# Getting rid of copper nitrate before melting cement



## WillGreen (Dec 23, 2012)

Dear All, 



A couple of weeks ago, I posted a rather desperate sounding message about the problems I had with getting silver cement ready for melting. 
As always, I got some really great advice and now I want to tell you what I did. Things are still not simple by any means. 

I decided to refine 60 grams of silver - this is enough to see what I am doing. Someone explained to me to that I need 2.8 ml of nitric acid for every gram of silver, so I calculated the amount of nitric acid and put the silver in the flask. It started to dissolve immediately. Someone else gave me the advice to saturate the nitric acid, so, after everything was dissolved, I continued to add silver to the solution until there was no reaction left. I actually needed a lot of silver to do this - perhaps the figure of 2.8 ml is too high? 

After this, I filtered the solution, just to make sure and then I dropped the silver with copper. When the reaction came to a halt, I fished the copper out of the solution and I started to pour off the copper nitrate / nitric acid (? - unlikely, but I‘m not sure) solution. 

This is where the problems started for me in the past. I ruined several crucibles by melting silver cement which was not ready. 

Someone explained that filtering the silver out of the solution is a better way than washing it, so I did this. After filtering and adding water (I used a 800 ml flask), the liquid still looks blue, so I pour the liquid off, fill the flask with warm water, let the silver sink, pour the liquid off and so forth until I end up with a flask in which the liquid is completely clear and colourless. I poured the liquid off and then I wasn’t sure what to do because, although I understand that filtering is a better way of getting the silver clean than the pouring method, it’s still pretty much the same process - so did I really get rid of all the copper nitrate? I sliced a lemon in two and put the juice of half a lemon in the solution (not more than 200 ml of colourless liquid) and there it went: everything turned dark blue. I do not know which reaction this is - I did not want to add hydrochloric acid to anything because I do not want to make chlorides. I just thought that since lemon juice is weakly acidic it will react with copper nitrate, making it a bit more potent. I do not know. What I do know is that the fact that the solution - after adding and pouring off all the water - is colourless does not guarantee that there is no copper nitrate left. I started, once again, to pour off the blue stuff, adding water until the solution was again colourless and then I put the lemon juice of the second half of the lemon in the solution (there was again some 200 ml of liquid in the flask) - and there it went again, although much less outspoken than the first time, I ended up with a nice blue solution once again - it is not very blue, but, still, it is undeniably blue. Now I am going to pour this liquid off and then I am going to melt the silver because I am tired of it. 

Perhaps this is a good way to get rid of copper nitrate, although no one ever told me to add lemon juice to a solution. Perhaps this is an unnecessary step. If it is unnecessary, what I am still doing wrong? Or is the copper nitrate which is left in the flask after the liquid looks completely colourless not important? I am sorry for sounding so obsessive about this, but I really need to stop ruining crucibles. It’s very important to me that my metal is clean, that it rolls well and so on. 

Thank you for reading. 

Merry Christmas and the best of luck for the New Year to you all, 


Will


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## bigjohn (Dec 23, 2012)

Try rinsing with boiling water. I usually rinse twice with boiling water and I've never had a problem


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## Pantherlikher (Dec 23, 2012)

first....never add anything unless instructed...Lemon juice?..sure a mild acid but does it turn blue when added to something else? donno
Are you "seasoning" the crucible properly?...
Not sure about rinsing properly?,... boil in H2O 2-10 x untill you are sure....
Never guess, be sure you're sure...

BS.
Surity is a sign of insanity... Are you sure you woke up this morning?...


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## nickvc (Dec 24, 2012)

Removed as I accidentally double posted. Doh


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## nickvc (Dec 24, 2012)

Will I'm not sure whether the lemon juice , citric acid, will cause problems as I'm no chemist but it will remove some forms of copper so perhaps that's what's occurring. The ruining of your crucibles is I'm pretty sure due to the acid residues in your silver so after rinsing until no colour shows put your silver in a beaker add water and bring to a boil, if colour shows distill and repeat until its clear of colour, easy enough in small volumes a little harder in big quantities and in truth you will probably never remove all the acid but enough to leave few problems.
Be careful adding any acids or other chemicals to your processes unless your abosolutly sure of the result, I can see no real danger here but why take chances, we're not dealing with harmless chemicals most of the time and it's easy to cause yourself or others severe harm.


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## qst42know (Dec 26, 2012)

Based solely on this article you may be dissolving some silver in your citric acid as well.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2590638/


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## MysticColby (Dec 27, 2012)

yeah, too much nitric. It's closer to 1.5 ml nitric per gram sterling.

with each rinse, did you stir the cemented silver? if you just add water to the top of it, there is still liquid in the cemented silver that isn't getting mixed in.

It's a good idea to filter (and wash) the cemented silver after rinsing. If you're not convinced, try it then transfer the cemented silver back to a flask and see how colorless another rinse is.


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