Science & Technology

This 1927 Experiment to Prove Pitch Is a Liquid Is Still Going On

How long would you wait to prove a point? A year? Eight years? 90? Well, depending on what you're trying to prove, you might have to be in it for the long haul. An experiment to show that the tar-like substance pitch was a liquid began in 1927, and it's still going on.

Picture of the Pitch Drop Experiment taken two years into the life of the 8th drop.

Pitch Perfect

Pitch isn't in our everyday lexicon these days, but it's been a part of human history for a long, long time. We used to use it to seal up the cracks in sailing ships, and we still use it in roofing and road construction. But back in 1927, an English physicist named Thomas Parnell proposed something that seemed preposterous. Maybe the rugged substance we drive our jalopies on isn't a solid at all, but a very, very, very slow-moving liquid. And thus, the pitch drop experiment began.

The first thing Parnell had to do was melt down some pitch into its inarguably liquid state. He poured that into a small, conical beaker and waited for it to settle. And waited. For three years. At that point, he cut off the pointed tip of the beaker to turn the whole thing into a little glass funnel. And then he waited again — there's a lot of waiting involved in this experiment. After eight years, in 1938, he finally got proof of his hypothesis: the first drip of pitch dropped from the funnel to the glass jar underneath. The next drop dropped in 1947. Parnell died about a year later, but the experiment has kept on going. After all that, the experiment was a rousing success that proved that pitch is a liquid — one that's 230 billion times thicker than water.

A Solid Plan

Since the beginning, there have been a total of nine drips, and the tenth is expected to fall sometime around 2028. But until 2014, nobody had ever actually seen a drip drop. It just always seemed to happen when nobody was around. But in the year 2000, researchers set up a live-streaming webcam to ensure that the eighth drop onward would be captured — and they failed. Technical issues struck at exactly the wrong time, and the eighth drop was missed as well.

That might be enough to convince you that the whole thing is a fraud. How do we know that there isn't somebody surreptitiously sneaking pitch from the funnel to the jar? That question was finally settled when a drop dropped on camera in 2014 during a beaker change. Because of the unusual circumstances of the drip, the next one is a little delayed. It's estimated to be coming sometime around 2028. Until then, we'll just keep our eyes on the live stream and keep practicing our resting pitch face.

The Pitch Drop Experiment

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Written by Reuben Westmaas February 7, 2018