Hi, during the winter months the air gets very dry in our house because of
using the central heating.
to make the air more moist we have been using a small humidifier, the type
that you put water in, and it puts a stream of cold mist into the air.
we have been using tap water in the humidifier and it seems to lay a white
dust on everthing nearby.
presumably that is the chalk in the tap water? (being in london u.k. the tap
water is quite hard [i.e. chalky].
is there a way to stop this dust. many thanks
Whoa. There are some errors here.
Your "white powder" is mostly lime (Calcium oxide or CaO) and lime
compounds like calcium carbonate.
A filter will not filter out dissolved lime unless an expensive
reverse osmosis filter is used. Depending on the type, the other
filters filter out suspended particles, use redox to convert some
contaminates into hydroxides, or in the case of carbon filters, absorb
volatiles that have more affinity to the carbon than the water.
Adding vinegar (CH3COOH) to water will not remove the lime. It will
reduce the hardness or "sweeten" it by making more calcium carbonate
(CaCO3) and adding acid, but when the water is all evaporated, the
white residue will still be there.
Adding salt to distilled water in a "cold" humidifier won't help. A
"cold" humidifier sprays the water, often in microscopicly small
droplets created by cavitation from an ultrasonic vibration, whereas a
"vaporizer" used to help people with colds uses electrodes immersed in
water to heat and boil the water. Adding salt there increases the
current flow and heating ability.
A "cold" humidifier can be a breeding ground for germs, which it then
sends into the air. The effect is worsened when the water is not
changed out regularly and the container cleaned. Because of the heat
and method of evaporation, vaporizers avoid this, but can suffer more
The short answer is to use distilled water, reverse osmosis filtered
water, or rain water in a "cold" or ultrasonic humidifier.
I'm going by experience with the vinegar from few sources. I know it
works to prevent any white film on canning jars when processing them.
If you don't add vinegar, there is a white film on the jars. I've used
vinegar for removing water deposits in my dishwasher. Both these
applications work well but they envolve heat. When we had a table top
humidifier, I used vinegar in the water to prevent water deposits in the
humidifier. This reduced the white dust on the funiture from the
humidifier. I'm not sure why it worked, just that it did <shrug>
It is possible that the vinegar formed large percipitate particles of
some of the calcium compounds that then sunk to the bottom of the tank
without attaching to it. A lot would depend on the exact chemistry
and contamination of the water.
On Tue, 22 Mar 2005 23:53:22 GMT, email@example.com wrote:
Thanks for a very interesting post. My chemistry isn't good enough to
have written it [without refreshing my memory + Excedrin], but I could
keep up with most of it. (Redox conversion to hydroxides!? Oh, No!) LOL
Water chemistry is never dull.
School - Four walls with tomorrow inside.
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