THE THEORY AND PRACTICE OF SCIENTIFIC PAINT MAKING =Laws of Paint Making.= To secure a proper comprehension of the composition of paints, and to be able to interpret the functions of their various constituents, requires an understanding of the general physical principles involved. The modern grinder has accepted the Law of Minimum Voids, and upon this law he bases the design of paint formulae, aiming toward the production of what have been properly termed Scientifically Prepared Paints. Perry's formulation of the Law of Minimum Voids in a paint coating, and the analogy which he has drawn between a scientifically prepared paint and a well-proportioned concrete, was the result of genuine scientific thought following observation and experimentation. It must be admitted that analogies are not always safe to draw conclusions from, but it surely is no fallacy in reasoning to draw analogies between these two materials, when they resemble each other in so many ways. To carry out processes of reasoning, and to formulate laws from such close analogies, is certainly a step in the right direction. A graphic summary of the analogies between a properly proportioned concrete and a paint, are shown on next page. Although this table graphically summarizes the principles involved, the matter is presented with greater clearness in the following: Law No. 1--The law of minimum voids to be observed in constructing a paint formula--this law having already been accepted as mathematically correct and technically proved in the technology of concrete and cement. Corollary--The requisite thickness of a paint film together with the utmost attainable strength and impermeability can best be obtained by a properly proportioned blend of pigments of three or more determinate sizes. AN EXHIBITION OF CERTAIN ANALOGIES GOVERNING THE MANUFACTURE OF CONCRETE AND OF PAINT