the factors??

Wikipedia is your friend:

http://en.wikipedia.org/wiki/Specific_gravity

Specific Gravity = (Density of substance) / (Density of H2O)

http://en.wikipedia.org/wiki/Density

Density = Mass / Volume

Density and specific gravity are material properties. Water is denser than gasoline. Stone is denser than water. Iron is denser than stone. Lead is denser than iron. Gold is denser than lead.

Factors which influence density and specific gravity are the atomic weight of the material, the way the protons, neutrons and electrons are all packed together. You can find the atomic weight of each element in the periodic table of the elements.