274 TOWERS AND TANKS FOR WATER-WORKS. 



twelve hours each day, and ordinary atmospheric air for the 

 remaining twelve hours, the test to be continued for thirty days. 



" The porosity is determined by noting the absorption of a 

 drop of oil on the coating. If the film is impervious, the drop 

 of oil will run down the panel in a narrow band the width of the 

 original drop, 1 but if the life of the coating has been destroyed 

 the drop of oil will spread out to a more or less greasy blotch, 

 depending on extent of disintegration. 



" The glass panels are tested for water-repellent properties 

 by treating the dried coating with a few drops of water. Evap- 

 oration is prevented by means of a cover-glass, and the coating 

 examined after the water has been in contact for twelve hours. 



" The capacity of the coating to withstand destructive agencies 

 necessary to equipment and maintenance of structure will require 

 special tests. 



" For steel cars and bridges the coating on glass is tested with 

 lubricating arid burning oils to determine if it is disintegrated. 

 For refrigeratihg-cars it is tested in the same manner with a 

 common salt solution. 



" A further set of laboratory tests are made by coating saucers 

 of sheet iron 8 inches diameter i inch deep with two coats of 

 paint. These saucers are filled with ordinary tap water and 

 allowed to evaporate under cover to dryness, the water renewed 

 until definite conclusions can be deduced. 



" Chemical analyses of the coatings will also be made to deter- 

 mine percentage of pigment, oil, and volatile matter, with com- 

 position and quality of each. 



" The above service and laboratory tests are to be conducted 

 at as widely distant points and under as different conditions as 

 possible. The service tests are to be carefully examined at 

 stated intervals and the entire series of experiments accurately 

 tabulated for comparsion with the long-time service tests. 



" From these data it is expected that laboratory tests can be 



