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12AX7
Post Harlot
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'Tis; but only the first run got pictures.
Going straight to dichromate is pretty neat, the melt is thermochromic and looks something like blood lava, cooling to orange-red as it freezes. I
suppose it's about as healthy as that sounds, too.
Tim
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blogfast25
International Hazard
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@Antiswat:
Colour is a poor guide when it comes to chemical powders. How we perceive it depends on granulometry, purity, lighting and other factors. Ferric oxide
ranges from ochre to almost black! Individuals also perceive colour slightly differently. Young people's vision often stretches a bit deeper into NIR
than older people's.
No references to PbCr2O7 can be found by chem powerhouses like Merck, Sigma etc etc. One source mentions a complicated route to it and describes the
product as red crystals. See http://chromium.atomistry.com/lead_dichromate.html . Assuming it really does exist then it would hydrolyse to PbCrO4 immediately on
contact with water, as per what was explained above.
Considering that "he doesn't always really give many fucks about the titles he smacks on the bags he sells with chemicals", ergo on balance I
think your product is lead chromate, not lead dichromate. Only elemental analysis for Cr can give the ultimate answer of course.
@12AX7: so you've kept the best to yourself! 
[Edited on 4-8-2013 by blogfast25]
[Edited on 4-8-2013 by blogfast25]
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Fantasma4500
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hmh hmh..
i must draw pictures now! 
http://people.bu.edu/straub/courses/demomaster/images/bloodp...
i can read PbCr2 clearly, then assuming that the rest would be O7, as in PbCr2O7, this has the EXACT same colour as my product does
this however is stated to be PbCrO4
http://upload.wikimedia.org/wikipedia/commons/thumb/8/84/C.I...
http://upload.wikimedia.org/wikipedia/commons/thumb/d/da/Lea...
http://en.wikipedia.org/wiki/Lead(II)_chromate
colours sometimes amaze me, i downright collect colourful liquids in bottles and store them away from UV to pull out sometimes and amaze myself of
what i have seen through time of chemical colours (:
something that really blew my mind was something as simple as copper citrate being deep blue solution, i had it in a yellow plastic container, and
this turned it visually DEEP GREEN!
when i poured out the copper citrate solution with crystals to boil to a solid i did get confused for a minute
i would like to test it, but im just so not glad about handling Cr2O7 in such fine powders, and especially when its lead dichromate..
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blogfast25
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Photo 2 and 3 are clearly, at least going by colour, PbCrO4 ('Chrome Yellow')
Photo 1 is a darker product but that and a half legible label really doesn't constitute evidence of anything at all. It could be PbCr2O7 but
I wouldn't bank on it... Only analysis can be the arbiter here.
What could be worth trying is to take a bit of the top material and suspend it in a bit of water. Then add some alkali to it: it should turn yellow,
according to the principle explained higher up.
[Edited on 29-8-2013 by blogfast25]
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Natures Natrium
Hazard to Others
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I've been messing around with oxides of chromium. I used the high temp NaOH/NaNO3 method of oxidation. The reaction was done about 6 months ago, but
just recently worked up, so I am largely working from memory.
Source of chromium was chromium dioxide obtained as chromium green for pottery purposes. Source of NaOH and NaNO3 was Drano Professional Strength
Crystals, as recommended by a member (I believe it was plante).
A cast iron pot for lead smelting was used. Propane fueled bunsen burner was used as the heat source.
The melt itself was actually quite fascinating to watch. Slowly churning bright green and very hot caustic mud is the easiest description.
Occasionally it would form a crust on top that had to be broken (easily) with an iron file; the file was also used as a stir stick at intervals. I
would have left the crusts to contain the oxygen, but as the melt frothed under the crust it would create a foam that lifted the crust up to the edge
of the pot (and over a bit, in one instance). Whenever the churning slowed down, more of the Drano was added, and the oxygen evolution would pick up
again. This was continued for several hours.
A couple of interesting points:
1. The aluminum turnings contained in the Drano mixture sat at the bottom, and largely went through the entire process unreacted. That is some
passivization, I would have thought that molten hydroxides would have annihilated the aluminum, given the effect of aqueous solutions of hydroxides on
the metal.
2. Just adding more nitrate instead of the Drano mixture also would have been better, but the only nitrate I have available is potassium nitrate, and
the only hydroxide is the sodium salt. This makes the Drano mixture convenient.
3. Towards the end, the melt was even more interesting to watch. As the mud churned, occasionally it would briefly bring to the surface nearly
perfectly translucent crystals of bright yellow sodium chromate, sometimes half a centimeter long. I would imagine that someone with deft hands, iron
tweezers, and a lot of patience could obtain very pure chromate salts this way.
4. I had originally intended to produce the sodium and potassium versions of both chromate and dichromate. However, in the interest of time and ease
of crystallization, I decided to go with only sodium chromate and potassium dichromate.
5. At all times, gloves and eye protection. Fume hood was on.
Now on to a question: What do you guys use to clean up and reduce excess higher oxides of chromium? What is the industry standard?
I have been using lemon juice with vitamin C tabs dissolved in it. It appears to do a good job of reducing the chromium compounds, but I'm aware that
color is not exactly the best indicator of a compounds oxidation state. Thoughts?
The orange mud is the potassium dichromate. It was recrystallized twice from water, but is still very wet. May hang a 'teabag' of dessicant inside
the vial. Yellow is crude sodium chromate, and represents about 1/3 of the chromate recovered from this reaction. The green is more chromium dioxide
than I will probably ever have a use for.
\"The man who does not read good books has no advantage over the man who cannot read them.\" - Mark Twain (1835-1910)
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