556 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



the chairman's desk were pressed with a pressure of 250 tons, 

 and that they were harder than the ordinary burnt porcelain. 



The Chairman. — Can we make a step forward so as to guard 

 our buildings by making bricks impervious to water ? We have 

 learned to make mortar more perfect within this last five years. 

 This improvement consists in properly sifting the sand, then 

 adding a finer sand, and after that the lime in such a state as to 

 enable it to surround every particle of the sand. Mortar made 

 rightly, and applied in a thin coat is an imperishable substance. 

 If we can make bricks entirely impervious to water they will be 

 better than stone. 



Mr. Johnson said that in London the tiles were glazed, and 

 that the outer surface of the bricks are glazed in Brighton, Eng- 

 land. 



A Visitor.— Such a brick as that was made in the Bennington 

 pottery. 



The Chairman stated that that pottery had failed long since. 



Mr. Garvey. — No face to a wall would be better than a surface 

 of mortar. If magnesian lime is selected you cannot accomplish 

 anything. Well burnt bricks should be well saturated and free 

 from dust before being used, and then by covering them with a 

 coat of mortar they would last for ever. 



Dr. Knight presented several samples of Silexian marble, and 

 said : 



This is a compound, the base of which is lime. It was intro- 

 duced into this city in 1852, by an Englishman. Kean's cement 

 is used in the manufacturing of it. The patent for it was dis- 

 posed of, for use in this city, for $5,000. It will bear more heat 

 than marble, and you can make a shelf of it very thin and still 

 it will bear to be carried by two men, one at each end, which is 

 not the case with marble. Mr. Sherwood of Greenwich, Connec- 

 ticut, is now manufacturing it. The only fault it has is, that it 

 cannot be made to pay the manufacturer. It requires four hours 

 to have it set without any heat. 



The Chairman. — How does it bear the fire ? 



Dr. Knight. — Much better than marble. 



Mr. Stetson. — Is Kean's cement used all through the mass, or 

 only on the surface ? 



Dr. Knight. — It is used all through it. The middle is made of 

 the same material, only coarser. 



Mr. Johnson. — Will it retain moisture ? 



