# Stannous Chloride Testing Solution



## NobleMetalsRecovery (Jun 30, 2007)

Does anyone know? Is there a FALSE POSTIVE for stannous chloride? In other words, can stannous chloride raact with anything besides gold chloride to form a purple or black stain on filter paper.

If I put a drop of the solution in question on filter paper, and then put a drop of KNOWN good gold testing soltion, if the blot turns black, am I certain that it's gold?


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## NobleMetalsRecovery (Jun 30, 2007)

spelling error: is should be "react"


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## NobleMetalsRecovery (Jun 30, 2007)

I quess it's just to late at nite for me to be posting.


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## Harold_V (Jun 30, 2007)

Palladium will often yield a reaction that can be confused with gold, although they are not the same and can be discerned from one another. If you use a spot plate, when you rinse the test from the cavity, if you have gold, look for the characteristic purple stain on the dish that doesn't rinse off. Palladium never yields the purple color. Palladium tends to have some green or brown overtones in the reaction that are lacking in the gold test. 

One thing is certain. If you prepare your stannous chloride and dispense from a dropping bottle-----you should test it against a standard solution regularly so you can tell when it ceases to function properly. I noticed that as it changed color and became more opaque, it also lost it's efficiency, and finally quit working completely. As it declines, it gets more and more difficult to determine the reactions. 

It's a good idea to have a standard DMG (dimethylglyoxime) testing solution on hand to test for palladium when you're in doubt. The tiniest amount of palladium yields a canary yellow precipitate. It is also useful for determining the presence of nickel----a drop of solution in a cavity of a spot plate, followed by a drop of ammonium hydroxide, then a drop of DMG will turn a beautiful pink (from dark blue) if nickel is present. 

Read Hoke's book on testing these elements, and follow the instructions provided. It worked for me. 

Harold


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## lazersteve (Jun 30, 2007)

Noble Metals said:


> Does anyone know? Is there a FALSE POSTIVE for stannous chloride? In other words, can stannous chloride raact with anything besides gold chloride to form a purple or black stain on filter paper.
> 
> If I put a drop of the solution in question on filter paper, and then put a drop of KNOWN good gold testing soltion, if the blot turns black, am I certain that it's gold?



Steve,

If iodine is present in the unknown solution you are testing, you will get a very dark black/purple spot with Stannous Chloride.

Steve


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## AuMINIMayhem (Jun 30, 2007)

when using stannous after dropping out the gold with SMB, I put a drop of the testing solution on a folded up coffee filter with a drop of the solution "post-precipitation" to test for any leftover gold.. the spot did* not *turn purple anymore but instead turned brown.. in fact it looked exactly the same shade as if I had scorched the paper with a torch.. What does that indicate? I'm assuming it just indicated too much SMB and/or Urea, because I did go a bit overboard with it  (this was my first "successful" attempt with AR). Would I be correct?

Thanks,
Derek


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## Harold_V (Jun 30, 2007)

In my opinion, you should now test with DMG. The reaction you witness could be platinum or palladium----but may not be. If there is palladium in solution, you'll know beyond a shadow of doubt. 

Platinum, in a given level of concentration, will often have a reaction that resembles the color of coffee, but if your source of materials excludes the chance you'd find platinum, the color you see is likely unrelated. Be on guard if you're processing any dental scrap. 

Harold


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## PhillipJ (Jun 30, 2007)

Ok now. So if a guy has gold in AR solution, and suspects platinum, the spot plate will always show gold. Right? 

Aside from dropping either the gold or platinum one wouldn't know for sure if there was platinum?

Also. Can any platinum be dropped after the gold has settled out?


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## NobleMetalsRecovery (Jul 1, 2007)

Thanks to all who replied to my inquiry.

Excellent info. Very helpful.

I have a situation where the AR solution does NOT test positive for gold, but the leftover sediment (greenish/yellow) turns black when tested with the gold testing solution.


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## Harold_V (Jul 1, 2007)

PhillipJ said:


> Ok now. So if a guy has gold in AR solution, and suspects platinum, the spot plate will always show gold. Right?


 
Yes. But it's important that your stannous chloride solution be fresh. It loses it's ability as it oxidizes. Even with a heavy concentration of platinum, you will still get a purple stain, even if the gold content is low. In that case, it may be masked to some degree and you might not see the reaction in the spot, but the stain will remain when you rinse the spot plate. Platinum, in concentration, yields a reaction that looks much like dark coffee. 

Just having palladium and gold together can be confusing. Adding platinum makes it somewhat worse----but as I said, each of them have a distinctive reaction, so you have to get used to what they look like, especially when they're mixed----and maybe even do further testing (using DMG, for example) to help sort what you're seeing. I don't recall ever having gold present and not being able to identify it, although if you had your solution down to just a few parts per million, that might be a case where you could overlook traces. Not much to worry about considering the value would border on nothing. The stannous chloride test for gold is VERY sensitive, and will detect amounts that are hardly worth recovering. 



> Aside from dropping either the gold or platinum one wouldn't know for sure if there was platinum?



That's entirely possible when working with a solution that contains a serious amount of gold, but you can do a test with ferrous sulfate to eliminate the gold, then test the solution for values if there's any question about content. Here's what you do: Place a drop of your solution in a spot plate cavity, then apply a crystal of ferrous sulfate. The crystal will precipitate the gold as a very thin sheet, or fine powder, leaving behind any other values. You can then test the cavity with stannous chloride to see if there is any reaction. If you get a purple reaction, you know the gold is not yet all down. If so, start another test, and stir the tiny sample with a glass rod, exposing all of it to the ferrous sulfate. The sample will change color as the gold precipitates. It's a good idea to have a tiny amount of ferrous sulfate left, which will indicate that the gold is all down. When there is no further action or color change, apply a drop of stannous chloride. With the gold gone from the solution, you can now see if there are other values present. 



> Also. Can any platinum be dropped after the gold has settled out?



Absolutely. That's how you effectively separate the two. You won't get a perfect separation when you have them mixed, for the first thing to be precipitated will always drag down a trace of everything that's in solution with it. When you wash what ever comes down first, you'll remove some of the dragged down values, which can be recycled for later recovery. My choice was always to precipitate gold first, but I worked with, primarily, gold solutions. The Pt group metals were often in such low levels of concentration that they could not be recovered without evaporating the solutions to concentrate them. I've mentioned time and again that the Pt group metals do not precipitate from dilute solutions. They don't. Not at all. Armed with this knowledge, and a future plan of processing everything through my reduction furnace, I simply poured all my solutions (that bore traces of values) in my stock pot, where they were precipitated on scrap steel. Residues from the stock pot were then combined with all my other waste materials and furnace reduced to recover the values. You need not do the furnace work, the residues can be chemically processed just as well, so recovering traces of values on scrap steel to concentrate them is not a bad idea. All depends on how badly you want to get your hands on the values. I was willing to wait for years-----and it turned out to be about 20 of them before I recovered mine. It was a wonderful savings plan. Remember-----I've told readers I retired at age 54. Couldn't have done it without refining

Harold

Edit: changed word "than" to "then"


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## Harold_V (Jul 1, 2007)

Noble Metals Recovery said:


> I have a situation where the AR solution does NOT test positive for gold, but the leftover sediment (greenish/yellow) turns black when tested with the gold testing solution.



In the dark corners of my mind, I recall one incident, where I recovered gold from a complex gold ore-----a gold telluride. The test would turn dark gray or black with time--- after the gold was precipitated. No purple stain, however. Do you have any reason to suspect tellurium?

Harold


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## NobleMetalsRecovery (Jul 1, 2007)

No reason to suspect tellurium.

I think I need to review my methods for making the gold testing solution. I have always made it by dissolving some tin in muriatic acid. I now have stannous chloride available, and have been adding a little of that to the testing solution.

I would expect there's a post on the forum for making the gold testing solution?


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## PhillipJ (Jul 1, 2007)

Thanks a bunch Harold. You are a blessing here.

I finally bought a copy of Hoke's book and read the part on testing solutions this morning. But, I don't remember seeing the part about ferrous sulfate. It just said "a trained eye, in time".


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## NobleMetalsRecovery (Jul 1, 2007)

I mixed up some fresh gold testing solution, with stannous chloride. Works great. My old solution was going bad.

I filled a dropper with some gold standard solution so I can keep a check on the gold testing solution to make sure it is still effective.


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## Harold_V (Jul 1, 2007)

Noble Metals Recovery said:


> No reason to suspect tellurium.
> 
> I think I need to review my methods for making the gold testing solution. I have always made it by dissolving some tin in muriatic acid. I now have stannous chloride available, and have been adding a little of that to the testing solution.
> 
> I would expect there's a post on the forum for making the gold testing solution?



I'm very anal about my methods and instructions, and for good reason. They work!

May I suggest to you that you buy a copy of Hoke's book, and follow instructions you find within? 

My attitude about testing is that it's only as reliable as your methods and experience. Hoke will teach you the proper way to do your testing, and what to expect. Instructions for building your own stannous chloride solution is included. The importance of following a regimented system can't be over emphasized-----for the strength of your testing solution(s) will dictate the results of your tests. Making standard solutions is very much a part of learning to interpret the reactions you'll experience. 

Making any standard or test solution from unknown levels of constituents will keep you off balance for a long time, for the results will vary widely and have little meaning in training your eye to know and understand what you're seeing. 

So you'll understand, I'm very sensitive about this matter. I am not an educated person, having completed little more than high school. I have no notion that I'm a chemist, therefore I have always placed myself at the mercy of someone that is, or has far greater knowledge on the subject of refining than I possess (Hoke), and have been rewarded with success beyond my wildest dreams. I recommend you do the same unless you have greater knowledge than that contained in her book. I promise you, if you continue the course, you won't be disappointed, and will receive far greater value than the cost of the book. 

Harold


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## lazersteve (Jul 1, 2007)

Noble Metals said:


> mixed up some fresh gold testing solution, with stannous chloride. Works great. My old solution was going bad



Steve, 

I've had similar problems with stannous chloride made from tin powder and HCl. I've had good luck making my old batch reactive again by adding an additional touch of tin powder and reheating. Ocassionally, I have to add a few mL of HCl as well. My homemade stuff gets unreliable after about a week if kept stoppered. I follow Hokes instructions by testing a known sample of Auric Chloride before I test any unknowns. This way you can be sure your Stannous Chloride is good for the test.

Steve


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## NobleMetalsRecovery (Jul 1, 2007)

I have an extensive collection of books on this subject, about 100 different books. I just checked, I have 2 books by Hoke. "Refining Precious Metal Wastes", printed in 1940 (1st edition).

Also, "Testing Precious Metals", 1946, 3 rd. edition. Looks like it's time to hit the books again.


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## AuMINIMayhem (Jul 1, 2007)

Harold_V said:


> Yes. But it's important that your stannous chloride solution be fresh. It loses it's ability as it oxidizes.



yeah, that's why I make "poor man's stannous" everytime I run a batch and then discard it afterwards. I happen to have a lot of scrap tin laying around (I have to seperate everything before I take it to the recycling center, that's how we have to do our garbage here). I just dissolve a couple snips of clean tin in some HCL and then filter off any sediments.. works like a charm, takes less than 15 minutes to make.


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## AuMINIMayhem (Jul 1, 2007)

Harold_V said:


> but if your source of materials excludes the chance you'd find platinum, the color you see is likely unrelated. Harold



yeah, there is little to no chance there was any Pt in that last batch I did.. I'm wondering if it was just too much SMB or something else.. initially when I was getting the positive purple reaction it was pretty much instant.. after dropping the gold, I tested again the reaction took much longer, on the order of minutes instead of a few seconds and once it was finally done it had the appearance of being "scorched" for lack of a better descriptive term.. I should have taken pictures.. 

actually, that's not such a bad idea.. if anyone is interested, perhaps we could have a section in the gallery threads of photos of different reactions with a description of the reaction, the chemicals used and what the results are showing.. just a thought.. 

Thanks again HV.. 
Derek


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## Anonymous (Nov 7, 2007)

It's easy enuff to make yer own stannous solution. And, if you are going to be working for long periods, or over a couple days, Just drop a piece of tin in it. It'll slowly dissolve over several hrs, extending the life of the solution. Just don't cork the bottle whilst it's dissolving as the gas will pop the cork, or the bottle / test-tube.


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## Palladium (Sep 1, 2011)

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