Answer to Question 1
Egg white foams alone, without any additional ingredients, are not very stable, and will revert back to a liquid if not used immediately after they are beaten. Often sugar is used as a foam stabilizer.
Answer to Question 2
Ovalbumin and conalbumin are the largest sources of protein in the albumin that supplies the protein for the foam. Ovomucin plays a major role as a foam stabilizer.