An explanation or explanation of thisSummary of Wikipedia that I couldn’t describe better:
The fluids should be differentiable:
- density of around 1000 kg/m3 (originally the definition of the kilogram), more precisely: 999,975 kg/m3 at 3.98 °C. Density anomaly is the property based on hydrogen bonding that water has the highest density at this temperature and increases continuously in volume when it cools below this temperature and even erratically during freezing, so that ice floats on water.
- For most substances, the density increases with decreasing temperature, even over a change in the state of the aggregate.
A chemical substance shows a density anomalywhen its density decreasesbelow a certain temperature at temperature drop, so the substance expands when cooled.
Density anomalies occur in the chemical elements anmon, bismuth, gallium, germanium,molten lithium, plutonium, silicon and tellur,also found in Alloys such as Woodsche’s metal and compounds such as zirconium tungstate or zinc cyanide.Water is the most important substance in which such an anomalyoccurs: on the one hand, the maximum density of the liquid water is reached above 0 °C, on the other hand, ice has a lower density than liquid water.Also some highly polar liquefied gases show density anomalies, e.g. hydrogen fluoride and ammonia.Even when the tin is converted below 13.2 °C into another modification(A-tin), its density changes, but here irreversible.