This is the initial story in our LSA and the Bicentennial series, which will feature tales from the College that complement the University's year-long recognition of its first 200 years. Look for more stories in the series throughout 2017.


Around the time that Prohibition ended—on December 5, 1933—few people were making New Year’s resolutions to lay off the alcohol.

The first six months of 1934 saw huge spikes in drunk-driving accidents. Alcohol-related deaths on the road quadrupled in Chicago alone. And fending off the public hazard was tricky for the cops. They could pull over an erratically weaving car, but had to rely on ballpark estimates for whether a person was too drunk to drive. Police officers tested drivers with tongue twisters like “Methodist Episcopal,” walking a straight line, picking up small objects from the ground, and standing steady with eyes closed. They checked for dilated pupils and smelled a driver’s breath for alcohol. But these tests hardly counted as conclusive evidence that could stand up in court, and DUI laws remained tough to enforce. An estimated 50 percent of car accidents at the time involved a drunk driver. These desperate, drunken times begged for a solution.

Enter William Duncan McNally (A.B. 1905). As chief chemist in Chicago’s Cook County Coroner’s Office and a member of the Rush Medical College faculty, he knew a lot about how to test human bodies for the presence of foreign chemicals. He insisted that alcohol intoxication should be measured and quantified, not just eyeballed, and came up with a way to do it.

Welcome to the world, breath analyzer.


McNally's breath analyzer not only could help convict drunk drivers pulled over by the police, but also clear the record of any driver who'd been falsely accused. (Left) image from Popular Science Monthly magazine (1927); (right) image from William Duncan McNally, Toxicology (1937)


Crash Course

McNally created one of the first breath analyzers in 1927, based on methods he’d been using for years in the coroner’s laboratory. (The proprietary term “Breathalyzer” came later, with the invention of a more portable device.) The general idea behind McNally’s invention was this: Subject blows into a tube. The breath moves through a special chemical mixture in a vial. If the breath carries more than a certain concentration of alcohol, the liquid in the vial changes color from orange to green.

Chemistry nerds may know this reaction as the oxidation of ethyl alcohol to acetic acid. In a solution that holds potassium dichromate, the alcohol in a subject’s breath loses electrons, and those electrons transfer to the potassium dichromate. The chemical reaction converts orange potassium dichromate into green chromium ions dissolved in solution.

Popular Science Monthly magazine flippantly suggested that McNally’s device would allow a nagging wife to test her husband before allowing him to stumble in late. Really, though—preventing abuse by alcoholic husbands was one reason women had agitated for Prohibition in the first place.

And McNally’s own motivations for creating the device really did come out of serving the public. He developed toxicology methods to investigate suspicious deaths, poisonings, and suicides. When McNally noticed an increase in deaths due to carbon monoxide inhalation, he advised homeowners to add ventilation in their garages. He came down hard against the common practice of fumigating urban buildings with hydrogen cyanide, especially after the extremely toxic gas killed not just cockroaches, but also human residents. He suggested that bottles storing poisonous pills should have a peculiar shape—identifiable by both sight and by touch in the dark. And he spoke out against the illegal use of diluted wood alcohol as a cheap substitute during Prohibition, citing tragic cases of blindness and death.


The breath analyzer that caught on early with police squads–a device called the drunkometer–used the same chemical reaction as in McNally's invention. The drunkometer, however, tested a consistent volume of gas by collecting the amount of breath that filled an attached balloon. Image via the Indiana Legal Archive, licensed under CC BY-SA 4.0


Safety in Numbers

McNally’s breath analyzer was a precursor to later versions that police came to depend on. Police first hit the streets with drunkometers (yes, drunkometers) in the late 1930s. The devices exploited the same chemistry as McNally’s contraption, except subjects exhaled into a balloon. In the first court case to make use of such evidence, the lawyer defending a drunk driver scoffed at the silly “balloon test,” arguing that he’d blown the test as a demo in the courtroom and passed for sober—despite having drunk three cognacs and a glass of beer during lunch. The judge ended up exonerating the driver. But over time, breath analyzers have grown more and more accurate.

The trademarked Breathalyzer showed up in 1954. Its inventor analyzed traffic data from Grand Rapids, Michigan, in 1964 and showed that impaired driving increased wildly when blood alcohol concentration reached 0.08. His work led to the contemporary legal limit that most state laws follow.

Today, breath analyzers are common and inexpensive enough to buy in drug stores, install on the wall at a pub, and use with an app on a cell phone. Be careful out there. Use the tools, and know that one LSA alumnus applied chemistry and hard work not just to punish tipsy drivers, but to help keep roads safe for everyone.



Other stories in the series:


Top image courtesy of the USC Libraries Special Collections