THE ACTION OF FROST Itf WATER-PIPES. 35 



Building stones are so various both in chemical composition 

 and mechanical structure that the action of freezing water is 

 necessarily as varied as the nature of the material. The highly 

 silicious granites (or, rather, porphyries that commonly bear the 

 name of granite) are practically impermeable to water so long 

 as they are free from any chemical decomposition of their 

 f eldspathic constituents ; but when we come to sandstones and 

 limestones, or intermediate material, very wide differences 

 prevail. 



The possible width of this difference is shown in the 

 behavior of the unselected material in its natural home. Cer- 

 tain cliffs and mountains have stood for countless ages almost 

 unchanged by the action of frost ; others are breaking up with 

 astonishing rapidity in spite of apparent solidity of structure. 

 The Matterhorn, or Mount Cervin, one of the most gigantic of 

 the giant Alps, 15,200 feet high, is rendered especial^ 

 dangerous to ambitious climbers by the continual crashing 

 down of fragments that are loosened when the summer sun 

 melts the ice that first separated and then for a while held them 

 in their original places. All the glaciers of the Alps are more 

 or less streaked with " moraines/' which are fragments of the 

 mountains that freezing water has detached. 



Our stone buildings would suffer proportionally if some 

 selection of material were not made. Generally speaking, this 

 selection is based upon the experience of previous practical 

 trials. Certain quarries are known to have supplied good 

 material of a certain character, and this quarry has, therefore, 

 a reputation which is usually of no small value to its fortunate 

 owner. Other quarries are opened in the neighborhood wher- 

 ever the rock resembles that of the tested quarry. 



Sometimes, however, materials are open for selection that 

 have not been so well tested, and a method of testing which is 

 more expeditious and less expensive than constructing a building 

 and watching the result, is very desirable. The subject of 

 testing building materials in special reference to their resist- 

 ance of frost was brought before the Academy of Science of 

 Paris by M. Brard some years since. 



In his preliminary experiments he used small cubes of the 

 stone to be tested, soaked them in water, and then exposed 

 them to the air in frosty weather, or subjected them to the 

 action of freezing mixtures. Afterward he found that by avail- 

 ing himself of the expansive force which certain saline solutions 

 exert at the moment of crystallization, he could conveniently 



