AMERICAN INSTITUTE. 463 



it 600 feet thick. It contains an appreciable amount of lime, and its color 

 is due to iron and mica. By their combination it receives a beautiful life- 

 like color. This quarry is in the county of Union. 



Athens marble has a beautiful cream color superior to that of caen stone. 

 It is a Silurian limestone, is easily worked, and resists an immense pros- 

 sure. It is a compact marble, that is, does not show any crystaline struc- 

 ture. 



. The sandstones of the Western States are characterized by the ease with 

 which they disintegrate. 



Professor Ileuben. — We have many causes of disintegration, air, water, 

 frost, mosses, lichens, &c. Mosses and lichens are the forerunners of all 

 soils, we may judge then of the liability of stones to disintegrate by ascer- 

 taining how much mgisture they will absorb, how they will be acted upon 

 by frost, or by the analogous process of crystalizing souet salt from a solu- 

 tion ; and lastly, by the ease with which lichens and mosses attach them- 

 selves to exposed parts of the rock. 



Mr. Stetson asked if the amount of absorption of water measured the 

 liability to disintegration. There is a stone in Connecticut upon which 

 some one, a long time since, painted some letters which are now in relief 

 evidently from the wasting away of the unprotected stone. 



Dr. Jackson. — Water does not enter marble. It requires an immense 

 pressure to force it in. 



Mr. Tillman. — The expansive action of water while freezing, is the prin- 

 cipal cause of disintegration. Water freezing in holes in rocks will split 

 them. 



Professor Reuben. — It will be well to bear in mind that water does not 

 freeze as easily under pressure as otherwise. Pressure lowers the freezing 

 point, and the cohesion of the particles of stone maybe sufficient to prevent 

 the water freezing at the temperature of severest winter. 



Dr. Vanderweyde. — With cohesion sufficient, and a porous structure, 

 the water should force out through the pores in freezing without either 

 splitting or disintegrating the stone. This may occur with some stones — 

 certainly not with all. 



The hour for adjournment having arrived, " The Telegraph " was selected 

 as the subject for next evening, after which the Association adjourned. 



Polytechnic Association op the American Institute, ) 



Septe/nber 22d, 1859. } 



Professor Mason, Chairman. John Johnson, Esq., Secretary, pro tem. 



Mr. Garvey asked for the continuation of the report of the Committee on 

 Building Materials. 



Prof. Mason. — It has not yet been completed. 



Mr. Garvey. — Pulverized flints are sometimes used with lime in making 

 mortar, and experienced builders always employ a good sharp silicious 

 sand. This seems to indicate that a chemical action takes place between 

 the lime and silex. 



