Ammonia doesn't seem to work well in small refrigeration systems
because it would need to be more "pure", which would have disastrous
effects if a leak should occur, and would seem to be on the prohibitive
list even then.  Sulphur Dioxide was used but was still dangerous if
inhaled because it would "hydrate" in your lungs causing sulphuric acid
to form.  (Bad news!)

Julian Burke