Science & Technology

How was the Nature of Heat Unravelled?

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Heat comes from friction, not from some internal chemical prop­erty of each substance. Count Rumford discovered it in 1790, informs Prof Ashoka. A Different Truths exclusive.  

Scientists believed that heat was an invisible, weightless liquid called caloric. Things that were hot were stuffed with caloric. Caloric flowed from hot to cold. They also believed that fire (combustion) came from another invisible substance called phlogiston, the vital essence of combustible substances. As a substance burned, it lost phlogiston to air. The fire ended when all phlogiston had been lost.

Erroneous beliefs kept scientists from understanding the nature of heat and of oxidation (including combustion) and stalled much of the physical sciences.

These erroneous beliefs kept scientists from understanding the nature of heat and of oxidation (including combustion) and stalled much of the physical sciences. Benjamin Thompson, who called himself Count Rumford, shattered these myths and discovered the principle of friction. This discovery opened the door to a true understanding of the nature of heat.

How Was It Discovered?

In 1790, 37-year-old Count Rumford was serving the King of Bavaria as a military advisorAs part of his duties, he was in charge of the king’s cannon manufacturing.

Born in Massachusetts as Benjamin Thompson, Rumford had served as a British spy during the American Revolutionary War.

Born in Massachusetts as Benjamin Thompson, Rumford had served as a British spy during the American Revolutionary War. Then he spied on the British for the Prussians. In 1790, he fled to Bavaria and changed his name to Count Rumford.

The cannon manufacturing plant was a deafeningly noisy warehouse. On one side, metal wheel rims and mounting brackets were hammered into shape around wooden wheels and cannon carriages. Steam rose from hissing vats as glowing metal plates were cooled in slimy water.

On the other side of the warehouse, great cannons were forged. Molten metal poured into huge molds — many 12 feet long and over 4 feet across. Spinning drills scraped and gouged out the inside of each cannon barrel.

Drill bits grew dangerously hot. Streams of water kept them from melting.

Drill bits grew dangerously hot. Streams of water kept them from melting. Hissing steam billowed out of the cannon barrels toward the ceiling, where it condensed and dripped like rain onto the workers below.

On one visit, Rumford recognised that great quantities of heat flowed into the air and water from those cannon barrels. At that time scientists believed that, as a substance grew hotter, more caloric squeezed into it. Eventually, caloric overflowed and spilled out in all di­rections to heat whatever it touched.

Rumford wondered how so much caloric (heat) could pour out of the metal of one can­non barrel

Rumford wondered how so much caloric (heat) could pour out of the metal of one can­non barrel — especially since the cannon barrels felt cold when the drilling started.

Rumford decided to find out how much caloric was in each barrel and where that calo­ric was stored. He fashioned a long trough to catch all the water pouring out of a cannon bar­rel while it was being drilled so he could measure its increase in temperature.

Rumford didn’t want any caloric escaping as steam he couldn’t capture and measure.

He also directed that extra hoses be sprayed on the drilling to prevent the formation of steam. Rumford didn’t want any caloric escaping as steam he couldn’t capture and measure.

Drilling began with a great screeching. Hoses sprayed water onto the drill bits. The metal began to glow. A torrent of heated water eight inches deep tumbled down the narrow, foot-wide trough and past the Count and his thermometers.

More caloric flowed out of that cannon barrel than he could have imagined in even his wildest dreams.

Rumford was thrilled. More caloric flowed out of that cannon barrel than he could have imagined in even his wildest dreams. And still, the hot water continued to flow past him, all of it heated to more than 50 degrees Celsius.

Eventually, the Count’s face soured. Something was very wrong. The metal cannon barrel had already lost more than enough heat (caloric) to turn it into a bubbling pool of liq­uid metal many thousands of degrees hot. It seemed impossible for so much caloric to have existed in the metal.

Count Rumford watched the borers go back to work and realised that what he saw was motion.

Count Rumford watched the borers go back to work and realised that what he saw was motion. As drill bits ground against the cannon’s metal, their motion as they crashed against the surface of the metal must create heat. Movement was being converted into heat.

Today we call it friction and know it is one of the primary sources of heat. But in 1790, no one believed Count Rumford’s new theory of friction heat, and they held onto the notion of caloric for another 50 years.

Fun Facts

Friction with air molecules is what burns up meteors as they plunge into the atmosphere.

Friction with air molecules is what burns up meteors as they plunge into the atmosphere. That same friction forced NASA to line the bottom of every space shuttle with hundreds of heat-resistant ceramic tiles. Failure of one of those tiles led to the explosion of the Columbia in 2004.

Photos from the Internet


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