Yesterday Robbie asked:

>[ Ammonia is still used in commercial freezer plants; I wonder
>[ why sulfur dioxide (SO2) was favored in smaller refrigerators?

Prior to the invention of Freon in the late thirties, SO2 was usually
used in small refrigerators because liquefied NH3 (ammonia) gas is very
hazardous, as opposed to the liquid ammonia NH3OH (ammonia water) we
are familiar with.

If it gets on the skin, or is breathed, it causes terrible burns by
leeching out the H2 and O2 from organic material.  Also, it can break
down and burn in certain circumstances.  SO2 only stinks if it leaks
out.

NH3 is still the best refrigerant, but it is impractical for small,
isolated units.  In large installations, the chiller unit is usually in
a safe, isolated area.  The liquefied gas is evaporated in a heat
exchanger, which cools a brine that is piped to the various cold rooms,
ice machines, or freezers throughout the plant.

Richard Vance