rl50 



NEW YORK STATE MUSEUM 



to the sun and atmosphere. The sea green slate fades unevenly; 

 after a year's exposure as many as six different shades of color 

 appear. The other colors all fade somewhat, but, if the slates 

 are well matched, the change of color is fairly uniform and 

 passes unnoticed. 



1 " A specimen of the red roofing slate of Washington county 

 was tested and found to have a specific gravity of 2.84, equivalent 

 to a weight of 177 pounds a cubic foot. It contained 1.87$ of 

 ferrous oxid, and 7.36^ of ferric oxid. Its absorptive percentage 

 was .15. It lost .07^ in weight in the sulfuric acid solution test. 

 It remained unchanged in tests of alternate freezing and 

 thawing." 



^mock, J: C. Building stone in New York. N. Y. state mus. Bui. 10. 

 v. 2. p. 281. 



