studies Archives
- Read more about the Alco-Calculator
- Greenberg, L. A. (1945). Lecture 4: The concentration of alcohol in the blood and its significance with a demonstration of the alcoholmeter. In Alcohol, science and society: Twenty-nine lectures with discussions as given at the Yale Summer School of alcohol studies (pp. 45-58) Quarterly Journal of Studies on Alcohol.
- Greenberg, L. A., Pandina, R. J., & Lester, D. (1983). Instruction Manual for the Alco-Calculator. Rutgers Center of Alcohol Studies.
- Visit the Digital Alcohol Studies Archives