I grind up some Fools Gold that contains tiny quantities of real gold. I wanted to make a copper solution for electroplating using ore I prospected. What I got was something far more interesting. The real gold floats right to the top. Impossible because gold is nineteen times heavier than water. Right? Yes and no. If the gold particles are small enough then the effect of surface chemistry overcomes the density effect. The gold picks up a positive surface charge and gets stuck on top of the surface tension of the water. This effect is used to concentrate most metallic ores mined for the past century.