Nothing really protects the beaker. The beaker is made of glass and glass melts at very high temperatures, so a flame you use in your science class won't change the glass. Although, I have heard from my science teacher that when the bottom of the beaker is heated and cooled repeatedly, as it is in science classes, the glass might shatter after too many times of this.
Displacement is usually the method that is used to measure the volume of an irregularly shaped object. The object is simply submerged in a liquid and the volume of liquid that is displaced is measured. As an example imagine a 100 ml graduated cylinder with 50 ml of water in it (half filled).
Displacement is ordinarily the strategy that's utilized to degree the volume of an irregularly molded question. The protest is essentially submerged in a fluid and the volume of fluid that's displaced is measured. As an case envision a 100 ml graduated barrel with 50 ml of water in it (half filled).