Coalescence and fragmentation of equal and unequal liquid-drop pairs are studied using a new experimental technique in which mercury drops collide while sliding on a horizontal glass surface. The limits for coalescence measured as a function of the incident relative velocity and impact parameter are found to be similar to what has been reported for free-moving drops of other liquids, while new correlations are found to occur among the number, size, speed and angular distribution of fragmentation residues. The predictions of various models, including a dynamic theory originally developed for nuclear reactions, and specifically modified by us for macroscopic applications, are compared with the observations.