Why should ether be evaporated in a water bath instead of directly on a hot plate?

Ether is a higly volatile and flammable substance. It should not be heated directly on the hot plate because combustion may occur. Usually, direct heat is not applied when heating with ether. The presence of water bath allows gradual increase in temperature and prevents direct contact to heat. When evaporating ether, precautions must be done. Appropriate temperature must be applied to prevent combustion. Aside from volatility and being flammable, ether can be good solvents, anesthetics and usually tasteless.

Ether fumes can combust if heated directly. On the other hand, heating in a water bath causes a slower and more controlled rise of temperature, since one would have to heat the entire volume of water as well as the ether itself. This means that the ether can be vaporized without causing a rapid rise in temperature and causing it to burn.