Corollary C--It follows directly that the thickness of a paint coating is determined by the particles of pigments having the largest characteristic size, even if that pigment be present only in moderate percentage. Upon this principle depends the comparatively great thickness of film and moderate spreading rate of paints composed of such pigments as basic carbonate--white lead, red lead, barytes, etc., and the strongly contrasted thinness of film and high spreading rate of paints composed of the sublimated pigments such as lamp black, zinc oxide, basic sulphate--white lead, zinc-lead white, leaded zinc, etc. In commenting upon the announced laws set forth above, Heckel says: "The recognition of these laws was an exercise of pure deduction. Paint manufacturers before Mr. Perry's announcement were producing paints containing three or more pigments with particles of varying characteristic sizes; but their procedure was based largely on empirical knowledge, the result of accumulated experience, due to a conscientious endeavor to produce the highest type of paints for economic service. In the absence of any law to govern or to limit the use of the reinforcing pigments, inexperienced manufacturers had brought upon the market paints which were badly proportioned as to the several pigments, or burdened beyond the limits of effectiveness with reinforcing pigments. To all paint manufacturers Perry rendered a substantial service in deducing for them the laws set forth in his address. In the results following a recognition of these laws there was nothing new or startling, but Perry was the first to give the principles from which it can be determined in advance whether a paint formula will prove to be physically good or bad in practice. [Illustration: Series of Paint Chasers, Mixers, and Grinders] [Illustration: Overhead Churn Mixer] [Illustration: Battery of Paint Mixers and Grinders of Modern Underdriven Type] [Illustration: _Photographs courtesy of Ernest Heath_ View showing Shrinkage in Bulk of Paint Pigment after being ground in Oil. Filled Barrel on Right with the Oil forms one-third Barrel Paste as shown in Barrel on Left] [Illustration: View showing careful Dressing of Bull Stone Mill from Grinder]