Giant blocks of ice to refrigeration
Ice blocks were literally cut out of lakes in the north and shipped to the south. The ice trade was a wonderful confluence of new uses for things that were deemed “waste” in the eyes of industry - empty ships traveling back to the south after they’d delivered their goods up to the north (the main direction of trade at the time was south to north), and sawdust (which was used for insulation). Giant ice blocks take a very long time to melt. Even moreso when insulted with sawdust, which kept the ice off the thermally-conductive metal on the floor of the cargo ships.
Ice blocks were being used to break the fever of malaria patients in a hospital in the south. When hurricanes destroyed the ice shipments, a doctor lost a lot of his patients. He sat out to make his own ice, and wound up eventually discovering and inventing the process of refrigeration. Unfortunately, he never really marketed his machine-made ice very effectively and died without having seen the success of his invention.