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BAC Tools

Estimating alcohol concentration

The first person to measure alcohol concentration from body fluids was Erik M. P. Widmark, a Swedish chemist, in 1914. While the “Widmark Micromethod” spread through much of Europe in the 1920s and 1930s and became an established forensic test,the United States still relied exclusively on behavioral evidence

Alcometer

The Alcometer, developed by Leon Greenberg at Yale in the in 1941, marked a significant advancement from Widmark's theoretical calculations to practical blood alcohol measurement. The portable breath-testing device was one of three “first-generation” breath-alcohol analysis devices that were introduced at the time, along with the Drunkometer and the Intoximeter. Unfortunately for Greenberg, the Drunkometer, invented in 1931 by Indiana University’s Rolla N. Harger, lays claim to the first breath-test instrument used in the field by police. 

The Alcometer, sometimes also called Alcoholometer, worked by mixing the alveolar air in one’s deep breath with iodine pentoxide. If there was alcohol in one’s system, the reaction released iodine, which, when absorbed in a starch solution, caused its color to change in proportion to the amount of alcohol present. The device complemented Widmark's formula by providing real-time measurements rather than theoretical calculations. Results obtained from the Alcolometer showed a high correlation with direct blood analysis.

A breakthrough, the Alcometer, and its two close competitors were used for a very long. time, replaced by the Breathalyzer, which was introduced in 1954.  Nevertheless, the Alcometer was an important predecessor to modern breathalyzers and helped establish the scientific basis for breath alcohol testing in law enforcement and research. Greenberg's work also helped validate the relationship between breath and blood alcohol levels.

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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.
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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.
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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.
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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.

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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. 
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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.
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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