Bottles Showing Relative Permeability of Films by Amount of Whiting Formed Within
The Permeability of Paint Films. A series of tests were made to determine the water-excluding values of various combinations of painting pigments ground in pure linseed oil. White pine boards, six inches long, four inches wide, and one inch thick, were carefully prepared and numbered and given three coats of a white paint formula of the corresponding number. After drying, the boards were carefully weighed and immersed in a tub of water for three weeks. After removal, the surfaces of the boards were dried with blotting paper and the boards weighed. The gain in weight, corresponding to the amount of water penetrating through the pores of the wood, was observed. The boards were again immersed and at the end of two months the following results were obtained:
| Formula No. | Grammes of water absorbed through paint | ||||
| 1. | Soya bean oil | 120 | |||
| 2. | Linseed oil | 102 | |||
| 3. | Calcium sulphate | 93 | |||
| 4. | Barytes | 88 | |||
| 5. | Asbestine | 74 | |||
| 6. | Corroded white lead | 59 | |||
| 7. | ⎧ | Basic carb.—White lead | 25% | ⎫ | 58 |
| ⎪ | Basic sulph.—White lead | 20% | ⎪ | ||
| ⎨ | Zinc oxide | 25% | ⎬ | ||
| ⎪ | Calcium sulphate | 25% | ⎪ | ||
| ⎩ | Calcium carbonate | 5% | ⎭ | ||
| 8. | Sublimed white lead | 56 | |||
| 9. | Zinc oxide | 56 | |||
| ⎧ | Zinc lead white | 30% | ⎫ | ||
| ⎪ | Zinc oxide | 40% | ⎪ | ||
| 10. | ⎨ | Basic carb.—White lead | 20% | ⎬ | 42 |
| ⎩ | Calcium carbonate | 10% | ⎭ | ||
| 11. | { | Basic carb.—White lead | 50% | } | 42 |
| Zinc oxide | 50% | ||||
| 12. | ⎧ | Basic carb.—White lead | 38% | ⎫ | 38 |
| ⎨ | Zinc oxide | 48% | ⎬ | ||
| ⎩ | Silica | 14% | ⎭ | ||
The test boards were then exposed, with their content of water, to the action of the sun’s rays. Blistering of the painted surfaces took place in many cases, caused by the rapid withdrawal of the water and its consequent action on the paint film. The tests seem to indicate that a mixture of white lead and zinc oxide, with or without a small percentage of the inert pigments, is not as subject to the action of the water as the single pigment paints. In order, however, to corroborate these tests, it occurred to the writer to develop a more visible means of demonstrating the passage of moisture through paint films.
Bell Jar Apparatus for Testing Permeability of Paint Films
Paint films sealed over mouths of Bottles containing Lime Water. Carbonic Acid Gas generated under Bell Jar passes through Plate Films and precipitates Calcium Carbonate
Another series of white pine boards were therefore soaked in a solution of iron sulphate for several hours. After removal, the surface of each board was dried and coated with one coat of the paints previously tested. After thorough drying for forty-eight hours, there was placed on the surface of each board a few drops of a solution of potassium ferrocyanide. This solution has the effect of producing a blue coloration with iron sulphate, and in every case when it was placed on a paint of considerable porosity, the solution penetrated through and formed a blue coloration beneath the paint. The results corroborated the original tests referred to above.
A series of sheets or films of paints were then prepared according to the method referred to on [page 71]. These films were placed over glass dialyzing cups, allowing the inner surfaces to sag so as to hold a small amount of dilute ammonium chloride solution. Distilled water was placed on the reverse side of the dialyzing apparatus and the tests started. At the end of six days the distilled water in each test was examined and the following results obtained: