> Gary Auerbach. Says:
>
> >I will keep that in mind next time I am in the woods. Speaking more
> >practically regarding enviornmental impact, I am convinced that
> >platinum/palladium printing using thin papers, EDTA and distilled water
> >to clear is a most non toxic process.
>
> These things can never be stated as absolutes but my studies do indicate
> that platinum printing is one of the more benign alt-photo process. I
> welcome the "real" chemists here jumping in as my training is all practical,
> no academic credentials to lean on.
>
> Points:
>
> Pt and pd are noble metals. They like being in their pure metalic elemental
> states. They are found in nature almost always in that state, not as oxides
> or sulfides etc. Take 500 ml of potassium chloroplatinite and dump it into a
> stream. (Now there is an picture for you!) Fish die. But soon the K2PtCl4
> will run into natural chemicals that quickly cause it to return to its
> metallic state. Pt and pd metal fall to the bottom of the stream as black
> sand where it could be panned out like gold. It's inert and harmless. (I've
> been told by serious hobby gold panners that the beginners on rare
> occassions get a pan full of black powder and dump it not knowing it's
> worth.) After the metal drops out, we have a tiny amount of chlorine gas and
> some potassium chloride, which is sold as a salt substitute for people with
> heart problems.
>
> Oxalates. The stuff that makes spinach bitter. According to the book, "The
> Dose Makes the Poison" there is a lethal amount of oxalaic acid in 10 lbs of
> spinach. It is also the reason the leaves are removed from rhubarb before
> you buy it. Poisonous, yes but not cumulative. The body can deal with it in
> small doses. Ferric oxalate is sort of an iron spinach mixture. Potassium
> oxalate is a similar compound. Oxlates kill by creating calcium oxalate, an
> insoluble white compound, which clogs up the kidneys. The body produces an
> EDTA like chelate compound to dissolve the calcium oxalate. Calcium is the
> first cousin of iron, and things that dissolve calcium also dissolve iron.
> This is why EDTA makes a great bathroom cleaner, getting rid of all those
> white calcium stains off your pretty chrome. Potassium dumped into the
> stream would kill fish in the immediate vicinity but as it became diluted,
> it would probably not be detectable from naturally occuring amounts. I
> wouldn't be afraid to eat the fish, by the way.
>
> The other developers are salts made from the weak organic acids. Citric:
> oranges, malic: apples, tartaric: grapes, wine, Acetic: vinegar, lactic:
> milk. Most of the weak orgainc acid salts make reasonable good developers
> for pt/pd. Their salts are commonly found in nature. The old time folks
> dismissed the citrates as being too expensive. I saw a price in a 1890
> catalog for citric acid at $12.00 a lb. That was a weeks wages for my great
> grandfather. It was presumable made from orgainc fruit sources. Today the
> soft drink industry keeps the price low. It's made synthetically from
> sawdust today. So much for 7Up!
>
> Sorry about killing all the fish.
>
>
>
>
>
Yes, a sane voice in the wilderness. The oxalates are the things to
worry about here, being the only compound accepted as poisonous. But how
poisonous? My Merck Index lists the LD50 in dogs (don't know why dogs,
curious thought) for oxalic acid as 1 gram per kilogram of body weight.
So if a buch of dogs weighing 50 lbs. ate 20 something grams of oxalic
acid, half of them would die from it.
Be careful, but be sensible.
John
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