The study of the laws that govern the spreading of liquid metals on different types of solid surfaces is one of the most important problems of the physical chemistry of surface phenomena in melts and modern materials science. The rate of spreading and the character of the phase interaction on the contact boundary help determine the physical and strength properties of materials obtained by liquid-phase sintering or impregnation, as well as the service characteristics of goods whose production requires soldering, welding, or similar operations. The spreading of the liquid is generally accompanied by dissolution of the solid in the liquid, interdiffusion of the components, absorption, and chemical reactions leading to the formation of new phases. This accounts for the interest in determining the kinetic laws that govern spreading in metallic systems with different types of interactions among the components. We studied the kinetics of the spreading of copper and tin on iron, cobalt, and nickel. Binary systems of copper with iron, cobalt, and nickel are characterized by complete (copper-nickel) and limited (copper-iron, copper-cobalt) solubility in the solid state. No intermediate phases are formed in these systems, and solubility in both the liquid and the solid states changes within broad ranges [ 1]. The metals of the iron group combine with tin to form intermetallic compounds (stannides) with homogeneous regions of different sizes [ 1] and high negative heats of formation [2-4]. Metals of the iron group and tin also form limited solid solutions. The cobalt-tin and nickel-tin systems are characterized by unlimited mutual solubility of the components in the liquid state. This is a contrast to the iron-tin system, which has a region in which the components are immiscible in the liquid state. In many metallic systems (including the systems we are examining), spreading is completed in hundredths of a second. This makes the phenomenon more difficult to study experimentally. Recording the process requires the use of highspeed photography. Of particular importance is the method used to bring the liquid melt into contact with the surface of the solid. Two methods are known, each of which has certain disadvantages. In one approach, a drop of liquid metal is formed by melting inside a container above the substrate. The drop then falls onto the substrate from a short (5-8 mm) height [5-8]. The drop acquires downward acceleration as it falls, which causes it to vibrate after coming into contact with the substrate and complicates the analysis - particularly during the initial stages. The amplitude of the vibrations and, thus, their distorting effect are greater, the greater the height from which the drop falls and the greater its mass. To minimize the vibrations, during the initial moments after contact (r < 0.01 sec) the solid plate (substrate) is slowly raised toward the drop [9]. The drop comes to rest on a substrate composed of an "inert," poorly wetted material. In this case, the vibrations of the drop begin after the drop separates from the underlying substrate. The shortcomings of this method are the need to choose a suitable material for the "inert" substrate and the fact that during spreading the drop is temporarily positioned between two solid surfaces (the top plate being tested and the "inert" bottom plate). Nevertheless, reliable data can be obtained on the kinetics of spreading during the initial stages (r < 0.01 sec) by using a bottom plate that is raised toward the drop.