Forensics C

DarkZephyr
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Re: Forensics C

Postby DarkZephyr » November 27th, 2016, 11:05 pm

How can you tell the difference between cow and horse hair under a microscope if the cow hair doesn't have ovoid bodies? Thanks!

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pikachu4919
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Re: Forensics C

Postby pikachu4919 » November 28th, 2016, 9:52 am

How can you tell the difference between cow and horse hair under a microscope if the cow hair doesn't have ovoid bodies? Thanks!
According to the FBI archives (https://archives.fbi.gov/archives/about ... arch02.htm), cow hair does have ovoid bodies, but if those aren't necessarily visible under the microscope way I'd probably go by medullary index (fraction of the hair shaft that the medulla occupies), or cuticle scale pattern. Looking at different pictures, it seems that the cow hair medullary index would GENERALLY (not necessarily all the time) be smaller than that of horse hair, and I'd probably rely more on that since it's usually tougher to spot cuticle scale patterns under a standard school light microscope.

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Re: Forensics C

Postby sciduck » November 28th, 2016, 5:13 pm

So a practice test said that the best way to lift a fingerprint from a ransom note is ninhydrin. Can someone explain this to me?

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pikachu4919
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Re: Forensics C

Postby pikachu4919 » November 28th, 2016, 9:26 pm

So a practice test said that the best way to lift a fingerprint from a ransom note is ninhydrin. Can someone explain this to me?
I believe that would be because of the use of the fingerprinting method in accordance to the surface it is on. Ninhydrin is effective at lifting fingerprints from paper because it works on porous surfaces (as opposed to a method like cyanoacrylate fuming which is better for nonporous surfaces), which is what paper is. If you want to know the full chemistry behind it I found this: http://scholarlycommons.law.northwester ... ntext=jclc

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Re: Forensics C

Postby sciduck » November 29th, 2016, 5:24 pm

So a practice test said that the best way to lift a fingerprint from a ransom note is ninhydrin. Can someone explain this to me?
I believe that would be because of the use of the fingerprinting method in accordance to the surface it is on. Ninhydrin is effective at lifting fingerprints from paper because it works on porous surfaces (as opposed to a method like cyanoacrylate fuming which is better for nonporous surfaces), which is what paper is. If you want to know the full chemistry behind it I found this: http://scholarlycommons.law.northwester ... ntext=jclc
Thanks. But why would this be better than iodine fuming?

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Re: Forensics C

Postby Lumitailz » November 29th, 2016, 5:33 pm

Another question :D - What determines whether a salt would dissolve in NaOH? I'll definitely do some lab tests in the future, but I want to know the chemistry behind it. For example, I get that calcium salts would all precipitate due to Ca(OH)2, but I don't understand why NaCl dissolves and Na2CO3 doesn't (unless the chart is messed up again).
Which chart are you using? Anyways, determining solubility is mainly based on understanding of chemical reactions (specifically double replacement/precipitation), ions, and periodic trends (often, using periodic trends is how to predict ion behavior in reactions, especially cations).

So, when you put a salt in a solution, think about the cation and the anion of the salt. In this case, for sodium carbonate, the cation is Na+ and the anion is (CO3)2-. Since Na+ is a highly reactive alkali metal (same with the others in its group), it will dissolve pretty much always dissolve, and NaOH itself is no exception. Then, you would have to look at which ions are present: Na+, OH-, and (CO3)2-. None of those can combine to make a solid, insoluble precipitate, so Na2CO3 really should be able to dissolve in NaOH (check in lab). Usually when I use NaOH to do a precipitate test I dissolve the powder in water first and then add NaOH so you can see it better, plus you can check its solubility in water first (that can tell a lot!).
Thank makes sense, thanks! As for chart, I use the one under Forensics Event Supervisors - http://mypage.iu.edu/~lwoz/socrime/ForQual.htm

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Re: Forensics C

Postby 19sawickin » November 29th, 2016, 5:39 pm

So a practice test said that the best way to lift a fingerprint from a ransom note is ninhydrin. Can someone explain this to me?
I believe that would be because of the use of the fingerprinting method in accordance to the surface it is on. Ninhydrin is effective at lifting fingerprints from paper because it works on porous surfaces (as opposed to a method like cyanoacrylate fuming which is better for nonporous surfaces), which is what paper is. If you want to know the full chemistry behind it I found this: http://scholarlycommons.law.northwester ... ntext=jclc
Thanks. But why would this be better than iodine fuming?
I'm not 100% sure why so someone correct me if I'm wrong, but I believe Ninhydrin is the preferred method of fingerprint development today because it can be sprayed on a porous surface directly from something like an aerosol can. Iodine fuming is a bit outdated and requires a chamber and iodine to be heated up and for the object to be placed into the chamber and is really just a hassle. Additionally, other agents need to be applied to the object, or photos must be taken promptly to keep the prints visible, as prints disappear almost immediately after iodine fuming. Hope this helps1

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Re: Forensics C

Postby pikachu4919 » November 29th, 2016, 7:49 pm

Another question :D - What determines whether a salt would dissolve in NaOH? I'll definitely do some lab tests in the future, but I want to know the chemistry behind it. For example, I get that calcium salts would all precipitate due to Ca(OH)2, but I don't understand why NaCl dissolves and Na2CO3 doesn't (unless the chart is messed up again).
Which chart are you using? Anyways, determining solubility is mainly based on understanding of chemical reactions (specifically double replacement/precipitation), ions, and periodic trends (often, using periodic trends is how to predict ion behavior in reactions, especially cations).

So, when you put a salt in a solution, think about the cation and the anion of the salt. In this case, for sodium carbonate, the cation is Na+ and the anion is (CO3)2-. Since Na+ is a highly reactive alkali metal (same with the others in its group), it will dissolve pretty much always dissolve, and NaOH itself is no exception. Then, you would have to look at which ions are present: Na+, OH-, and (CO3)2-. None of those can combine to make a solid, insoluble precipitate, so Na2CO3 really should be able to dissolve in NaOH (check in lab). Usually when I use NaOH to do a precipitate test I dissolve the powder in water first and then add NaOH so you can see it better, plus you can check its solubility in water first (that can tell a lot!).
Thank makes sense, thanks! As for chart, I use the one under Forensics Event Supervisors - http://mypage.iu.edu/~lwoz/socrime/ForQual.htm
Lol that one! I actually used it but I made a lot of edits to it based on info you need and don't need

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Re: Forensics C

Postby homesciencenerd » November 30th, 2016, 11:03 am

Hi everyone, a quick question about calcium nitrate. Has anyone tried the "prilled" reagent form listed on Amazon, or a fertilizer that one can easily obtain that is
calcium nitrate? Will these forms produce a reliable result? Lab grade is quite hard to obtain it seems, and comes with a high shipping cost, due to being a hazardous material. It also must be shipped to a commercial address, which isn't a problem for most teams, but is hard for a homeschool team! Thanks for any help.

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pikachu4919
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Re: Forensics C

Postby pikachu4919 » November 30th, 2016, 5:58 pm

Hi everyone, a quick question about calcium nitrate. Has anyone tried the "prilled" reagent form listed on Amazon, or a fertilizer that one can easily obtain that is
calcium nitrate? Will these forms produce a reliable result? Lab grade is quite hard to obtain it seems, and comes with a high shipping cost, due to being a hazardous material. It also must be shipped to a commercial address, which isn't a problem for most teams, but is hard for a homeschool team! Thanks for any help.
I wouldn't recommend using fertilizer as practice, or you should be extremely cautious about using it unless you're extremely confident it's 100% calcium nitrate because of the fact it could be mixed with other chemicals to make it into fertilizer which could potentially mess with reagent/flame test results (i.e. any trace of sodium will make a flame yellow instead of the reddish-orange color that calcium nitrate should be). The prilled form...I've used it before, I don't like it as much since the little pellets aren't as easy to pick up with tools for different tests (like I've found it hard to put them on nichrome wires for flame tests and they don't dissolve as nicely when trying to make solution out of them). I mean sometimes we used to use the prilled form and literally my coach tried to use a mortar and pestle to crush the pellets into a powder and that wasn't terribly successful...but I'd say it's probably more usable than fertilizer for the reasons I stated earlier.


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