Forensics C

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Re: Forensics C

Post by computergeek3 » January 30th, 2013, 4:07 pm

sciolyynerdd wrote:Hii,

I don't understand what exactly do we have to learn for seeds and pollet & track and soil? Are we supposed to just match photographs?
I think so...the rules are really ambiguous on that...
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Re: Forensics C

Post by pikachu4919 » January 30th, 2013, 6:07 pm

computergeek3 wrote:
sciolyynerdd wrote:Hii,

I don't understand what exactly do we have to learn for seeds and pollet & track and soil? Are we supposed to just match photographs?
I think so...the rules are really ambiguous on that...
You don't say? ... Well, yeah of course tracks are just matching, so there's really no need for notes on that part. Seeds and pollen ... well ... that's REALLY REALLY rare, so I wouldn't bother, actually.
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Re: Forensics C

Post by XXGeneration » February 5th, 2013, 2:37 pm

So just for clarification, are flame test results required in differentiating PVC and PETE? Likewise are they required for PC/PMMA?

Thanks in advance!

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Re: Forensics C

Post by pikachu4919 » February 5th, 2013, 3:26 pm

@XXGeneration: that is the most likely way to distinguish them, since none of the liquids provided are dense enough to be able to do that. As for PC and PMMA, PC sinks in 25% NaCl while PMMA floats in it.
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Re: Forensics C

Post by AlphaTauri » February 5th, 2013, 6:21 pm

XXGeneration wrote:So just for clarification, are flame test results required in differentiating PVC and PETE? Likewise are they required for PC/PMMA?

Thanks in advance!
Flame tests are prohibited on the plastics (because some of them release toxic fumes when lit on fire) - though the event sups may give you written descriptions of what flame tests would be.

PVC is more opaque than PETE, and it's made of larger prism-like granules as opposed to smaller, more rounded pellets...sadly, their densities are pretty much the same, so the only way you can really distinguish them is by look.

I don't have another way to distinguish PC/PMMA, so I'd go with what pikachu4919 said.
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Re: Forensics C

Post by pikachu4919 » February 5th, 2013, 6:41 pm

AlphaTauri wrote:
XXGeneration wrote:So just for clarification, are flame test results required in differentiating PVC and PETE? Likewise are they required for PC/PMMA?

Thanks in advance!
Flame tests are prohibited on the plastics (because some of them release toxic fumes when lit on fire) - though the event sups may give you written descriptions of what flame tests would be.

PVC is more opaque than PETE, and it's made of larger prism-like granules as opposed to smaller, more rounded pellets...sadly, their densities are pretty much the same, so the only way you can really distinguish them is by look.

I don't have another way to distinguish PC/PMMA, so I'd go with what pikachu4919 said.
They usually provide six density liquids for the plastics and maybe burn test results if it helps with the ID. Although sadly both PVC and PETE can sink in the most dense liquid, which is saturated NaCl. So if burn test results are provided, I'd definitely use those to distinguish.

**NOTE: IF ONE OF THE PLASTICS' FLAME TESTS WAS GREEN, THEN IT IS PVC HANDS-DOWN. NO OTHER TESTS NEEDED.
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Re: Forensics C

Post by allisonc524 » February 7th, 2013, 7:00 pm

Can someone provide a good link for identification of plastics? I can't find anything!
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Re: Forensics C

Post by pikachu4919 » February 7th, 2013, 7:09 pm

allisonc524 wrote:Can someone provide a good link for identification of plastics? I can't find anything!
All you really need to do for the plasics is to search up the most important information such as densities, and use that info (specifically densities!) to create a flowchart that works for you. I actually recently edited the Forensics Wiki so it has more info about plastics. You can take a look at it if you'd like.
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Re: Forensics C

Post by allisonc524 » February 10th, 2013, 5:25 pm

To perform flame tests on the unknown powders, is nichrome wire REQUIRED, or is there an alternative? The only thing I can find is platinum wire, and that's less common than nichrome... Any information you can provide would be greatly appreciated!
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Re: Forensics C

Post by computergeek3 » February 13th, 2013, 10:02 am

allisonc524 wrote:To perform flame tests on the unknown powders, is nichrome wire REQUIRED, or is there an alternative? The only thing I can find is platinum wire, and that's less common than nichrome... Any information you can provide would be greatly appreciated!
nichrome is not required...one of the best methods is to take wooden coffee stirrers and wet them. Dip the wet stirrer in the powder and light it on fire. The water prevents the wood from burning and gives a pretty nice burn.
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