406 Introduction to the Study of Science 



some mineral such as white lead, zinc white, and litharge. 

 Creosote is a product derived from coal tar. Where appear- 

 ance is considered in dwellings and other buildings, paint is 

 used. Tar and creosote are used to preserve piles, telegraph 

 poles, railroad ties, and shingles. 



II. STONE 



192. Properties of building stone. Among the materials 

 commonly used in building and construction are the various 

 kinds of rock or stone. About $80,000,000 worth of stone is 

 used in this country in a year. Of the many kinds of rock used 

 in building there are several distinct classes which have different 

 qualities. Some are comparatively easy to cut and shape, but 

 do not take a high polish. Of these, sandstone and slate are 

 common examples. Other kinds, such as marble, are very 

 heavy or hard, capable of taking on a high polish, and are used 

 largely for ornamentation in buildings. Still others, as granite, 

 are very hard, with gleaming crystals of beautiful colorings in 

 their texture. 



Durability is an important factor in stone used for building 

 purposes. The climate of the northeastern part of the country 

 is especially destructive to stone. Cleopatra's Needle, which 

 had stood in the dry climate of the Nile Valley for more than 

 eighteen centuries without showing greatly the effect of weather, 

 quickly began to disintegrate after it was placed in Central 

 Park, New York. It is now protected with a coating of paraffin. 

 The following table shows the length of time stones can remain 

 exposed to the weather in New York City and vicinity before 

 their surfaces begin to crumble or flake off. 



Brownstone (fine and compact) 100 to 200 years 



Sandstone (best quality) 100 years to many centuries 



Granite 75 to 200 years 



Limestone 20 to 40 years 



Marble (fine) . 50 to 100 years 



Gneiss 50 years to many centuries 



