306 SCIENCE IN SHORT CHAPTERS. 



ineable to water so long as they are free from any chemical 

 decomposition of their" feldspathic constituents; but when 

 we come to sandstones and limestones, or intermediate ma- 

 terial,, very wide differences prevail. 



The possible width of this difference is shown in the 

 behavior of the unselected material in its natural home. 

 Certain cliffs and mountains have stood for countless ages 

 almost unchanged by the action of frost; others are break- 

 ing up with attonishing rapidity in spite .of apparent solid- 

 ity of structure. The Matterhorn, or Mont Cervin, one of 

 the most gigantic of the giant Alps, 15,200 feet high, is 

 rendered especially 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 awhile 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 prac- 

 tical 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 wherever 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 con- 

 structing a building and watching the result, is very de- 

 sirable. The subject of testing building materials in spe- 

 cial reference to their resistance of frost was brought be- 

 fore 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 ex- 

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

 to the action of freezing mixtures. Afterwards he found 

 ihat by availing himself of the expansive force which cer- 



