Perhaps it is a large bottle, or one made of stoneware. I once found a small bottle of mercury (mercúrio) which has 13.6 times the density of water. I treasured it for years (as a child) before I discovered how poisonous it was. That bottle was heavy - 250 ml weighs 3.4 Kg. Mercury is also expensive, and when I got rid of it to the school chemistry lab, they were very grateful.