In order to ensure trouble-free operation of some devices, it became necessary to study the conditions of good wetting of iron-nickel alloy products with mercury. As it is known, mercury wettability of a solid body surface in the absence of friction between the surfaces is a function of the difference of free surface energies at the solid-metal-mercury boundary. Wettability depends on the composition of the solid and liquid phases and the condition of their surfaces. When mercury comes in contact with a clean metal surface, the surface energy of the system decreases because instead of two interfaces there is one. If there is any film on the metal, preventing the contact of mercury with the metal surface, for successful wetting, it is necessary either to eliminate in advance this film, or to create conditions that ensure its rupture at the moment of contact of mercury with the metal surface.