Per low-cost, "sustainable" refrigeration, these things have been around since the 20s. They work - And continue to work. There's not much to go wrong, given reasonable care - Fuel is anything that burns... http://en.wikipedia.org/wiki/Icy_Ball http://crosleyautoclub.com/IcyBall/crosley_icyball.html Note the link to modern examples at the bottom of the page. The hardest part of the exercise is getting good data on the thermodynamic properties of NH3/H2O mixtures. When I went looking 20+ years ago, the American Gas Association's Institute of Gas Technology, Research Bulletin # 34, "Physical And Thermodynamic Properties of Ammonia-Water Mixtures", was exactly what was needed. Hopefully still in print, or available on line. If tempted to build one, pl= ease note you do need to understand the engineering detail building, so you end up with a refrigerator, not a bomb - No kidding... Jack --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .