The problem of the horticulturist in calculating the leaf surface of a fruit tree for measurement of the spray covering is similar to that of the milk plant manager or experimentalist who wishes to determine the amount of water and washing powder required to wash milk bottles of varying sizes. Many factors complicate his problem, chief of which is the fact that usually three sizes of bottles are washed, the total number varying each day, as well as the distribution of sizes. This serves to make any calculation of washing powder only approximate. Other factors, also confusing, are shape of the bottle and thickness of its walls. Displacement calculations may be utilized as a simple method for determination of the volume of glass in a bottle but they are valueless as a measure of the surface area, clue to irregularity in shape. Since both the inside and outside areas of the bottle must be washed it is necessary that both be measured. From these values may be obtained a ratio from which the areas of pint and half-pint bottles may be converted into quart-equivalent area. It would seem logical to calculate amounts of water and washing powder required in washing bottles in terms of the amounts required to wash a quart bottle. In the discussion which follows, the surface areas of three standard size milk bottles have been calculated and the method of calculation given.
