Forensics C

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Re: Forensics C

Postby pikachu4919 » February 23rd, 2017, 12:12 pm

I'm having trouble with two things.

First is solubility- sometimes I mess up and I get a soluble powder like calcium nitrate to appear as if it couldn't dissolve, at least at first. Is there a good way to ensure I got consistent results while dissolving powders quickly (since time is so important in this event)? Should I stir or no?

The other problem is that at least when I look at hairs under a microscope I can never see the shape of the hair, just a black strip, which makes them all look the same. Am I just using low quality microscopes? Should I try changing the height of the slide? Or am I just bad at seeing?
Okay, for hairs are you allowed a microscope at the competitions?

At MIT, we had to identify by feel, touch, and taste if you yolo-ed---no microscopes were provided.
Solubility - yeah, sometimes it can be hard to tell. But I'd say if normally soluble powders are appearing like they don't dissolve, it might be because you put too much powder and not enough solvent. For example, with water, for a certain volume of it, there's a threshold on how much powder it can dissolve (and this "threshold" amount also varies from powder to powder, based on Ksp), and any more beyond that threshold will cause a solution to be saturated, in which no additional solute will dissolve. So in other words, you may have saturated your solution.

Hairs:
To answer AllenWang314's question - yes, you can use a microscope for hairs. That's pretty much the only tool you have to confirm the identity of hairs, actually. I can also tell you that taste won't tell you anything about the hairs.

To answer Karp's, idk tbh since I don't know what your microscopes may look like. If you see a thin black strip, you might not be using a high-enough power lens. When I used to do it, I think I always used whatever the highest power lens was. This is especially since hairs are usually so small, you probably won't be able to see much with the low power lens. So in your terms, the height of the slide to some extent, also depending on which lens setting you're on. Even then, it might be hard to see and at that point I might rely on touch.
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Re: Forensics C

Postby 19sawickin » February 24th, 2017, 7:03 am

Is there any good site that can provide practice for ID-ing things like matching fingerprints or identifying certain hairs and fibers microscopically? For fingerprints I'm looking for sites that assist in the identification of distorted fingerprints where you really have to rely on the minutiae to match it which is what most tests have. Also, for hairs I've noticed that for some of the invitationals that I've been to, proctors without any knowledge of the event (I don't really blame them because they don't know any better) take pictures from the internet of microscopic hairs and are misinformed about which animal it actually comes from. Are there any credible sites that I can go to practice ID-ing hairs or fibers?? Thanks

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Re: Forensics C

Postby pikachu4919 » February 24th, 2017, 7:38 am

Is there any good site that can provide practice for ID-ing things like matching fingerprints or identifying certain hairs and fibers microscopically? For fingerprints I'm looking for sites that assist in the identification of distorted fingerprints where you really have to rely on the minutiae to match it which is what most tests have. Also, for hairs I've noticed that for some of the invitationals that I've been to, proctors without any knowledge of the event (I don't really blame them because they don't know any better) take pictures from the internet of microscopic hairs and are misinformed about which animal it actually comes from. Are there any credible sites that I can go to practice ID-ing hairs or fibers?? Thanks
Honestly the best way to do fibers/hairs is to practice on the actual real samples themselves, but I understand if that might be a struggle since some can be quite hard to obtain (c'mon, rules... cow and squirrel hair? really?), but if those aren't readily available, the FBI website is a good source for hair images and for fibers....well, I haven't really found a good one yet tbh bc usually I only rely on burn test to save time during competition anyways, but if the proctor isn't getting them right then that can also sort of be on them for not doing their research well enough - like in my experience, if I ever used images, I made sure to check the web pages the pics were coming from to make sure they were correct, but not everyone does that.

For fingerprints, if all you need is minutiae, then it shouldn't be too bad. Several images reliably tell you what each type of minutiae looks like, and then it's a matter of just looking at fingerprints and being able to recognize those shapes. And then in the real exam time, you look at different sets of fingerprints, compare them to the "crime scene" one, and look for exact matches of certain shapes on the prints.

[I hope that wasn't confusing...I'm kinda tired bc I had to get up for my 7:30 a.m. chemistry lab...]
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Re: Forensics C

Postby cece_a » February 26th, 2017, 11:55 am

Ah, well. Suppose that's better than a single cheat sheet from a couple years ago. Meanwhile, cow and squirrel hair...anyone got any pictures on that?
I was so confused when I heard they switched those two hairs. I guess not everyone has easy access to cows and squirrels. :lol:
There are pictures on google images. I haven't looked up how hard it is to get them, but I think there's a good chance we won't see them until MIT or nationals.
Ha! That's where you're wrong. Was in the regional competition for my area yesterday, and we indeed had to identify those hairs. But they are relatively easy, squirrel hair is very distinct.

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Re: Forensics C

Postby Magikarpmaster629 » February 26th, 2017, 1:29 pm

I was so confused when I heard they switched those two hairs. I guess not everyone has easy access to cows and squirrels. :lol:
There are pictures on google images. I haven't looked up how hard it is to get them, but I think there's a good chance we won't see them until MIT or nationals.
Ha! That's where you're wrong. Was in the regional competition for my area yesterday, and we indeed had to identify those hairs. But they are relatively easy, squirrel hair is very distinct.
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Re: Forensics C

Postby pikachu4919 » March 7th, 2017, 4:01 pm

There are pictures on google images. I haven't looked up how hard it is to get them, but I think there's a good chance we won't see them until MIT or nationals.
Ha! That's where you're wrong. Was in the regional competition for my area yesterday, and we indeed had to identify those hairs. But they are relatively easy, squirrel hair is very distinct.
Image
Ironically I have a small packet of squirrel hair, I'm just not in any classes that would allow me easy microscope access rn otherwise I would try to get an image :cry: but either way I happened to use real horse hair and real cow hair when I ran this event at Wright State invite and the way I got both of those types was through emailing the right people at the veterinary school on my university campus. The squirrel hair is actually available on amazon, surprisingly. Apparently it can be used for fishing lures.
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Re: Forensics C

Postby daydreamer0023 » March 7th, 2017, 8:01 pm

What is the best way to tell the difference between cow and horse hair? They both have course diameters and if ovoid bodies are present, I know it's cow. But I walked into a competition with photographs of hairs and I was completely confused as to how to distinguish between the two - I could find which ones were squirrel, human and bat just fine. :/ Thanks in advance!
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Re: Forensics C

Postby pikachu4919 » March 7th, 2017, 8:37 pm

What is the best way to tell the difference between cow and horse hair? They both have course diameters and if ovoid bodies are present, I know it's cow. But I walked into a competition with photographs of hairs and I was completely confused as to how to distinguish between the two - I could find which ones were squirrel, human and bat just fine. :/ Thanks in advance!
If you had gotten actual hair, from what I've handled, I'd say in terms of the sense of touch, horse hair is a lot thicker and coarser than cow hair (then again I think I used ear hair for the cow and tail hair for the horse, so that observation would make sense anyways). According to the FBI website's pictures, the ovoid bodies will appear as dark specks in the cortex around the medulla which would definitely be rare in horse hair, and another thing is to look at the medulla since that of horse hair has a mosaic pattern while cattle hair does not.
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Re: Forensics C

Postby AllenWang314 » March 30th, 2017, 12:43 pm

Regarding national tests, what is fluorescence? What area (chromat, fibers, blood, or chem) of the event is it about? And what do we have to know about it, and what are websites that can give enough info?
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Re: Forensics C

Postby pikachu4919 » March 30th, 2017, 2:04 pm

Regarding national tests, what is fluorescence? What area (chromat, fibers, blood, or chem) of the event is it about? And what do we have to know about it, and what are websites that can give enough info?
The fluorescence is part of the TLC (thin layer chromat) you'll be doing on samples of different kinds of paints. iirc you perform the TLC on the paint and see if your sample will glow under different wavelength settings of a blacklight, and that's most of what you do.
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