About 1980, the United States Postal Service detached the two-thirds of greater Oxon Hill that was furthest from Washington, D.C. and re-defined that part as a new postal designation, Fort Washington, MD.
A gallon of paint is heavier than a gallon of water. Mostly anything that mixes a solid into the water will be heavier than water. Most homes have a can of Spackle , which is a common liquid for patching drywall and it is almost twice as heavy as water. Of course,mercury is the heaviest liquid, but isn't common around the house anymore. But if you have a mercury switch for turning on your furnace, then that would be the heaviest common liquid by far. Which, I assume, discounts mercury - oil is lighter than water, so two choices would be sugar water or salt water.
500 grams is .5 kilograms. In the video below you can see what burning 500 grams of thermite looks like. A standard 16.9 fluid ounce bottle of water weighs 17.6 ounces, which is equal to 500 grams. You might also find some cans in your cupboard this size. Another option is to use coins.