For thousands of years, people used ice to chill food and drink. But by the end of the 19th century, sewage pollution of rivers and ponds made untainted ice hard to find. It had long been known that when a liquid evaporated, it absorbed heat from its surroundings.
In 1748, William Cullen demonstrated at Glasgow University that artificial refrigeration was feasible by letting ether boil into a vacuum. But it was an American physician, John Gorrie, who in 1842 built a device that cooled hospital fever wards by compressing a gas and then allowing it to expand.
Gorrie went on to develop ice-making machines, and so the fridge was born.
Unfortunately, gases used in early systems - ammonia, sulphur dioxide and methyl chloride - were highly toxic. So many deaths were caused by leaky refrigerators in the 1920s that people were afraid to have them in the house. And so the search began for an alternative. Three companies - General Motors, Frigidaire and DuPont - collaborated, and in 1928 a scientist named Thomas Midgley Jr came up with a new organic compound, a chlorofluorocarbon (CFC) called Freon. To prove it was non-toxic, Midgley publicly inhaled a lungful of the vapour. It was also non-flammable, and to prove this, he exhaled the vapour into a candle flame.
Almost overnight, CFCs transformed refrigeration. Production of fridges, freezers and air conditioners boomed, and industry came to rely on the process. Then, in 1974, scientists warned that CFCs migrating to the upper atmosphere could damage the earth's protective mantle of ozone. In 1985, an "ozone hole" was discovered, and it became apparent that Freon had been far from harmless after all.
Midgley's other bright ideas, apart from finding a way of adding salt to otherwise wholesome popcorn, included leaded petrol. This work gave him lead poisoning, a fact he kept secret. But it was his final invention that killed him. At 51, Midgley contracted polio and lost the use of his legs.
He invented a harness to get himself out of bed and, on November 2, 1944, became entangled in the straps and was strangled.