1, put the solid water bag that has lost its temperature into boiling water, and gradually return to transparent liquid after about ten minutes. So it can be used repeatedly. There is a transparent liquid in the handbag, and the viscosity of the liquid is similar to that of water. The bag has a round metal sheet, which is elastic and can be folded back and forth twice. The liquid in the bag solidifies rapidly and the heating temperature is about 40 degrees. The white opacity of the cured body is a bit like water crystallization, but it is not very hard. It's a little difficult as soon as the heat passes.

3, heating principle: to understand the principle of warm handbags, we must first know what is supersaturated solution. At a certain temperature, the solubility of solute in solvent is constant, for example, the solubility of salt (sodium chloride) in water is 36g/ 100mL water at room temperature. When the concentration in a solution is equal to its solubility, this solution is called a saturated solution; When the solubility of a solution is higher than its solubility, it is called supersaturated solution. The liquid in the warm handbag is a supersaturated solution of sodium acetate (CH3 COONa).

Because the concentration of supersaturated solution is too high, it is unstable. When a metal is twisted, a slight vibration is enough to crystallize the solute and turn it into a relatively stable solid. However, this process is exothermic, so the warm handbag begins to heat up.

One advantage of warm handbags is that they can be recycled. As long as the warm handbag is heated in boiling water for about 10 minutes, the condensed solute will dissolve again; This is because the solubility of solute increases at high temperature. In the process of dissolution, the solute undergoes an endothermic reaction and becomes a supersaturated solution again.