① The experiment of "Verifying Archimedes Principle" aims to study the relationship between the buoyancy of an object immersed in a liquid and the gravity of the liquid it displaces;

② According to the weighing method, the buoyancy of an object is equal to the gravity when the object sinks into the water minus the indicated value of the spring dynamometer, that is, f float = f1-F2;

(3) According to ρ=mV and G=mg, the expression of gravity exerted by boiling water on the metal block is g row =m row g=ρ water v row g=ρ water (v2-v1) g;

Therefore, the buoyancy is compared with the gravity g = ρ water (V2-V 1)g exerted by metal block drainage;

④ In addition to verifying that Archimedes' principle is applicable to the case that the sinking object is completely immersed in liquid and partially immersed in liquid, it is also applicable to the case that the object floats on the liquid surface.

So the answer is: displaced liquid; f 1-F2； ρ solution (v2-v1) g; Floating on the surface of liquid.