4. THE WATERS UNDER THE EARTH
They consist of liquid hydrofluoric acid (HF). It melts at -83°C and boils at 19.4°C. In it are dissolved varying quantities of metallic and non-metallic fluorides, such as boron trifluoride, sodium fluoride, etc. When the oceans and lakes freeze, they do so from the bottom up, so there is no layer of ice over free liquid.