Why do boiled eggs become hard?

            About three-fourths of a poultry egg is plain water in which the albumin protein and fats are suspended. At room temperature, the protein strands are tightly folded in a complex three-dimensional shape. Because the individual proteins are able to move freely, both the egg-white and the yolk remain liquid. But when the egg is placed in boiling water, the protein strands begin to straighten out. The protein ends, normally protected within the folds, become exposed. When the temperature rises to , the open ends join together in bridge-like bonds forming a giant structure. These new bonds prevent the molecules to move                                                                                              thereby making the egg material solid.