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Re: Freezing Indian pumps

Freezing point depression is one of the colligative properties... which
means it's dependent only on the number of particles in the solution, and
not the type of particle -- which means you can get by with the lowest
concentrations of something that ionizes when it dissolves (like salt),
and you'll need more of a big molecule than a small one.

The cheapie things I could think of for this problem would be
salt (NaCl-- slightly toxic at some levels on some plants)
potassium nitrate (fertilizer component; you may not want to alter 
         nutrient cycles)
ethanol and methanol (hard to come by cheaply; methanol is more toxic
         than ethanol)
sucrose (table sugar) non-toxic, may char, probably will stink a bit

Propylene and etheylene glycols have also been suggested, as they're in
commercial antifreezes.  Both are fairly toxic, though propylene glycol
is less toxic to most mammals; they're about equally toxic in aquatic
systems, as I understand it.

I'd suggest using hard water, since you've got free ions in there already,
and supplementing with a little sugar if you need to.

Kay Lancaster  kay@fern.com



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