It was based on an absorption cycle instead of the compression cycle used with modern refrigerants. Ammonia was evaporated to provide the cooling, then absorbed by water and driven back into vapor by heating, then condensed and evaporated again. It was relatively inefficient, but was usually driven by waste heat from an industrial boiler, so a ship was a natural for it.
Fishing ships still use ammonia based refrigeration.
Thanks for that explanation. The 19th century was a great time for interesting inventions. The scale of things hadn’t gone nano yet so everything was very physical and had a great sculpural quality. Even electronic gizmos were interesting with their big coils and physical throw switches and stuff. I’ll bet one of these Victorian refrigeration systems would be fascinating to look at. Probably a total Rube Goldberg maze of tubing and valves and pressure meters — with lots of polished brass. It would be totally steam punk.
Read about British colonials in the So. Pac islands using similar to make ice. Forget the name but would have been circa [very] early 1900s.