Date: Wed, 29 Dec 1999 17:46:53 -0500 (EST) From: "Carl Strohmenger (HSC)" <cstrohme@com1.med.usf.edu> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg4273$foo@default> Subject: Re: water
On Wed, 29 Dec 1999, Dave Evans wrote:
> Dear Carl,
>
> > Actually, the boiling method removes *suspended* solids, not dissolved
> > minerals. In general, boiling will increase the amount of dissolved
> > material since most salts are *more* soluble in hot water than in cold
> > water - so boiling the water brings the solution closer to saturation
> after
> > subsequent cooling.
> > The suspended solids can be removed by pouring off the cooled water after
> > boiling, and of course, any dissolved gasses (eg chlorine) tend to be
> > driven out of the solution during boiling, too.
>
> What about CaCO3 in the water? If you boil the water, will not the CO2
> be driven off leaving Ca(OH)2 (isn't it less soluble than carbonate?) to
> preciptate out?
>
> Dave Evans
>
You raise an interesting question. It might seem that this would
happen, but the increase in temperature will not have much effect on the
equilibrium point of the reaction. Adding acid or base to the water would
push this reaction away from the equilibrium point much more effectively.
You can have suspended solids in water if the particle size is very
small - so small that the normal motion of water molecules is enough to
keep them from settling out of the liquid. When you boil the water, these
suspended particles can start to clump together (ie become larger
particles) and eventually be large enough to settle out.
Also, you can have a reaction involving other salts in solution, such as
sodium chloride, potassium nitrate, etc with the calcium carbonate or
magnesium salts and wind up with CaO or MgO.H2O precipitating out. In
either event, though, you still have dissolved salts (sodium or potassium
or other salts) remaining and they will build up in your soil as the water
is used by the plant or evaporates to leave the salty residue behind.
Generally, sodium and potassium salts are much more soluble than
magnesium and calcium salts. Also, nitrates and chlorides are likely to be
more soluble than oxides.
To get pure water, you need to remove all the mineral salts - and
that means distillation or RO treatment.
Also, different species will have different tolerances for salty
water and chlorine. But in the end, purer water is better for our plants.
Water chemistry is an old science, but is probably not entirely
understood yet.
- Carl
This archive was generated by hypermail 2b30 : Tue Jan 02 2001 - 17:32:09 PST