From: Yu rei (nanocrystals2003@yahoo.co.jp)
Date: 07/02/03-06:13:47 AM Z
Sil, Ryuji...
You both supplied a wealth of information. Thank you.
My question was sparked by the observation that anhydrous
sodium carbonate was less expensive than the decahydrate,
if one allowed for the weight of the water.
Since normally, if the weights of the non-aqueous part is
equilized, substances containing differing amounts of
water of crystalization, can be used interchangeably.... I
thought I should be buying the anhydrous form.
The problem was that I could find no evidence that any
other form of sodium carbonate besides the decahydrate
could and had indeed been used as "Washing Soda"
Was there a perhaps reason ?
I had thought someone on the list could just go to their
washing machine and pick up a box of "Washing Soda" and
let us know what it said.
No one did, however, so I wrote ARM & HAMMER.
For all who care, here is their answer:
Thank you for contacting us recently. Our ARM & HAMMER
ョ Super Washing Soda contains anhydrous sodium carbonate.
We hope this information is helpful.
Well, unless someone on the list NOW reads the lable amd
tells us something different is on the box or in some lab
report somewhere, I think we have closure on this.
It makes sense, too, since it is cheaper and allows
smaller packaging and smaller useage amounts.
The differing amounts of water determined by Ryuji and
mentioned by Sil, can possibly be attributed to the
anhydrous material picking up some water somewhere along
the way.
Ray
> From: Sil Horwitz <silh@earthlink.net>
> Subject: Re: Sodium carbonate "Washing soda"
> Date: Mon, 30 Jun 2003 10:23:52 -0400
>
> > "Washing Soda" has indeterminate amounts of H20.
> As manufactured, it is a
> > mixture of all three forms, mostly the
> decahydrate, but during storage it
> > loses some of the water, and the monohydrate is
> the stable form.
>
> I wonder if you are talking about general term
> washing soda, not the
> Arm & Hammer Washing Soda product. I did assay about
> two years ago,
> and at that time, it was sodium carbonate
> monohydrate. Two methods I
> used were measurement of loss of weight at 250+C in
> crucible furnace
> and that of total alkalinity through titration.
>
> The following information is based on a fairly
> detailed article by
> Christian Thieme, Solvay Alkali GmbH, Solingen,
> Germany.
>
> Commercial sodium carbonate monohydrate technical
> grade comes in
> several physical forms, "light ash," "dense ash,"
> "granulated," etc.,
> varying in bulk density and appearance. These come
> as a mixture of
> different particle sizes, but in these cases the
> powders do not
> necessarily mean that they contain any less water,
> unlike less stable
> decahydrate case.
>
> > As noted above, as manufactured
> > (non-purified for laboratory use), the decahydrate
> is the product. Other
> > forms are produced by further processing
> (desiccating or heating).
>
> In my understanding, crude sodium carbonate is
> extracted from Solvay
> or modified Solvay method plants after calcining
> sodium bicarbonate.
> Therefore, the crude sodium carbonate should be
> mostly anhydrous form,
> from which variety of monohydrate forms like "light
> ash" are produced
> and shipped. (This crude stock is already
> comparable to technical
> grade in terms of its purity.)
>
> The decahydrated form is made from the crude stock
> by dissolving it in
> water, then bring the solution to crystal
> precipitation. In order to
> make hard crystals, some sodium sulfate needs to be
> present. Even
> after crystallization, the mole ratio of sodium
> carbonate to sulfate
> impurity is much higher in decahydrate form.
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