Thaw by salt

Tintin and science
Reception
The magnifying glass and fire
Thaw by salt
The lightning in ball
Tintin on the Moon

Our poor Tintin, after having fallen into water in a desert frozen with the country from the Soviets, is found captive of an enormous ice floe. Snowy, so smart is it, cannot alas make a fire. Fortunately, such Master, such dog: the famous fox terrier inherited the direction of the observation of deferring and it noticed that in winter, the human ones pour salt on the glaze to dissolve it. Let us pass on the fact that it succeeded in finding a salt bag in full desert (and that it can read!) to interest us in science.
The limit ice/liquid water for pure water is at 0°C (32 °F) (it is not a chance, it is what was used to define the degree Celsius). But it is precisely because it is pure. Indeed, the chemist François Marie Raoult (not to be confused with François Marie Arouet, true name of Voltaire) discovered at the end of the XIXème century that in the presence of impurities, for example salt, this passage between two states is done at temperatures much lower. Moreover, the lowering of this temperature is proportional to the quantity of impurities until a certain quantity. For salted water, in fact, the melting point is at -21°C (-5.8 °F).
Thus, if the temperature of the ice floe containing Tintin lies between -21°C and 0°C, pure water will be solid but salted water will be liquid. But, the re-establishment of Tintin seems fast. Indeed, salt modifies the physical state of water but doesn't heat it therefore. Only by stopping the reasoning here, Hergé is thus not credible because even if he is not a any more prisoner of the ice, Tintin remains refrigerated.
A factor still should be added : the ice-salt mixture is cooling. Indeed, the dissolution of salt in water consumes energy (bus at the chemical level, the salt of formula NaCl is transformed into ions Na⁺ and Cl^-, it is thus necessary « to break » molecules, which asks for a certain quantity of energy). However, like the matter, energy is not created and does not disappear, but it changes or is transmitted. Thus, the energy used for the reaction is taken in the environment, in fact on Tintin which will be thus even colder than in the ice floe.
But after all, Hergé often showed us that Tintin is a strong solid !