PUBLIC Forums => Public Forums => Firearm Identification => Topic started by: fkonidaris on April 06, 2009, 07:59:24 AM
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Hey everyone! I'm currently working on a project for school and am doing distance determination and GSR analysis. I'm getting ready to do the sodium rhodizonate test (am currently doing the modified griess test). Can anyone tell me exactly or approximately how much sodium rhodizonate in grams to use? According to the procedure I have, it only states a sufficient amount of distilled water with a small amount of sodium rhodizonate. Can someone please expand on this? Thanks!
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About the color of strong tea. This aspect of the sodium rhodizonate test is pretty qualitative, so if you can easily see that the solution is brown, you should be good.
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Thank you Cole! Do you by any chance have an approximation of how much in grams that would be? I'm wondering because I need to order the sodium rhodizonate still and my professor wants to know how much to order. Would 5 g be enough to test 10 samples or would I need to go to the next size up of 25 g?
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5g is plenty to process 10 samples.
Z.
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Hi Friend,
The smaller 5g bottle will be plenty for your purposes. Hopefully your sources have indicated to you that a Sodium Rhodizonate solution isn't viable for more than a day, so you need to mix up a new batch for each day you are going to use it. Typically I start with 50-80ml of distilled water in a small beaker and add a small amount (less volume than the eraser on a pencil) of SoRho. I stir and wait a few moments for the powder to dissolve, and see if there is any dark powder residue in the bottom of the beaker. If not, I add another tiny amount. When there are un-dissolved particles at the bottom of the mixture, it indicates a saturated solution and adding more doesn't nessaraily contribute to better results on your tests. Be sure to do a control test on known lead (such as a scribble with the tip of a lead bullet on filter paper) and you're good to go!
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The first time I made a NaRho soln., I saw it described as "saturated" and took it in the literal chemical sense. I must've spent 15-20 minutes just dumping spatula-fuls of the stuff into the beaker. This is partially because it is so dark and fine that when you are constantly stirring it, it looks like it's dissolving when it really just hasn't settled out yet. It was a waste, but I got good reactions...
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The stuff is expensive and considering the fact that the bottle looks almost empty when you first open it, use it sparingly. Start with just enough water to get the job done. I usually use about 30 ml (2.4321395464e-8 acre foot) of water in a 50 ml (4.0535659106e-8 acre foot)* beaker. I add small amounts until no more will dissolve. Then after letting the solution sit for a while to assure that the solution is fully saturated I will decant off the tea colored solution into a clean beaker, leaving the "mud" behind so that I don't spray the undissolved chemical on my tests or evidence.
As Alison mentioned, don't let the stuff sit overnight as it loses potency. I haven't tried it, but I would avoid using hot water, as doing so might speed up the loss of potency.
* :P
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Thank you everybody for your help and advice!!!
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30 ml (2.4321395464e-8 acre foot) of water in a 50 ml (4.0535659106e-8 acre foot)* beaker.
* :P
http://en.wikipedia.org/wiki/Acre_foot
I about fell out of my chair, cracking up. Bob, you rock. :laugh:
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I don't want our farmer friends to feel slighted.
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Hello, colleagues! May I ask, why don't You use sodium sulphide solution? It's cheeper and, if stored in dark and cold place, keeps active quite long (about month or two). It turns lead residues dark-brown.
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Off the top of my head (without seeing it used) I would say that the dark-brown color reaction color could quite easily be masked by blood/dirt on the clothing. Again this is without ever having tried it.
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I apply it on a photographic paper samples (we call it contactogram), and any dirt from analyzed object (including blood) is simply washed away by a cotton wad. The smell is disgusting, although (H2S is a side product of Na2S and H2O reaction).
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Max,
Do you know if there is any published research on this technique. I have not read about anywhere. Are there any false positives to worry about? How does the sensitivity of this technique compare to NaRho?
Thanks
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I'll answer anbout researches more exactly next week, but we use it in Belarus (and our collegues in Russia, as I know) as official method. Sensitivity is quite enough to reveal lead residues (homogenous and speckle, forgive me my terminology ::)). It's part of our standart procedure to determine, have shots from specific firearm taken place after last cleaning or haven't, to define the origin of a hole , and to determine (approximately, of course) the distance of a shot -- if the hole was caused by bullet. We also make tests to reveal copper (as a component of bullet jacket) and antimony (stibium, as part of prime composition).
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To Mr. Jay Stuart
I haven't found any publication in common scientific literature about use of sodium sulphide for exposure of lead residues in common scientific literature. There are some articles in special editions on forensic methods, wrritten in Russian language, but I haven't originals in my posession, only references in official procedure guide (because that articles were issued long time ago -- 1960s -- 1970s). So, all I can is to give details about chemical reactions taking place. Sorry :(
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Max,
Thanks for looking.