It's a very clever trick. A refrigerator without a compressor which uses heat as the energy source. It could run on either a gas flame, or an electric heating element. There are three working fluids (butane, water and ammonia) and it works without a compressor by using differences in partial pressure. That is, the pressure of each component in a mixture, and changing the composition of the mixture rather than using a compressor. It basically works by adding and removing ammonia at different points to cause the butane refrigerant to evaporate and condense in the appropriate places. Water is used to remove the ammonia (absorption) from the gas mixture in the condenser side (which, because the total pressure is about the same everywhere, increases the partial pressure of butane causing it to condense and therefore reject heat). On the evaporator side, ammonia (gas) is added again to lower the butane partial pressure and cause it to evaporate (the cooling effect). The other part is to separate the water from the ammonia again, that's the part where you add heat and what ultimately drives the process.
> The three working fluids in this design are water, ammonia, and butane. [1] The Einstein refrigerator (co-invented with Leó Szilárd) was actually a modification of an earlier three-fluid absorption design created by Swedish engineers Baltzar von Platen and Carl Munters
Einstein–Szilard refrigerator: https://en.wikipedia.org/wiki/Einstein_refrigerator :
> The three working fluids in this design are water, ammonia, and butane. [1] The Einstein refrigerator (co-invented with Leó Szilárd) was actually a modification of an earlier three-fluid absorption design created by Swedish engineers Baltzar von Platen and Carl Munters