BUILDING AND ORNAMENTAL STONES. 331 



one hand and driven by the hand-hammer (Fig. 5), used in making holes 

 for " plug and feather' 7 splitting and other light work. 



Grub' saic. — A saw for cutting stone by hand. It consists of a plate 

 of soft iron from one-twentieth to one-tenth of an inch in thickness and 

 from C> inches to 4 feet in length ; the blade is notched on the lower edge 

 and fitted with a wooden back for convenience in handling and to pre- 

 vent bending. Sand or emery is the cutting material, as with the steam 

 saws (Fig. 17, PI. V). 



H.— THE WEATHEBING OF BUILDING STONES. 



The term weathering, as applied to stone, includes the series of phys- 

 ical changes induced by alternations of heat and cold, or by friction, as 

 well as the more complex series of chemical changes, such as may be 

 comprised under the heads of oxidation, deoxidation, hydration, and 

 solution. Since a stone exposed in the walls of a building may be sub- 

 jected to the influence of any one or the combined influences of several 

 of these agencies, whereby serious consequences, as of discoloration or 

 disintegration may result, it is important to consider, in more or less 

 detail, their comparative energies under varying conditions and upon 

 the various kinds of stone commonly employed for structural purposes. 



(1) PHYSICAL AGENCIES. 



Heat and cold. — It is safe to say that none of the conditions under 

 which a stone is commonly placed are more trying than those presented 

 by the ordinary changes of temperature in a climate like that of our 

 Northern and Eastern States. Stones, as a rule, possess but a low con- 

 ducting power and slight elasticity. They are aggregates of minerals, 

 more or less closely cohering, each of which possesses degrees of ex- 

 pansion and contraction of its own. In the crystalline rocks these dis- 

 similar elements are practically in actual contact ; in the sandstones 

 they are removed from one another by a slight space occupied wholly 

 or in part by a ferruginous, calcareous or siliceous cement. As tem- 

 peratures rise, each and every constituent expands more or less, crowd- 

 ing with resistless force against its neighbor ; as the temperatures 

 decrease a corresponding contraction takes place. Since with us the 

 temperatures are ever changing, and within a space of even twenty-four 

 hours may vary as much as forty degrees, so within the mass of the 

 stone there is continual movement among its particles. Slight as these 

 movements may be they can but be conducive of one result, a slow and 

 gradual weakening and disintegration. 



This constant expansion and contraction is often sufficient in amount 

 to be appreciable in stone structures of considerable size. Thus Bunker 

 Hill Monument, a hollow granite obelisk, 221 feet high by 30 feet square 

 at the base, swings from side to side with the progress of the sun during 



