Stannous Test Result, Platinum ???

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Chondrule

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I purchased some vintage electrical components to salvage the platinum parts, I had never done this before so wasn't sure what to expect. Turns out, the parts I expected to be platinum actually were platinum, so no surprise there, but what I didn't expect was that some of the other parts were gold.

The gold parts were tips (electrical contacts) at the ends of brass pins which were about an 1/8" in diameter, so I cut these off as short as possible and dissolved them in straight nitric. So far so good, I was left with 2 grams of gold tips in intact condition, which isn't much, but actually it is when it's considered that this gold was unexpected bonus material.

Just to be clear, these gold tips/contacts were manufactured separately from the brass pins they were attached to, they were manufactured separately and then added onto the brass pins, thus when dissolved in the nitric there was a complete separation of the two. All I'm saying here is that the brass pins were not plated with the gold.

So I dissolved these tips in AR. I like to overdo it with the hydrochloric and under do it with the nitric. The tips weighing in at a mere 2 grams, I used 10ml of hydrochloric and started the reaction with 1ml of nitric. Before long the reaction slowed so an additional 1ml of nitric was added, which again got the red fumes started and I knew that more gold was being attacked.

After the addition of the second dose of nitric, shortly thereafter the red fumes subsided yet I had considerable metal left to be dissolved, only about 1/3 of the metal had gone into solution, which didn't make sense since the 2ml total of nitric should've been sufficient to nearly dissolve all my material. So I added 1/2ml of nitric and got no further reaction, this told me it was time to quit, all the gold that was possibly going to dissolve had done so.

So it became obvious that these tips were plated with a thick layer of gold, the question became what was the core material, I figured it was silver since the AR had no effect on them. I rinsed these cores and then heated them to red hot with a torch. The following image is of a few of these cores as they stand now.

3.JPG

Setting the cores aside and focusing on the AR, knowing that I had overdone it with the nitric, I evaporated till the solution turned into crystals at the bottom of the beaker, then added hydrochloric and repeated this crystallization. After killing the nitric twice, I again added the hydrochloric and a couple drops of sulfuric, then filtered the solution and dropped the gold using SMB. The following image is of the precipitated gold and leftover solution after settling, this solution does have that slight residual coloration to it as shown in the image, not the crystal clear that I normally get when precipitating gold.

4.JPG

Using fresh stannous only a few days old, I checked the solution to be sure that all gold had precipitated, which typically it always is in my case since I always overdo it with the SMB. Sure enough, the stannous test proved negative for gold, but what I didn't expect was the brilliant orange result that I got instead, see the following image.

1.JPG

The brilliant orange was an instantaneous result, after about 10 minutes the color had changed more towards brown, see the following image.

2.JPG

Never having had the pleasure of working with platinum in solution, thus never having seen a stannous test of a platinum bearing solution, I need to ask if this is what I'm looking at? Whatever the stannous test is indicating, it sure seems as if whatever is in solution is strong, the test doesn't look to be saying a mere trace of something is in solution, it seems to be saying there's a lot of it.

Unless you gentlemen suggest otherwise, what I'm thinking of doing next is seeing what will precipitate using ammonium chloride. When dissolving the gold in AR, and having noticed that the reaction had ceased, I did continue with the heat for almost an hour, what I'm getting at here is that if these cores are in fact platinum, possibly enough did get into solution that enough could be precipitated with the ammonium chloride.

Or have another idea, I could hit these cores with straight nitric and see if they dissolve, if so then I'll know they're not platinum and are probably the silver that I initially suspected. If the nitric has no effect, I can then add hydrochloric and return to attacking them with AR, this time however continuing the process for much longer than the hour I had subjected them to before, for platinum should take way longer.

By the way, referring back to the image of the cores on the Q-tip, notice that the few cores shown are stuck together with some sort of a transparent, black tinted, sort of shellac, this was the result of heating them to red hot. These cores are not stuck together because of partial melting, the shellac like substance that accumulated on the surfaces is definitely the culprit. Not sure what this is all about, it's as if something came out of the metal, such as how silicone comes out of bronze bushings that are impregnated with that stuff. For all I know, maybe these cores are palladium and this is how that metal reacts when heated, but just as with platinum, I've not ever messed with palladium either, so I'll wait to here from you guys, hopefully one of you will recognize what's going on here.

Anyway, let me know what you gentlemen think, thanks.

So let me know what you gentlemen think.
 

Chondrule

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Howdy Lou, thanks for the response.

I did as you suggested and added zinc, definitely no blue was produced, neither in the solution or the precipitate. Wish I could show the precipitate but can't figure out a way to image the bottom of the beaker, but whatever it is, it's jet black and very fine grained.

5.JPG

I'm curious, what was it that makes you think molybdenum, was it something in particular such as how the metal sweated when I heated it, or maybe it was a combination of things, either way I'd like to know just for educational purposes, it seems there's something I can learn from you here.
 

Chondrule

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Lino1406 said:
Brilliant orange turned brown? So how do you decide negative for gold?

After having finished the test and taking the images, I was done with the brown Q-tip, I placed it on the filter paper I had used to filter the AR solution, both the Q-tip and the filter paper immediately turned black.
 

Chondrule

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In my haste to post the results of the addition of zinc as Lou suggested, I forgot to redo the stannous test and include that result.

Again the Q-tip immediately turned the orange color, exactly the same as before as seen in the image I originally posted, however this time it remained orange, it didn't gradually turn brown. So I guess whatever it is that the zinc precipitated out, it was the culprit causing the brown result.

By the way, I put one of the cores in straight nitric and there was no reaction.
 

Topher_osAUrus

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Chondrule said:
Lino1406 said:
Brilliant orange turned brown? So how do you decide negative for gold?

After having finished the test and taking the images, I was done with the brown Q-tip, I placed it on the filter paper I had used to filter the AR solution, both the Q-tip and the filter paper immediately turned black.

Sounds like the filter needed to be rinsed out further.
 

Chondrule

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Topher_osAUrus said:
Chondrule said:
Lino1406 said:
Brilliant orange turned brown? So how do you decide negative for gold?

After having finished the test and taking the images, I was done with the brown Q-tip, I placed it on the filter paper I had used to filter the AR solution, both the Q-tip and the filter paper immediately turned black.

Sounds like the filter needed to be rinsed out further.

Yes, you're absolutely right. I rinse them till they're white, yet even then it's not good enough to fool the stannous.
 

Lino1406

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Core - normally under gold there is nickel or copper, in this case nickel. Strange to expect platinum since
why we use gold plating instead of full gold
 

Lou

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Molybdenum sweats when heated, doesn't react vigorously at all in concentrated nitric acid and has an orange stannous result.

I'd say molybdenum in solution with gold contamination.
 

kurtak

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Lou said:
Molybdenum sweats when heated, doesn't react vigorously at all in concentrated nitric acid and has an orange stannous result.

I'd say molybdenum in solution with gold contamination.

Lou has mentioned the fact of molybdenum giving a "false positive" for Pt with a stannous test a number of time now --- this tells me there are members that encounter Mo often enough that an actual test for Mo should be posted

I have never done these test myself but have the info in a book about testing for metals other then PMs (as well as testing for PMs)

in these instructions numbers in brackets are a reference to the making of the "test solution" --- Example - (26) is a reference to making a nitric solution to be used for testing --- so I will post the proper "test" solution preparation after posting the actual instructions

there are two instruction for testing for MO - 1) is for MO --- 2) is for Mo steels (Mo/Fe alloys)

1) React with 1 or 2 drops of 1:1 nitric acid (26)

Remove reaction product (nitric drops) with paper or cloth

React again with 1 drop 20 percent sulfuric acid (48)

Immerse a piece of filter paper saturated with a 10 percent solution of potassium ethyl xanthogenate (33)

Note; - per the underlined - that may sounds a bit confusing - it means to dip (or immerse) the saturated filter paper into the drop of sulfuric

A red color identifies positive for Mo

2) For Mo steels which are difficult to dissolve - react to completion with 3 drops of 1:1 HCl (20)

Neutralize with 1 drop of 20 percent NaOH (41)

Acidify with 1 drop 20 percent sulfuric acid (48)

Then add a few crystals of xanthogenate (51)

A red color identifies positive for Mo

Preparation of testing solutions (&/or test reagents)

(26) using 70 percent nitric - for every 1 ml of nitric - dilute with 1 ml "distilled" water

(48) using 98 percent sulfuric acid - for every 1 ml of sulfuric - dilute with 4 ml of "distilled" water ( ad the acid to the water - do NOT ad the water to the acid)

(20) using normal off the shelf HCl (31.45 percent) for every 1 ml of HCL - dilute with 1 ml "distilled" water

(41) NaOH 20 percent - dissolve 20 gram NaOH in 100 ml "distilled" water

(33) potassium ethyl xanthogenate "solution" - dissolve 10 grams potassium ethyl xanthogenate in 100 ml "distilled" water

(51) potassium ethyl xanthogenate - in sold form - do not dissolve

Now I have to order some potassium ethyl xanthogenate because I have a fair amount of scrap I believe to be Mo - or - Mo/Fe alloy

Dave - this is a sample of what is in the book I am sending you for your project

Kurt
 

Chondrule

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Lino1406 said:
Brilliant orange turned brown? So how do you decide negative for gold?
You were right, you nailed it, the cores were composed of a substantial amount of gold, but instead of explaining here, I'm going to post another reply to everyone.
 

Chondrule

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It turns out that the cores were composed of 3 parts gold to 2 parts silver/molybdenum. The 2 parts silver/molybdenum, was composed of equal amounts of each metal.

This 3:2 ratio is why my original solution of AR ceased working once it got past the gold cladding on the cores, a cladding which by the way turned out to have been 24K. When the AR ceased working once it dissolved the cladding, I put it aside while I struggled with the cores, when I eventually got around to precipitating the gold in this AR, I got exactly the same amount in weight that the cores had lost, thus it was 24K.

The 3:2 ratio explains why neither straight nitric nor AR would hardly work, both would work briefly and then cease, I had a beaker of both going simultaneously which I was switching back and forth between. During all this wasted energy, eventually I was bound to make a mistake, sure enough I did when I grabbed my pipette dedicated solely to hydrochloric and added some of this acid to my nitric beaker. This mistake served to tell me that silver was involved.

Using the salt/lye/sugar method I recovered the silver, using SMB I recovered the gold, then I used zinc as a last resort just to see if anything else would manifest, but nothing did. I still don't know what the missing metal was, so I can only think that it was molybdenum like Lou had been saying.

Next time, if there ever is a next time, I'll know to use the inquartation method from the very start when dealing with these contacts, and make sure to use plenty of silver. This ended up being a real pain in the butt, but I learned a lot, so it was well worth it.

Thanks to all who tried to contribute.
 

Chondrule

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Something I forgot to mention above when I did the above update/conclusion to this project, is that I find it strange that the cores having a composition of 3 parts gold and 2 parts silver/molybdenum, at no time did these cores look to be composed of so much gold.

I would think that no matter what was alloyed with the gold, whether it was silver, molybdenum, palladium, or some other white in color metal, that the resulting alloy would have at least somewhat of a gold appearance, yet these cores never did.

Case in point is the following image which I did while partially through this ordeal with these cores. When I made the mistake of adding the hydrochloric to my nitric solution and produced the silver chloride, what I did was process all my solutions to extract all the gold and silver that I could and this is what I was left with.

6.JPG

The smaller gold button to the far left is what comprised the cladding, the larger one is what I so far had managed to wrench from the cores. The small silver to the far right is what I got from using the salt/lye/sugar method, and the remaining button is everything at this point that still hadn't been digested.

That button of undigested alloy still has a decent amount of gold in it, yet the only indication of this is maybe the luster, certainly not the color. But imagine that the larger gold button was added to the two silver in color buttons, thus recreating the original 3:2 ratio of the alloy, I can't understand why the cores would not have had a gold coloration.

Anyway, what I ended up doing was hammering out that remaining button into a disc about the size of a dime, it was very thin and this enabled me to finish this project. I hope I'm making sense here, trust me this is a little confusing to me and I was the one who witnessed everything first hand.
 

Lou

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If I were up for (scary and possibly disfiguring) fun, I would just get a silver crucible and melt them in nitre/and sodium hydroxide. I've done that one before.

The residue is the gold and silver, the molydenum goes into the melt. Vigorously.
 

Lino1406

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The meeting between metal like Ni or Mo with melted nitre is indeed scary (explosive)
 

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