STRUCTURAL PAINT TESTS 231 



the report. No reductions were made to any of the paints 

 applied except in three cases, where the viscosity was so great 

 that it was necessary to add a small amount of pure spirits of 

 turpentine. The amount of paint was proportionately increased 

 in such cases, so that the evaporation of the turpentine would 

 leave upon the plate the amount of paint originally intended. 



The appearance of the completed series of test panels is shown 

 on page 221. 



Vehicles Used and Reasons for Avoidance of Japan Driers. 

 The pigments used were selected with the view to securing as 

 nearly as possible purity and strength, and as already noted, 

 were out of the same lots used in making the preliminary labora- 

 tory tests on inhibitives. They were ground in a vehicle com- 

 posed of two parts of raw linseed oil and one part of pure boiled 

 oil. Paint is generally caused to dry rapidly by the use of japan 

 or driers. These materials contain a large amount of metallic 

 oxides which might have some effect in either exciting or retard- 

 ing corrosion. To prevent the introduction of such a factor, 

 these materials were not used in the test. The boiled oil, with 

 its small percentages of metallic oxides, was sufficient, however, 

 to cause the paints to dry in a short time after they were spread. 



Testing Effect of Various Prime Coats. Some of the special 

 tests made included a series of plates prime-coated with differ-' 

 ent inhibitive pigments, and these tests were designed to deter- 

 mine which pigments offer the best results for such work. These 

 plates were all second-coated with the same paint. It is the 

 opinion of the authors that any good excluding paint may be 

 used whether it be inhibitive in action or not, provided the con- 

 tact coat is inhibitive. If, however, both coats can be designed 

 so as to have the maximum possible value from both these points 

 of view, the best results would, of course, accrue. The only way 

 such data can be obtained is by careful observation of the results 

 of exposure tests. 



Combination Formulas Tested. By selecting a series of pig- 

 ments which in the water tests showed inhibitive tendencies, and 

 properly combining these pigments into a paint, it was thought 

 possible that a more or less inhibitive paint would be produced. 

 If this proved to be the case, it would follow that the selection 

 and introduction into a paint of the stimulative pigments would 

 inevitably produce a paint unfit for use on iron or steel. 



