James Osbourne, Holmes wrote:
> Hi Marshall,
>
> Is there a reference that details the procedure?
> I would like to try it to see what happens.
>
> James Osbourne Holmes
> [email protected]
>
> -----Original Message-----
> From: Marshall Dudley [SMTP:[email protected]]
> Sent: Friday, November 12, 1999 10:47 PM
> To: [email protected]
> Subject: Re: CS>wet chem
>
> James Osbourne, Holmes wrote:
>
> > Hi Marshall,
> >
> > Bruce Marx and a tech rep from Hach had different results with that
> > process. Digestion produced wildly unreliable results. The process done
> > without was consistently y accurate. I do not know what analysis they used
> > to verify this.
>
> The digestion that Bruce had poor results with is using the Hach digestall, a
> very expensive piece of equipment that Hack talked him into buying, and then
> had to take back. It is known that this equipment produces bad results. The
> digestion I am talking about is nothing more than dissolving the silver in
> boiling nitric acid, then neutralizing with Sodium Hydroxide to produce silver
> nitrate.
>
> Marshall
This is the method given to me by Hach after going back and forth a few time,
and
the one I am using:
Sorry for the oversight on the HCl digestion method. We do have a silver
digestion method using only nitric acid.
The procedure to do a digestion of a silver sample is as follows.
1) Transfer 50 ml of sample to 150 ml beaker and add 2 ml of conc. Nitric
Acid
2) Place beaker on hot plate and cautiously evaporate to dryness
3) Cool the beaker and then add another 2 ml of Nitric Acid. Cover the
beaker
with a watch glass and return to hot plate.
4) Continue heating with gentle refluxing to near dryness.
5) Cool the beaker then add 2.5 ml of 1:1 Nitric Acid. Warm the beaker to
dissolve any residue from the evaporation steps.
6) Wash down beaker walls and watch glass with demineralized water. Filter
the sample through filter paper into a 50 ml volumetric flask. (If
thiosulfate
is present in sample see note)
7) Add 2 drops each of Phenolphthalein Indicator and Thymolphthalein
Indicator solution. Add Sodium Hydroxide until soultion is pink in
color.
A purple color indicates pH of 10. If this is the case add one drop
of 1:1
Nitric Acid then 2 drops each of the indicator solutions. Repeat the
addition of the Sodium Hydoxide to the pink color.
NOTE: If thiosulfate is present, add 4 ml of 50% Hydrogen Peroxide in
place of the concentrated Nitric acid in step 1. Continue with steps 2
through 8. (Taken from DR100 for Silver Instrument Manual)
Technical Support Specialist
Hach Company
P.O. Box 389
Loveland, CO 80539
Phone in the U.S.A.: 800-227-4224
Phone International: 970-669-3050
FAX: 970-669-2932
E-Mail: [email protected]
www.hach.com
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