2. Control the temperature of the liquid with the thermocouple.
3. Dip samples of threads into the cooling water, by step of 5°C; observe the “melting” and measure the
rate of “melting” (in the ranges of temperature where a change of behaviour occurs, we make the
measure all the 2.5°C).
Figure 7 : experiment
Figure 5 : « cheveux d’ange. » Figure 6: tools
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III.2.2.2. Measure of the melting point of «cheveux d’ange»:
Control the melting point by means of the kofler hot bench.
III.2.3.1. Measure of the speed of dissolution at different temperatures:
Cf. annexe 3.
Temps de dissolution des cheveux d'ange en fonction de la
temperature du milieu
Temperature du milieu en °C
Serie2 4 4 4 4 2 2 1 1 1 1 1 0 0 0
40 42.5 45 47.5 50 52.5 55 60 65 70 75 80 90 93
We observe that the dissolution of «cheveux d’ange» plunged into water is never immediate;
however, stirring the solution helps this dissolution.
The graph shows that the water temperature has an influence on the dissolution: the higher is the
temperature, the quicker is the dissolution.
III.2.3.2. Measure of the melting point of «cheveux d’ange»:
The melting of « cheveux d’ange » begins at 100°C and is complete at 120°C.
III.2.4. Discussion/ Interpretation:
The melting of «cheveux d’ange» occurs between 100°C and 120°C. Indeed, the cheveux d’ange
material is not pure. However, it is not the fusion which takes place in this phenomenon but a dissolution
of the toffy in solution, because the melting point is superior to the temperatures we used.
The size of the “cheveux d’ange” (their diameter) and the temperature of the solution influence
the dissolution kinetics. Also, because the disappearance in solution of «cheveux d’ange» was realized
with some tap water, it is probably important to take into account the solution concentration to be able to
estimate the speed of dissolution and the efficiency of the solvent at a given temperature. However, a
mechanical agitation can largely facilitate the dissolution.
To improve the dissolution, we can increase the time of contact between the solution and the