The History of refrigerator was occurred in the 19th century.
The first person who knew the principle of cool is a Scottish man.
He knew by accident that “Ether” is able to make metal cool.
In 1879, the German engineer took “Ammonia” to replace “the old one”.
Fifty years later, the two Swedish engineers developed the refrigerator
that used electric power, and it was used until now.
The refrigerator is cool by using the two principles of science that are :
when liquid evaporates to steam, it will take a temperature from things
that are around itself out too. And in place of low pressure, liquid will
evaporate in the low temperature or in cool. So a matter that is used to cool
should be liquid that evaporate easily in the low temperature