HIYSICAL LABORATORY PAINT TESTS 



83 



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 bal- 

 ances. Later they were exposed under a large glass bell jar con- 

 taining 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 lin- 

 seed oil films varied when different pigments were used in the oil. 



MOISTURE EXPERIMENTS 

 Figures Given Express Percentage Gain in Weight, e.g., Water Absorbed 



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. 



