334 



fortunately this can not at all times of the year and in all places be 

 done, and artificial methods must be resorted to. Brard's process, as 

 modified by M. Hericart and Thury, consisted in boiling the cube to be 

 experimented upon for half an hour in a saturated solution of sulphate 

 of soda (Glauber salt) and then allowing it to dry, when the salt taken 

 into the pores crystallized and expanded in a manner supposedly some- 

 what similar to that of water when freezing.* 



This process is not now in general use, as experiment has shown that 

 the salt exercised a chemical as well as mechanical action, and produces 

 results somewhat at variance with that of freezing water. The most 

 important series of experiments ever performed with the process in 

 this country were those of Mr. 0. G-. Page, made with reference to the 

 selection of material for the Smithsonian Institution Building at Wash- 

 ington. 



The results are given in the following tablet 



Materials. 



Marble, close-grained, Maryland 



Marble, coarae "alum stone," Baltimore County, Mil 



Marble, blue, Maryland 



Sandstone, coarse, Portland, Conn 



Sandstone, lino, Port land, Conn 



Sandstone, red. Seneca Creek, Md 



Sandstone, dove-colored, Seneoa Creek, Md 



Sandstone, Little Falls, N. J 



Sandstone, Little Falls, X. J 



Sandstone, coar.se, X ova Scotia 



Sandstone, dark, coarse, Seneca Aqueduct, Peters' 8 quarry. 



Sandstone, Acqo.ia Creek, Va 



Sandstone, 4 miles above Peters's quarry, Md 



Sandstone, Beaver Dam quarry, Md ' 



Granite, Port Deposit, Md 



Marble, close-grained, Montgomery County, Pa 



Limestone, blue, Montgomery County, Pa 



Granite, Great Falls oi" the Potomac 



Soft brick .- 



Hard brick 



Marble, coarse dolomite, Mount Pleasant, X. Y 



Specific 

 gravity. 



2. k:w 

 2. 857 

 2. «13 



2. 583 



2. G72 

 2. 486 



2. 482 

 2. 518 



2. 230 



2. CO!) 

 2. 727 

 2. G9i> 



2.211 

 2. 291 

 2. 8G0 



Loss in 

 grains. 



0.19 

 0.50 

 o. 34 



14.36 



24. 93 

 0.70 

 1.78 

 1.58 

 0.G2 

 2. 16 

 5. GO 



18. GO 

 1.58 

 1.72 

 5.05 

 0.35 

 0.28 

 0.35 



1G.46 

 1.07 

 0.91 



The specimens operated upon, it should be stated, were cut in the form 

 of inch cubes. Each was immersed for half an hour in the boiling 

 solution of sulphate of soda, and then hung up to dry, this perform- 

 ance being repeated daily throughout the four weeks which the exper- 

 iment lasted. 



The injurious effects of artificial heat, such as is produced by a burn- 

 ing building, are, of course, greater in proportion as the temperature is 

 higher. Unfortunately sufficient and reliable data are not at hand for 

 estimating accurately the comparative enduring powers of various 

 stones under these trying circumstances. It seems, however, to be well 

 proven that of all stones granite is the least fire-proof, while the fact 

 that certain of the fine-grained siliceous sandstones are used for furnace 



* Chateau, Technologie Du Iiatiment, Vol. I, p. 262. 



tFrorn Hints cm Public Architecture by Robert Dale Owen, p. 119, 



