ART OP BUILDING. 243 



heres to the stones or bricks, as well as the adhesion of its 

 own particles. These forces are greatly augmented by age. 

 The following table shows the force with which stone 

 and brick adhere together, when joined by good mortar 

 made of nine parts of sand and one of good lime. 



Two pieces of Maine granite, hewn, 105 pounds. 

 The same not hewn, ... 162 

 Red sandstone, hewn, - - 159 



The same not hewn, - - - 166 

 Sienite, (Quincy) hewn, - - 101 

 The same not hewn, - 147 



Boston unpressed brick, - - 172 

 ditto pressed. - - - - 167 

 These had all been united nine months, and placed in a 

 dry situation. 



The following appears to be the principle on which 

 mortar acts as a cement in joining masonry. It is well 

 known that when quicklime and water are mixed together,, 

 the lime swells and falls to pieces, and is soon reduced to a 

 fine powder, and so much heat is produced as to convert 

 a part of the water into steam. If the lime be weighed 

 after being slacked, it will be found to have increased in 

 weight, which is owing to a part of the water having com- 

 bined with the lime and become solid ; of course, the 

 water has parted with that portion of its heat which 

 caused its fluidity; hence, the great heat produced in 

 slacking lime for if two parts of powdered quicklime 

 and one part of powdered ice (both at 32 of the thermome- 

 ter) be mixed together, they instantly combine and their 

 temperature is 212. Here the increase of heat comes 

 from the ice. When large quantities of lime are slacked, 

 heat and light are produced in large quantities hence 

 the reason vessels and buildings filled with lime are often 

 set on fire by the water getting to it. This combination 

 of lime and water, is called a hydrate of lime. 



When the hydrate of lime is forming, if the black ox- 

 ide of iron, or the scales ^thrown from it when hammered 

 by the smith, be mixed -with burnt clay or sand, the 

 mixture becomes harder than the lime would alone, which 

 is owing to a certain degree of chemical attraction be- 

 tween the hydrate of lime and these substances. 



