I bought the Lyle & Louise: The Jagged Edge Glass Fragment Identification Kit a few years ago and never got around to using it, so today we finally used it. The Lyle & Louise forensic science kits all center on one murder mystery and each kit has students process one piece of evidence, in the this case we looked at the index of refraction of glass fragments to see if the broken headlight of a truck matched glass found at the scene of a car accident. Previously, I’ve used the Lyle & Louise Bad Impression Bite Marks Analysis Kit, where students made bite mark impressions of their own teeth and learned what to measure and look for in comparing bite marks. You can see my previous blog post on using the bite mark kit here. These kits are interesting but you can’t solve the crime by just doing one or two of them so you don’t get a very satisfying conclusion at the end of the day. They’re also kind of pricey for a homeschool class, running over $100 each, a few are even over $200. They do have a small class edition now that includes a bunch of the kits but only for 1 to 6 students, if I hadn’t already bought the other kits I probably would have gone for that one. If you have a high school student seriously interested in forensic science it would make a nice lab to go along with a semester long class perhaps.
For the glass fragment identification lab, students had to place a bit of pulverized glass on a microscope slide and then a few drops of liquid and a cover slide. The glass samples come in the kit already pulverindeized and labeled (bottle glass, headlight glass, etc). The kit also comes with three different liquids with different refractive indexes, 1.45, 1.47, 1.49. By looking at the glass fragments in these different liquids you can tell if the index of refraction of the glass is greater than or less than the index of refraction of the liquid. The way you identify if its greater or less than the liquid’s index of refraction is by observing the Becke line – a thin white halo around the glass fragment and how it moves as you change the focus of the microscope. Here’s a video that shows what it looks like.
I actually did all 4 glass fragments in all 3 liquids provided by the kit the day before class and didn’t see much difference in any of the results so I looked up the index of refraction for common household liquids to see if we could do a few more liquids to pin point the index of refraction a bit better. I discovered that a number of essential oils, such as clove, cedarwood and cinnamon all have indices over 1.50 so I asked students to bring in any oils on the list that they might have. This allowed students to find a liquid where the Becke line moved away from the glass and gave them an upper limit on the index of refraction. Because we only had two microscopes for 9 kids, I split the students into 4 groups and gave each group one of the glass samples. They shared their data at the end of class. We never would have finished if every group had to do all four glasses and 3-4 liquids. You will need to have a microscope for this kit, you can read about our microscope here. This kit was pricey but I still have plenty of materials to use it over and over again since its designed for a larger class. Even though we may not have solved the mystery, I think these kits are nice because they show how science is used in the real world in a way we don’t usually think about.