On the basis of the theory of capillarity, the process of formation of a wetting perimeter when a spherical particle touches a planar liquid surface is analysed taking into account the line energy of this perimeter. The minimum size of particle which can float is calculated and an accurate estimate is made for the minimum time of touching of particle and surface. The kinetic energy of collision between an air bubble and the particles is used to calculate the maximum size of particles which can remain attached for flotation. Flotation data suggest that a lower limit for the size of isolated particles which can be floated is of the order of 1 µm and a comparison of this radius with the theoretical limit gives a value of 10^–4 to 10^–5 dyn for the line energy of the wetting perimeter. Predictions of the flotation region in terms of particle size and contact angle using this energy do not conflict with practical findings.