A gallon of milk seems to weigh more than the fluffy pillow you sleep on. You probably wouldn't confuse these two materials nor have trouble thinking about their density. But how about steel versus iron? Aluminum versus tin? Density is a very measurable property even for solids that have a similar appearance. In this unique kit, students determine the density of an unknown metal slab and compare it to previously measured metal cubes. Very clever and very involving for students. Classroom set includes 15 sets of materials, enough for 30 students working in pairs.