Cooling bath

A cryogen mixtures of substances are referred to, which are used for extracting heat.

The effect of the freezing mixture uses three effects.

• The dissolution process of substance A into substance B can be endothermic.
• The cooling substance undergoes a phase transition, the achievable temperature is then the phase transition temperature.
• By adding an additive, the melting point of a substance can be greatly lowered. The physical causes of this effect are discussed in the article melting point depression.

In contrast to most refrigerants refrigerant mixtures are storable in separate form without pressure vessel. Therefore, freezing mixtures are often then used to be if without refrigeration machine with simple means generates low temperatures and held for a short time (eg in a laboratory).

As a method of mechanical manufacture of refrigeration and refrigerants were unknown, before 1860 so we used freezing mixtures to produce artificially cold.

Freezing mixtures with salts

Freezing mixtures of salts with water or water ice use the endothermic heat effects in solving substances for cooling or lowering the melting point of ice.

The temperature change upon release resulting from the energy needed to dissolve the ion lattice of the salts and the Hydratisierungsenergie which is released upon release. For salts with a larger lattice energy than Hydratisierungsenergie the mixture around withdraws the missing energy, the solution cools.

Freezing mixtures of salts in the water can reach temperatures of up to -16 ° C. Better results are achieved in mixtures with water ice, up to -63 ° C. By mixing with ice, the cooling added by the melting of the ice and the subsequent endothermic dissolving the salt in the melt water.

Freezing mixtures with dry ice

Freezing mixtures with dry ice can reach temperatures of up to -100 ° C. Is used dry ice in ethanol (up to -72 ° C), in acetone ( -86 ° C ) and diethyl ether (up to -100 ° C).

Even lower temperatures can be only with the evaporation of liquefied gases, namely to achieve nitrogen and helium.

Very low temperatures below 1 K may be achieved by cooling helium mixture which is based on quantum effects.