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The object of the investigation was to find hydrophobic materials which could be applied to the surface of the leather to replace the fats and greases ordinarily used. Silicones, described above, and synthetic rubbers such as those made from methacrylates, polybutadiene, and similar materials, were considered most satisfactory. The silicones were applied by impregnating the leather with organic solvent solutions of the material and the excess solvent was removed by drying; the resulting surface is resistant toward superficial wetting.

The largest part of the market for rainw and for umbrellas is in water-repellent fabr: which have been treated with hydrophobic chei cals that make the water collect in drops and i off without penetrating the cloth. Usually 1 water-repellent chemical is deposited on in vidual fibers in an extremely thin waxlike film that the spaces between yarns and fibers remi essentially unchanged and, consequently, venti tion is unimpaired.

The term "waterproofing" is usually used to designate the high resistance of a material to the passage of water under dynamic conditions, achieved by coating it and filling its larger pores with an impervious substance. Water "repellency," on the other hand, is usually obtained by applying chemicals that resist wetting, or by tight weaving, or both; in both instances, hydrophobic surfaces are produced which do not change the original texture or porosity of the material. This applies primarily to textiles.