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H G T O W H I C "HYPO" WASTE TO SILVER NITRATE
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thiosuifate "fixer" waste. You ;ne& only some zinc
powder, salt, concentrated nitri.c acid, sodium hydroxide
Dellets. table sugar, filter paper, and'ordinary high
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Heat this to boiling. Anytime while heating you
add the wet sjlver chloride precipitate. A grayish
precipitate of nodules forms immediately.
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ordinary table sugar (sucrose) to the boiling
solution. Frat- takes place each time you add
sugar. Continue adding sugar (could be as many
as 10 times) until frothing ceases. The solution
will then be a clear brownish color. Boil 5-10
minutes more.
out the procedures.
Advise your photography club to save all of their
hypo waste solution. The waste contains silver
compounds dissolved from the developing paper during
processing. Depending upon the activity of the club
you will get about five grams of silver nitrate
crystals per litre of hypo. (There must be a way to
extract pure silver from this too, but I do not know
how. This writer will welcome any short-cuts!)
Decant the brown liquid into the sink and
wash the grayish nodules with distilled water
4-5 times until no brown remains.
Dissolve the gray nodules
acid. Vent the fumes.
Obtain a Generous amount (about 10 L) of hypo waste
solution from the darkroom. For convenience,
treat one litre at a time thus:
Filter the cloudy liquid to get a clear filtrate.
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12 g of&ej
and stir a minute. This will replace the
silver which will settle out as a grayish-black
mud. TeSt for completion of the exchange by
placing a ribbon of shiny m e r m in the
solution. Any silvering of the surface means that
you need to add more powdered zinc per litre.
To each litre of waste add 10
Prepare about 500 mL o f two-mlar sodium hydroxide
and add the clear filtrate to it. An ugly dark
brown precipitate of silver oxide will form. If
this should disappear into solution again upon
stirring, then add more concentrated solution o f
sodium hydroxide until the precipitate remains.
Wash the precipitate a few times. Cap and store
if you desire, otherwise:
When the gray sludae has settled, decant the
silver-free solution+ into the sink as waste.
Save the sludge in a separate beaker. Keep the
sludge in the beaker moist.
To the total supply of grayish-black mud, carefully
add small amounts of concentrattd_ r i i G a ~ .
Good ventilation (use the hood) is required to vent
the toxic gases emitted in this step. Continue
to add acid until all effervescence stops. You
may need to add some distilled water in case the
heat generated turns the mud into lava-like
consistency. Then add more water for convenience
in the next step.
(5) Filter this liquid through an ordinary filter
paper. The filtrate. containing the silver as
silver nitrate, will be a light yellow solution.
(6) Pour concentrated m*
chloride solution- into
the filtrate to form a heavy white pmcipitate
of silver chloride. Wash this with distilled
water a few times, decanting the waste liquid,
and leaving the white precipitate.
(7)
.. . Obtain a large (1000 mL) beaker and prepare at
least 500 mL-of six-molar sodiurg hydroxid?.
in concentrated nitric
Dissolve the silver oxide in concentrated nitric
acid to give silver nitrate solution. Filter
this solution into suitable containers for
drying.
Dry the silver nitrate in a low-heat oven to
prevent spattering or brownish discoloration.
(15) Scrape out and gently grind the nitrate crystals
in a mortar. Then put the powdered crystals in
a dark bottle for storage.l
*Step
(3) Petersen's Photographic magazine, January
1981 page 1 1 states, "A gallon of fixer can accumulate
from . I to 1.2 troy ounces o f the precious metal
(silver). Additional dollar savings can be gained
because with replenishment, hypo may be reused after
si lver has been extracted."
I just read that today, and although the article has
nothing to do with this procedure, it could mean that
the liquid in step (3) can be saved for the darkroom.
L
HOW LONG IS THE DOUBLING TIME?
In I979 the world population increased by
1.7%
In 1980 ;he cost of living increased about 10%
(in Canada)
For example, world population will double in
70/1.7 = 41 years; the cost of living will double
in 70/IO = 7 years.
We know this means an increase next year, b u t a
quick way to find out the number o f years to double
is to divide 70 by the annual percentage increase.
The arithmetic I leave up to the reader, but this
information was first heard from Reg Clarke of
Queen's University during a lecture given at the
University o f Waterloo in the mid-70's.
4 CHEM 13 NEWSISeptember 7981
(Thanks t o S t u a r t Colt, Merritron High School,
10 Seymour Avenue, St. Catharines ON LZP 1 A 4 1 .