> Gunpowder...is only humanity’s second great experiment (after fire) with harnessing chemical energy is this true? how about adding salt to ice to make it col

> Gunpowder...is only humanity’s second great experiment (after fire) with harnessing chemical energy is this true? how about adding salt to ice to make it colder? fermentation creates heat, was it ever scavenged for anything? Just curious but it seems like there might have been some other thermic chemistry over the years.