# Urea, what is chemical formula



## Anonymous (Feb 10, 2008)

I have found lots or chemicals listed under urea. Witch chemical formula is used in AR to drop out the gold? Oh by the way. when one has the brownish particles of gold can they go directly to melt or does one have to go through the trouble to make them gold looking (cleaning Gold Process)


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## Harold_V (Feb 10, 2008)

blacktoad said:


> I have found lots or chemicals listed under urea. Witch chemical formula is used in AR to drop out the gold? Oh by the way. when one has the brownish particles of gold can they go directly to melt or does one have to go through the trouble to make them gold looking (cleaning Gold Process)



I can't help you with the urea question, but I sure have an opinion on the precipitated gold. 

Do not expect precipitated gold to appear as if it's been melted. Regardless of how clean it may be, it will have a dull appearance, and will range in color anywhere from a very pale light tan/orange color through as dark as blackish brown. Gold that has been precipitated from clean, concentrated solutions, using SO2 as a precipitant, resembles ground cinnamon. Color is an indicator of cleanliness in many cases, but it won't be shiny even under the best of conditions because the surfaces are small and reflect light in all directions. As a result, it isn't shiny. You'll notice that if it's clean enough, all it takes to make some of it shine is to abrade it with almost anything---the abrasion tends to flatten the particles and align them such that they form a uniform surface, which becomes the familiar color of gold, and reflects light in a given direction. 

If your objective is clean gold, only a complete fool would melt the powder without washing. Regardless of how clean the solution from which it came may be, unless it was totally free of contamination, the precipitated gold will contain some of the contamination, from drag down, if from no other means. It becomes perfectly obvious why gold should be washed when you do so. What you remove from the gold will be evident in the HCl and water that is used. If it's not removed, it will report in the melted gold, especially if you melt with soda ash, which will reduce the contaminants to the elemental state, and combine them with the gold. It may appear to be clean because you don't see any signs of oxides, but if it's melted without flux, it will readily oxidize, leaving the gold discolored. 

Unless your objective is to recover gold with no regard to quality, you should not skip the washing process. If your objective is high quality gold, you'll slowly come to realize that you can't achiever your goal by a single chemical refining, even with careful washing procedures. 

One of the best tests for your gold quality is how it melts without flux. High quality gold will do so without forming any oxides on the surface. If, when you melt the powder, it won't agglomerate readily and form a puddle that is shiny, it isn't very clean. 

Fine gold will melt in a dish that is coated with enough borax to lubricate the gold and allow it to flow well. When the gold is fluid, it will be a luminescent green/yellow color, and will remain bright upon solidification. It should also pull a deep pipe in the center, as the last bit solidifies. When you have finished melting gold, the dish should still be clean looking, with a slight purple cast to the flux. If the flux is discolored, green, black, or blue, your gold was dirty. If your gold fails to do any of the above, it isn't very pure. If it has a frosted surface, it isn't pure. 

Harold


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## scrapman1077 (Feb 11, 2008)

urea is used to kill the nitric, not drop the gold


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## Lou (Feb 11, 2008)

I don't want to disagree with you Harold, but I've personally seen gold foil form out of HAuCl4 solutions, most likely photo-decomposed. I posted a picture of a vial that has that occurring. The gold floats up top of the syrup solution. I think it would be possible to get gold flakes as a precipitate through some chemical trick, but I'd have to think long and hard before I'd even make a guess as to how. For our purposes, I don't think it matters worth a darn if it drops out as gold grain or that nice light brown powder.


Lou

PS You can do a lot of cool things with gold, especially when you make nano-size particles of it. Pretty purple solutions


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## lazersteve (Feb 11, 2008)

I've seen thin gold foil form at the interface of aqueous potassium oxalate and pregnant BDG (Dibutyl Carbitol) organic phases in solutions.

Steve


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## Harold_V (Feb 12, 2008)

Lou said:


> I don't want to disagree with you Harold, but I've personally seen gold foil form out of HAuCl4 solutions,


No problem. I had foil form on various occasions as well. It will happen easily if you use dirty vessels, contamination with traces of metals. You can also form the foil by using crystals of copperas (ferrous sulfate) instead of dissolving in water, which I've mentioned when testing solutions for gold content beyond using stannous chloride. 

My point is that gold precipitates as a powder that usually does not resemble shiny gold----a pointer for those that are expecting to see the familiar look of gold when precipitating. Don't toss it if it doesn't shine----it usually doesn't. 

Harold


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## Anonymous (Feb 12, 2008)

I dont really care so much the chemical formula as I do, what to buy. there are all types of things labled Urea. When I look at the formulas they are all different. Are they all the same at the same time. (Urea was the first chemical artificically synthisized) ( thats how much I have read) It is crazy to find the right thing. Is there a brand name, a company or does anything labled Urea work. It is crazy. 
Bruce
Blacktoad


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## macfixer01 (Feb 15, 2008)

blacktoad said:


> I dont really care so much the chemical formula as I do, what to buy. there are all types of things labled Urea. When I look at the formulas they are all different. Are they all the same at the same time. (Urea was the first chemical artificically synthisized) ( thats how much I have read) It is crazy to find the right thing. Is there a brand name, a company or does anything labled Urea work. It is crazy.
> Bruce
> Blacktoad





Urea is a distinct compound (NH2)2CO. Without some examples I don't know what it is you're seeing? Urea can be produced in different physical forms such as crystals, prills, flakes, etc., but all are chemically the same. Different salts of urea exist such as Urea Nitrate or Urea Sulfate, but each of those too would be a distinct compound and not the same as pure Urea. Urea has other names such as Carbamate, but that's just a different name for the same thing. Lastly if you're looking at fertilizer grade Urea some manufacturers might list slightly different percentage numbers than others for the same compound.

macfixer01


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## lazersteve (Feb 15, 2008)

Bruce,

If you are looking for Urea for gold refining, you really don't need to. There are several ways around the 'need' for Urea.


 Gently evaporate off the excess nitric from the gold solution before adding any SMB. This process takes between 2 to 4 evaporation cycles with the addition of HCl between each cycle. The gold solution is never evaporated to dryness, just to a near syrup consistency, then the HCl is added. If no brown fumes are evolved when the HCl is added you are done.

 (My Favorite :wink Use a solvent for your gold that does not introduce nitric acid into the solution. There are many of these including HCl-Cl and HCl-H2O2 

Steve


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