Hot Breath of Cold Guinea Pigs

In 1780, two men in France experimented with a guinea pig: Antoine Lavoisier, an amateur scientist, and Pierre-Simon Laplace, an academic mathematician.

Lavoisier started by inventing a calorimeter, a device that measured calories of heat produced by an experimental subject, in this case an unfortunate guinea pig.

The calorimeter was essentially a bucket inside a bucket inside a bucket. The central bucket held the guinea pig. The next bucket was filled with ice. The outside bucket was filled with snow. The snow kept the outside wall of the ice bucket at a constant temperature. The presence, and breathing, of the confused creature heated the ice, which melted. This went on for 24 hours. They collected 370 grams of melted ice water during that time.

Lavoisier and Laplace concluded that the total heat produced by the furry little mammal equaled the amount of heat required to melt that amount of ice.

A key requirement for success in the experiment was that the guinea pig was alive and breathing, because respiration was the topic they were investigating. They knew that respiration was similar to combustion: air goes in, changed air (with carbon dioxide) came out, and heat was produced.

The proof that respiration was similar to combustion was in the water they collected. It was not just water. It was acidic due to the presence of carbon, which could only have come from the lungs of the carbon-based life-form, the harmless guinea pig.

They concluded, "Respiration is thus a very slow combustion phenomenon."

It was an original theory about biochemical conservation of energy. They had good reason to be proud of themselves.

Fourteen years later, however, their fates headed in very different directions. Lavoisier had unfortunately held a longtime job as a tax collector. This made him unpopular among the people who seized control of Paris during the French Revolution, and who were overzealous in their use of the guillotine. Laplace stayed away from the city and accepted a job working for the new government by calculating the trajectories of cannon balls.

Follow-up question and answer:

Question: Why a guinea pig?

Answer: Though native to Peru, guinea pigs had been pets of wealthy Europeans for more than a century. Lavoisier, who was wealthy, would logically have chosen a small compliant pet to drop into the ice-cold bucket. An alternative could have been a kitten, but that might have been met with razor-sharp objections.