 Of the many, many strange things in my office that have either been accumulated by me or found and recovered since moving in, the most useful has been this painted gold brick, which has mostly been used as a counterweight to make a crude but effective overhead visualiser. And I've often wondered, well, what is it actually made of? Well the easiest way to figure this out was with density, which requires weighing and dividing by volume. Volume of course is trivial, as the simple shape removes the need for some kind of fancy water displacement experiment. The brick is 20.3x7.6x3.9 for a total volume of just over 600 cubic centimetres. Knowing that something this heavy would do irreparable damage to some expensive and well-calibrated precision equipment, if this thing went anywhere near our analytical balances, and also disappointed that my preferred description of chose was neither a metric nor SR unit, I had to make do with some less precise bathroom scales transported from home, insert a problematic lockdown weight gain joke here. This showed that the brick weighs about 6.9kg, a very nice, rounded number. To put this weight in perspective, this is equivalent to about 20 of these drinks cans that I have lying around after an event which all passed their use by dates before the pandemic even started. In total these cans occupy over 10 times the volume of the brick. A simple division of this 6.9kg by 600 cubic centimetres yields an answer of 11.47 per cubic centimetre, which is a shade over but well within the error range for pure lead, which has an established density of 11.34g per cubic centimetre. The only other competitor for something with this density would be Thalium, but given that a brick this size would cost over $3,000 and the fact that I am still alive after handling it suggests this is highly unlikely. For comparison, 600 cubic centimetres of water would weigh only 0.6kg, and a quick division by the molar mass of water yields about 33 moles of water, that's about 20 septillion water molecules. By lucky coincidence, that's about the same as the number of atoms that would be in the lead brick. So why is the brick so much heavier? The overwhelming majority of the mass of an atom comes in the atomic nuclear switch by volume is an incredibly small part of the atom. As the mass of each element increases, their size doesn't change by an equivalent amount. I'm going to almost oversimplify here for the sake of time, but the nucleus of an atom increases in size across the periodic table, and the positive charge holding the atom together also increases. This exerts more of an electrostatic force on the electrons, reducing their size going left to right on the periodic table. While going down each group, elements still get larger, it means that the metals found in the bottom right where we can find lead tend to be smaller than we'd expect if it wasn't for the complexities of electronic structure and special relativity. The volume of a lead atom is approximately twice that of aluminium, but that means it packs in almost three times as many of electrons per volume with an atomic nucleus that weighs nearly eight times as much. In fact, going by density, a brick of aluminium this size would contain about twice as many atoms, but contain only half their mass. That means you get a lot of mass for not very much space, and means if you drop a litre of water on your foot, it will likely hurt, but if you drop this on your foot, you might end up in hospital.