240 The Philippine Journal of Science 1917 



Table III. — Effect of age upon the strength of oil-silica films. 



The films after sixty days were tacky and soft and of greatly 

 reduced tensile strength. 



To study the effect of age upon the strength of paint films 

 prepared from active pigments, red lead was employed. The 

 paints were prepared by incorporating 40 grams of red lead with 

 25 grams of oil, and the films were the same in weight as the oil- 

 silica films previously described. Table IV shows the relation 

 between the increase of strength and the age of the paint films. 



Table IV. — Tensile strength of red lead paint films. 



I Breaking strength in terms of 

 I centimeters of mercury. i 



Stretches in centimeters. 



Age of film in days. 



Linseed 1 



Do I 



Lumbang bato 



Do _ ... 



18.9 



16.1 



50,1 

 100 10.7 



Age of film in days. 

 . __ _ 



40. 



0. 22 I 0. 18 ' 0. 18 



0.26 ! 0.24 | 0.26 0.24 



Table IV shows that the paint films attained their maximum 

 strength between the third and the fourth month and that then 

 a gradual decrease followed. 



Further tests were conducted to compare the paint properties 

 of lumbang banucalag with those of linseed oil and lumbang bato 

 oil. Twenty-five grams of lumbang banucalag oil were mixed 

 with 40 grams of red lead ; the mixture became thick and pasty in 

 fifteen minutes, a property by means of which it can be differen- 

 tiated from lumbang bato, because the latter, very much like 



