A series of small glass bottles with wide mouths, holding about two ounces, were half filled with concentrated sulphuric acid, and paint films were tightly sealed over the mouths of the bottles with Canada balsam. The bottles were then carefully labeled, numbered, and accurately weighed upon chemical balances. Later they were exposed under a large glass bell jar containing air saturated with moisture and kept at a constant temperature. The bottles were removed from the receptacle every week and reweighed. The increase in weight, due to the amount of moisture which had penetrated through the films, and absorbed by the sulphuric acid, owing to its hygroscopic nature, was thus determined. In another series of bottles, lumps of calcium chloride were substituted for the sulphuric acid. The results obtained from these tests correspond to those of the former tests, and led to the conclusion that the porosity of linseed oil films varied when different pigments were used in the oil. MOISTURE EXPERIMENTS Figures Given Express Percentage Gain in Weight, e.g., Water Absorbed ==========================+=========+=========+========= | 7 days | 21 days | 49 days --------------------------+---------+---------+--------- White lead and zinc oxide | 0.043% | 0.115% | 0.266% Zinc lead white | 0.049 | 0.130 | 0.284 Red lead | 0.049 | 0.130 | 0.295 Sublimed white lead | 0.049 | 0.128 | 0.292 Zinc chromate | 0.064 | 0.176 | 0.417 Zinc oxide | 0.065 | 0.172 | 0.391 Barytes | 0.074 | 0.202 | 0.466 Willow charcoal | 0.077 | 0.236 | 0.694 Lithopone | 0.083 | 0.228 | 0.550 Chinese blue | 0.092 | 0.276 | 0.671 Natural graphite | 0.104 | 0.350 | 0.951 Ultramarine | 0.119 | 0.336 | 0.814 ==========================+=========+=========+========= Another series of tests was started, in which were used films prepared from various oils and varnishes made especially for the test from different gums. The results of this series are very interesting, as they indicate that certain gums are more powerful than others in making oils resistant to moisture. The reader should study with care the data on treated Chinese wood oil, most excellent results having been obtained when it was used in the proper percentage. EXCLUDING TESTS ON OIL VEHICLES AND VARNISHES SHOWING PERCENTAGE OF MOISTURE ABSORBED AT VARIOUS PERIODS