AbstractDimensional analysis was used to simplify an experimental investigation of the relationship between the variables thought to be involved in the retention process. Equipment was developed for applying drops of known size at a range of velocities to glasshouse‐grown barley leaves. This enabled experiments to be carried out to determine the velocity at which drops of a given size were retained on a leaf. Expressions were developed relating the groups of variables thought to affect retention. From these expressions, a graph was produced which can be used to predict the retention behaviour over the experimental range investigated. For example, if drops (100‐400 μm diameter) of water containing a surfactant are applied at their terminal velocitres to the leaves, it is predicted that (a) smaller drops will be retained better than larger drops, and (b) larger drops will be retained if the surface tension of the spray liquid is red
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