Why water boils, and the milk runs away?
You can stand for a long time at the slab and wait for the milk to "rise", but it is worth a minute, as it will surely run away. Although the water left on the included plate threatens only throw out, and it is not immediately.
Of course, it’s not about the law of meanness, but in physics. During the boiling of liquid throughout its volume, vapor bubbles are formed. Liquid molecules inside them evaporate, thereby grow bubbles. Under the action of the pushing force, they rise up, reach the surface, after which the pairs of them go out.
When water boils, no barriers. With milk, the situation is different. In the process of its boiling on the surface, a dense film appears, which does not allow pairs formed when boiling, go out. Thus, they displace the milk from the pan and it runs away. And pretty fast.
To avoid milk rivers on the stove, there are two ways. The first is constant stirring, during which the dairy film collapses and couples freely leaves liquid. True, in this case you are sentenced to stand at the slab. If you use an aluminum saucepan, it is possible to stir milk just less often, since the edges of the film sticks worse.
The second way is more complicated, but reliable – water sauna. Water poured into a large saucepan and the container with milk falls into it. The fact that the boiling process requires continuous summing of heat, which is transmitted only in the presence of a temperature difference. In the case of the water bath when the water in a large pan boiling, its temperature is 100 ° C. But the same temperature will be installed in a saucepan with milk! Since the temperature in the saucepan will be the same, the milk will not get the heat desired to boil. It will be possible to quietly go to their affairs and not be afraid that the milk "will run away". The disadvantages of this method only two. First, it is necessary to use two pots instead of one. Secondly, it takes more time.