QWhat happens when a liquid turns into a solid? Can I use it?
When a liquid reaches the temperature of its melting point, it can become a solid. Here are some examples.
[Acetic acid]
The melting point of acetic acid is 16.6 °C. If the room temperature is below 16.6 °C acetic acid becomes solid. However, it is possible that it stays liquid if the storage condition is for example about 10 °C. The reason therefore is the supercooling phenomenon. Acetic acid has a much lower solidification point than melting point. It is hardly solidified when kept still, but it becomes easier to solidify when affected by shocks or by adding different substances. So it is possible that the product was liquid in the storage room due to the supercooling phenomenon but freezed by the shock of placing it on the desk it the laboratory.
[Formalin]
If a white deposit is in the bottle it is not solidified but polymerized and it became paraformaldehyde. The deposit can be liquefied by warming.