# Corning Double Boiler for Evaporating to remove Nitric



## kadriver (Feb 14, 2012)

I have started to evaporate my gold solutions to remove excess nitric instead of using urea.

The other day I was evaporating a gold solution and it was nearly complete - the solution was getting real dark.

I went to use the head (Navy term for bathroom) and when I returned instead of steam, there appeared to be smoke coming from the container.

I rushed over and added some hydrochloric acid quickly to rehydrate it.

Some tiny gold fleck where seen floating in the solution.

I should have added a crystal of sodium chlorate to redissolve, but I did not.

I think I got it too hot. I lost a tiny amount of gold in the filter - but saved the filter.

Bottom line is I am considering buying a corningware double boiler - all glass with NO metal - to do the evaporations of my gold solutions.

hear is an example of the item I am going to buy:

http://www.ebay.com/itm/Vintage-3-pc-Corning-Ware-Pyrex-Amber-Visions-1-5L-Double-Boiler-Saucepan-USA-/230745621827?pt=LH_DefaultDomain_0&hash=item35b982c543

Does anyone have any experience using this type of method to evaporate AuCl solutions?

I realize that it will probably take longer with the double boiler, but I don't think I will burn it like I almost did as explained above.

Any input would be appreciated.

Also, I used only 20ml of nitric acid to dissolve 34 grams of gold this last refining - does this sound correct?

I started by adding 100ml hydrochloric acid and heating, then I added nitric with a pipette two or three ml at a time, keeping track of how much nitric went in. It took only 20ml of nitric to dissolve the 34 grams of gold completely.

kadriver


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## ReapHer_6 (Feb 14, 2012)

Wow, what a great post to read. I just did almost the same thing today. My sample was on my hotplate. I was boiling down a sample that was overloaded to say the least with nitric. I put a button of gold in it and it tore into it..I removed the button and threw in a gold ring. Once the ring stopped reacting and the red fumes stopped I turned it off. It was loaded with AuCl and really dark green. I left. I returned and say from across the room that the color was lighter.. I found the sample almost hard... alost crystialized... I could break it up and there was some fluid to it but it was like shredded ice in consistancy. I shook my head (here I go again with ANOTHER completely different reaction than I was used to) and added 100ml of HCL.

Please let me know if you are going to try this. I think it makes sense. It is a jacketed reaction chamber. The water would act as a buffer to the temps allowing more precise control of the reaction temps. Weather it will help or hurt recovery / refining efforts I have no idea.

No matter the outcome I love this line of thinking...

You mentioned you were boiling down to remove the excess nitric. Then you said there was a gold fleck in it. And you mentioned losing some in the filter but you kept the filter. I am lost. Which for the record is not a long bus ride... but if you were boiling down the excess nitric, shouldnt all the Au be in solution before you were trying to remove the excess nitric? Just learning, please go easy on me...


John S.
P.S. now at least us Army guys have proof that you Navy pukes take really LONG poops...
This was ReapHer_6... signing off.


LMAO

J/K


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## Noxx (Feb 14, 2012)

Evaporation will certainly take a lot longer with a condenser setup...

Personally, I wouldn't use a condenser. When I was evaporating solutions, I tried to take larger vessels in order to speed up the evap process.

Better yet, try not to overshoot Nitric and you won't have to evaporate at all.


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## kadriver (Feb 15, 2012)

The solution evaporated down and caused some of the gold metal to appear - how it did this I don't know.

Hoke mentions that sometimes if the evaporation is overdone and forms a crust, then gold bits can appear. She says to add a crystal of sodium chlorate (which will produce chlorine gas) to redissolve the bits of gold that formed.

I did not add any sodium chlorate (even though I have some) to form the chlorine gas to redissolve the bits of gold that formed because the solution started to form a crust - a senior moment I guess.

As a result, the gold bits that were formed from over-evaporation, were still in the solution after I added more hydrochloric acid.

Since all the nitric acid had been depleted (and I used very little in the first place - only 20ml or so to dissolve 34 grams of pure gold), the gold bits did not redissolve and remained in the solution.

I could see the tiny pieces when I filtered the solution - it was not much, but enough to see some loss. They were in the filter with the other solids.

That is why I saved the filter - one day I will recover the tiny bits from the filter paper.

Noxx is right - using just enough nitric to dissolve the gold is the best way to go. Also, adding a pure gold button and then watch for all reaction to stop guarantees that all the nitric will be used up (I just learned this tonight, but I have heard it mentioned before).

If I use as little nitric as possible, and add a pure gold button - after all the gold from the original refining lot is dissolved - the gold button will consume all the nitric. I won't have to evaporate at all!

Of course I must weigh the gold button before adding it to the solutoin, and after I take it out to determine how much was used from the button. Then subtract that amount from the final tally of my original refining lot.

It appears that the use of the double boiler will not be necessary if I limit the use of nitric to just the right amount, and use the pure gold button method to consume any excess nitric.

The forum has just saved me about $40 that I don't have to spend on the double boiler - Thank you!

kadriver


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## Smack (Feb 15, 2012)

Noxx said:


> Evaporation will certainly take a lot longer with a condenser setup...
> 
> Better yet, try not to overshoot Nitric and you won't have to evaporate at all.




Yup, that's been key for me, go easy on the nitric. It does not take much at all in HCL to dissolve gold.


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## butcher (Feb 15, 2012)

The double boiler should act like the steam bath, similar to what C.M. Hoke used or describes in her book to evaporate solutions, the main benefit is your temperature is limited, turning up the heat on the stove would not produce any more heat once water was boiling (in atmospheric pressure).

A disadvantage I see, would be long boiling time, you would run out of water, and need to stop process to refill lower pot.

As long as you paid attention to temperature and reactions condition's I do not see a real great advantage to the double boiler.

You could still evaporate the solution too far using the steam bath, to the point of driving off chlorides and changing the gold salts into elemental gold, (as it sounds like you did here)

In Hoke’s, she also suggested a couple of drops of H2SO4, just incase you evaporate too far by mistake, so salts would not form, and of course if refining electronic scrap the H2SO4 helps to precipitate lead from solution as lead sulfide.


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## Harold_V (Feb 15, 2012)

ReapHer_6 said:


> You mentioned you were boiling down to remove the excess nitric.


Please read his post again, *and learn from what you read*. Do not make reference to evaporating by discussing boiling. That sends the wrong message, as if you're endorsing the idea of boiling gold chloride. That undoes all the hard work we do here trying to have readers understand that that is not acceptable, as *it results in lost go*ld. 

Harold


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## ReapHer_6 (Feb 15, 2012)

Harold. 
I had to re read your reply a few times for it to sink in. 

Thank you for pointing that out, as that is exactily what I was doing (wrong). I was boiling down. I thought I read I was supposed to get the sol to a slight boil and watch the top of the flask for the color apearing. I remembering reading that building a bed of sand under the flask and lowering the sand as the sol got lower was the correct method.

If I read (or understand) you correctly, I do not want my solution to boil AT ALL, just heat it enough to see the steam on the top form. Kind of like when I am concentrating my 3% Hydrogen Peroxide to the 30%??? I am just heating enough to evap out the water.

Another AH HA moment. Duh... I will turn off my hotplates and wait to make sure I am straight now.

Please advise.

John S.


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## ericrm (Feb 15, 2012)

harold 
why not to boil ,i have read it 50 time to never boil athe gold solution but why? can gold be trap in steam? or does it do something else?


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## ReapHer_6 (Feb 15, 2012)

I will offer up a novice answer based on the tests of my papertowels that I just cleaned the interrior of my fume hood with. Yes. Most of my values can now be found in my hood or on my paper towels. If this were a game show I would answer this question something like

So I will take "what is yes, for $500.00 Harold"??

lol

Ok, you just made me realize what I was thinking. I too read not to boil. But I thought I read somewhere to boil. So to be honest and not worry about looking dumb this is waht I was thinking. 

I thought I read to boil down the pregnant solition. I thoght you were not supposed to boil AFTER the precip phase. In my mind I was thinking for some reason after the gold dropped, you did not want it flying out in the boil. In essence, and now it makes sense, the opposite would have been better (if you were to err like I did)
If the gold is still in solution it would leave the vessel readily in the vapors boiling off. In return It would have been harder for the gold to leave the chamber if it was back in solid form. Either way I am waiting to make sure I am lined back up in my thinking before I continue any heating of my existing solutions. 

I am understanding now that NO boiling EVER.
Except in the washing phase. Am I heading in the right direction?

John S.


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## niteliteone (Feb 15, 2012)

In a boiling liquid each bubble rises to the top of the liquid and explodes. This explosion will throw a small amount of the liquid out of the container with each explosion.
So as each bubble pops your gold in liquid form goes flying everywhere. :shock: 

Hope this helps
Tom C.


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## ericrm (Feb 15, 2012)

i always end up with very week solution ,that take forever to concentrate.
if the flying droplet is the only reason?
why not just put a watch glass and boil it full power??


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## niteliteone (Feb 15, 2012)

As the watchglass stops the droplets from flying out of the beaker it will also stop most of the water vapor and condense it, dripping it back into your beaker.
It will take even longer to evaporate the liquid with a watchglass on the beaker.

The fastest way to evaporate the liquid without loss is to heat the liquid until it just starts to create small bubbles on the bottom. Reduce the heat a little and have a low humidity draft cross over the beaker.

I usually evaporate with the liquid temperature about 160*F, with the beaker top about 12 inches from my fume hood intake vent.

Hope this helps
Tom C.


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## Harold_V (Feb 16, 2012)

niteliteone said:


> As the watchglass stops the droplets from flying out of the beaker it will also stop most of the water vapor and condense it, dripping it back into your beaker.
> It will take even longer to evaporate the liquid with a watchglass on the beaker.
> 
> The fastest way to evaporate the liquid without loss is to heat the liquid until it just starts to create small bubbles on the bottom. Reduce the heat a little and have a low humidity draft cross over the beaker.
> ...


Thanks, Tom. Well said.
Do not boil. Guaranteed, you will lose values, unless you are working in a closed system. That, of course, wouldn't make sense for evaporation. 

Do NOT speak of boiling when discussing evaporation. It's clear that what I keep saying is true. that one person mentions boiling and the whole damned world reads it as being acceptable. It then takes me weeks on end to get them to pay attention that it is NOT.

*Do not boil.*

Harold


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## ReapHer_6 (Feb 16, 2012)

Harold. I apoligize for the incorrect wording. Please don't vote me off the island just yet...It was a novice mistake. I know that it is a pain to deal with but after all that is why we are all here... to learn from you guys. I think letting down someone you respect is the ultimate way to get something commited to memory. At least it is for me. 

I think one thing that shows time and time again here in this realm is just how important a word, and even more so, a letter changes things. 
Boiling / evaporating.... metabisulphite / metabisulphate... (they might be spelled wrong.)

So I hope no novice sees my writings and then thinks its part of the process.. That would be the opposite of what I am trying to do here. 

Ok, I am going to treat the kids today and take each one of them to school for some one on one time..then I am getting another cup of coffee and watchout!!!

lol

John S.


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## Palladium (Feb 16, 2012)

ReapHer_6 said:


> I am understanding now that NO boiling EVER.
> *Except in the washing phase*. Am I heading in the right direction?
> 
> John S.



You can boil when you are digesting the material to just use a watch glass.


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## jimdoc (Feb 16, 2012)

ReapHer_6 said:


> So I hope no novice sees my writings and then thinks its part of the process.. That would be the opposite of what I am trying to do here.
> John S.



You can always go back and edit a post when it has errors in it. Just mark it as to why it was edited, so the rest of the thread will still make sense. Or maybe ad in red letters at the bottom that the post contains errors, and to read further to see what is corrected.

Jim


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## publius (Feb 16, 2012)

If you are going to use that double boiler unit I would suggest that you place dry sand in a pan on your hot plate, place the first pan onto the sand and add enough Paraffin oil (mineral or baby oil) into the first pot to come up to just past the bottom of your second pot. Leave the top off. The oil bath will keep excessive moisture out of the equation. It will allow for a temperature higher than 100 C or 212 F and the oil will not bubble as long as you keep the temperature low enough. Even and slow heating this way.


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## Harold_V (Feb 17, 2012)

publius said:


> If you are going to use that double boiler unit I would suggest that you place dry sand in a pan on your hot plate, place the first pan onto the sand and add enough Paraffin oil (mineral or baby oil) into the first pot to come up to just past the bottom of your second pot.


I dunno! 
When I started refining, one of the first items I purchased was a water bath. If memory serves, I still have it, somewhere in storage, likely in perfect condition. 

My opinion?

Totally useless. You can't provide enough heat to facilitate respectable evaporation. Believe me, I tried. 

Adding oil, then heating? You might avoid water condensate, but the oily fumes are a fire hazard, and aren't exactly my idea of something desirable on my glassware. I'm not sure I'd endorse that idea, although I confess, I never gave it a go. Please correct me if I'm wrong. 

A perfectly acceptable evaporation process can be accomplished with a gas fired hotplate, or most likely, even an electric hot plate. Don't know about the electric one---I never tried. I knew from the outset that I needed a gas flame, so that was my choice. It can come from natural gas, or propane, and small hotplates are not expensive.

My advice to you folks is to not complicate things. KISS

Harold


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## publius (Feb 17, 2012)

Oil baths are common when heating reactants below 350 degrees F but above the boiling point of water. Slow and even heating is the purpose. See:
http://msds.farnam.com/m000712.htm 
The flash point of mineral oil is about 400 degrees F. I would use electric heating and as I described above.


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## Harold_V (Feb 18, 2012)

A good day for me, as I learned something new. Thanks, publius.

Harold


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## publius (Feb 20, 2012)

Harold,
I am humbled by your praise.
Robert


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