In 2018, ice is everywhere. You can make it yourself by putting a tray of water into the freezer. Or you can find one of those special fridges with an in-unit ice machine and wait for the cold stuff to simply plop out into your cup. But ice used to be much, much harder to get your hands on--and in the era before A/C, it was desperately desired. That's why, for much of the 19th century and into the 20th, ice was the cold, hard heart of an international economy called the "frozen water trade."