Coalescence and fragmentation of equal and unequal liquid-drop pairs a
re studied using a new experimental technique in which mercury drops c
ollide while sliding on a horizontal glass surface. The limits for coa
lescence 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 fra
gmentation residues. The predictions of various models, including a dy
namic theory originally developed for nuclear reactions, and specifica
lly modified by us for macroscopic applications, are compared with the
observations.