When Thermometers Were Filled With Brandy, Not Mercury

Picture a scientist in the 1600s checking the temperature—not with a sleek mercury thermometer, but with a glass tube filled with brandy. Before mercury became the go-to liquid for measuring heat, early thermometers relied on alcohol, including wine and spirits, to track temperature changes.

The first sealed alcohol thermometers emerged in the mid-1600s, with Ferdinando II de' Medici, Grand Duke of Tuscany, creating modern-style thermometers in 1654 using alcohol in glass tubes with bulbs and stems. Even earlier, in 1629, Joseph Solomon Delmedigo documented an accurate sealed-glass thermometer that used brandy in his work "Ma'yan Ganim (A Fountain of Gardens)."

Why Brandy Made Sense

Alcohol wasn't just a random choice—it had practical advantages. Liquids expand when heated and contract when cooled, making them perfect for temperature measurement. Alcohol is more sensitive to temperature changes than mercury, meaning it showed smaller temperature variations more clearly. Plus, it doesn't freeze at normal winter temperatures like water does, making it reliable year-round.

The Florentine scientists actually experimented with mercury but chose alcohol instead because of its superior sensitivity. Brandy and other spirits were readily available, didn't corrode glass, and remained liquid across a useful temperature range.

The Switch to Mercury

So why did we abandon booze-filled thermometers? Mercury's wider liquid-state temperature range made it more versatile. While alcohol thermometers worked well for everyday temperatures, mercury could measure much hotter and colder extremes without boiling or freezing.

The turning point came in the early 1700s. Daniel Gabriel Fahrenheit made his first alcohol thermometer in 1709, but by 1714 he'd created his first reliable mercury thermometer. Mercury's consistency and broader range made it the new standard for scientific measurement.

Still, alcohol thermometers didn't disappear entirely. They're still used today in situations where mercury's toxicity is a concern, like in household thermometers and some scientific applications. The liquid inside modern alcohol thermometers is usually dyed red for visibility—a far cry from the amber brandy of the 1600s, but the same basic principle.

The Bigger Picture

Those brandy-filled tubes represent more than just quirky history. They were part of the Scientific Revolution, when inventors were figuring out how to measure the invisible—temperature, pressure, time. Before standardized thermometers, "hot" and "cold" were subjective. These early devices, whether filled with brandy or mercury, gave scientists a common language.

Next time you check a thermometer, remember: for decades, the best way to measure a fever or the weather involved a glass tube of spirits. Science has always been about using whatever works—even if that means your lab equipment doubles as a cocktail ingredient.