Here is an example of the canisters once they have been modified to float, sink and suspend.
The kids really enjoy this lab, although we kinda took the fun out of it by making it a density unit test! (It is the only test that I could find that required real application.) Along with my awesome colleagues, we set up 28 lab stations (1 per student) as pictured below. If it were not a test, kids certainly could have worked in groups and shared materials, but I'm a big fan of very small groups or individual work on labs when possible.
Note: Students were asked to bring a dish towel to work on, because as the containers are taken in and out of the tub the tables get soaking wet. (The brown paper towels the school provides, just couldn't hack it.)
Off to plan some activities for elements and the periodic table...