The Kozeny equation of laminar flow through granular materials is extended to the transition region by means of a chart of the friction factor versus the Reynolds number. A chart of the backwashing number versus the Reynolds number is developed for estimating wash rates required at impending suspension and during suspension of filter grains. The friction factor during backwash decreases greatly at porosities greater than approximately 0.6. Small floc particles deposit in a filter, as a sheath, around the sand grains. A chart for the easy computation of the deposit ratio from the sand size and hydraulic gradient is presented. The rate of removal for a given volumetric concentration of floc in the water at each depth is found to decrease greatly with depth. This decrease in effectiveness is related to the adhesiveness of the floc to the sand.

A critical evaluation of population forecasting techniques currently (1964) used by sanitary engineers is presented. Methods for estimating population are reviewed and sources of population statistics are outlined. Graphical (plotting) methods, mathematical or formula methods, statistical methods of correlation and regression analysis, ratio methods using other estimates or forecasts, component methods based on the analysis of growth composition (births, deaths, migration), and methods based on economic forecasts, particularly those of future employment, are described. The relative accuracy of various methods is reviewed, and improvements in current sanitary engineering methodology are suggested, including the adoption of more analytical forecasting techniques.

An analysis is made of the displacement and attenuation in a acoustic field with suspended particles to provide the theoretical basis of the experimental determination of the size and concentration of the particles in air pollution. The theory is valid for a particle larger than the mean free path of both components of the mixture and is compared favorably with the existing experimental data. The result shows that a pollution counter could be designed using acoustic properties.