This is a great hands-on lesson in which students will try to identify 10 unknown substances by measuring their densities and comparing their results to a list of known densities. It is designed to be used with a set of cubes manufactured by Sciencefirst.com called the Density Cube Set. There is a student worksheet to record data and make predictions, a very detailed 2 page set of teacher notes, a series of review/closure questions, and an answer key. There is no substitute for actually feeling the density differences between identically sized cubes (2.5 centimeters per side) ranging from copper with a mass of 147 grams on the high end to pine at 7.2 grams on the low end. This lab is appropriate for middle or high school. Students will measure, calculate, predict, and infer. It can be completed easily in two 40 minute class periods.