Yes Sulphur Dioxide stinks,is toxic-but is a good and EFFICIENT refrigerant.-And it was inexpensive.Ammonia is a good refrigerant,too it is toxic-but VERY effective esp for very low below freezing applications-Ice cream makers still like it.Ice houses that made block ice-still traces of them today-liked ammonia.It was used along with brine.The ammonia evaporator coils were used in the brine-the container of what you wanted to freeze was put in the brine.This gave isolation in case of ammonia leaks.Esp for food or ice to be used with food refrigeration.Of course toxic refrigerants CANNOT be used for human comfort refrigeration directly becuase of their toxicity.Food contamination with the older Sulphur Dioxide fridges was rare-but leaks were serious-when sulphur dioxide contacts air-turns to sulphuric acid vapor-TOXIC-burns lungs,eye,skin.and reaction of it with some materials could cause a fire or explosion.