# silver cementing with copper



## clint s (Aug 25, 2011)

hello all i have a small question ok 

i started with 155 grams of .925 silver dilluted with 150 ml of h2o and 150 ml of 70% nitric after the reaction slowed i added 20 more ml of both nitric and h2o i let it sit over night 
then filtered there was some small bits of silver left in beaker i left them for next batch I added at least 3 times the volume of solution with h20 then put copper pipe in solution it started to cement pretty fast it was a fast reaction i am wondering if it is to hot or is there a way to slow the reaction i do dilute the with what i seem to be a lot of h2o can the copper sit over night? or it seems like it spits cemented silver all over if i dont cover is that normal what is the best way to slow reaction other than adding h20 i have tried lots of h2o it seems like the acid is still hot but i didnt add too much nitric from the start i didnt think any way 

Clint


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## kadriver (Aug 25, 2011)

I cement all the silver I process, and use the cemented silver for anode bars in my silver cell.

I have had this happen to me. The spitting you refer to may be that you have too much nitric acid left in the silver nitrate. The nitric acid reacts with the copper, heats the solution, causes bubbling, and even produces red fumes as it dissolves the copper - these fumes are very harmful to breath.

When I dissolve the 925 silver in dilute nitric, as you have indicated above, I use about the same amount of acid/dh2o that you use.

But - I put the reaction vessel inside a corningware casserole dish and set this on an electric burner - outside & away from people and pets. I then turn the heat up gradually until I get to high heat and actually boil the acid and silver.

I let it boil until then are NO MORE red fumes being produced. This may take an hour of more at high heat. Use a heavy pyrex coffee pot with a lid - the kind you can boil liquids in from the 70's (see photo). I would not recommend using a thin walled coffee pot from a modern coffee maker like Mr Coffee.

In your description, it sounds as if you did not heat the acid and silver. In my experience if you do not heat the acid, then the cold acid will not completely dissolve the silver. This would leave a high concentration of acid in the vessel. Cold nitric acid will dissolve copper very easily. When you put your copper in the silver nitrate, the highly concentrated acid dissolves the copper - if you left it all night it probably completely dissolved the copper until noe was left.

I hope it is helpful to you. As always, I am still new to refining and do not claim to be an expert. This has been my experience. Any critique from the forum would be helful.

kadriver


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## Harold_V (Aug 26, 2011)

kadriver said:


> This has been my experience. Any critique from the forum would be helful.


If readers take nothing else from your comments, the one about heating when dissolving is priceless. You have no idea how right you are!
I am at a loss to understand how anyone can refine without added heat, which leaves one with way too many unanswered questions (and more than enough problems).

Harold


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## peter i (Sep 24, 2011)

Harold_V said:


> If readers take nothing else from your comments, the one about heating when dissolving is priceless. You have no idea how right you are!
> I am at a loss to understand how anyone can refine without added heat,



Indeed!

The kinetic rule of thumb is, that each time the temperature is increased 10 degrees C, the reaction rate is doubled.
Roughly speaking:* Increase the temperature from room temperature to boiling, and you have increased the reaction rate around 250 times!*

This also explains why exothermic reaction sometimes run away: The heat evolved increases the reaction rate, more heat is produced, the rate is increased even more, lots of heat........ and your values start frothing over the table!

When doing small scale reactions, a lot of heat is lost to the surroundings. But when you scale it up, the temperature rise of a couple of degrees in the test tube, suddenly becomes a really interesting factor.
I once saw a fellow student make a 100 times scale-up from a "Microscale Chemistry" synthesis of salen-ligand. The result was a fountain of yellow crystals, and not a square inch of the fume hood was left untouched!
It was very impressive, end he spend the rest of the day cleaning the hood.


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