590 REPORTS OF THE BUILDING COMMITTEE. 



found in quarries close to the line of the Chesapeake and Ohio canal, is the hest and 

 most durable of all the Potomac freestones. 



The lilac-gray variety found in the Bull Run quarry, twenty-three miles from 

 "Washington, was especially recommended, and pronounced to be equal, if not supe- 

 rior, to that supplied for Trinity church, New York, from the quarries of New 

 Jersey. 



In regard to this latter material, it was stated that it possessed a quality that should 

 especially recommend it to the attention of builders. When first quarried it is com- 

 paratively soft, working freely before the chisel and hammer ; but by exposure it 

 gradually indurates, and ultimately acquires a toughness and consistency that not 

 only enables it to resist atmospheric vicissitudes, but even the most severe mechanical 

 wear and tear. Thus, on the tow-path of the aqueduct, near Seneca creek, over 

 which horses and mules have been travelling almost daily for upwards of twenty 

 years, this freestone was found still unimpaired. Even the corners around which 

 the heavy lock-gates swing, showed no signs of chipping or decay ; and on the per- 

 pendicular wall of the aqueduct, where the water is continually oozing through the 

 joints and trickling down its face, forming an incrustation of carbonate of lime, this 

 freestone was observed, where the calcareous crust had scaled off, with the grooves 

 and ridges of the surface still nearly as distinct as when the blocks first came from 

 the hands of the stone-mason, more than twenty years ago. 



The rare and valuable quality possessed by this freestone, of hardening by expo- 

 sure to the weather, and which may be due to iron in its composition, passing from 

 a lower to a higher degree of oxidation, is occasionally found in building stone on 

 the continent of Europe ; as, for example, in a calcareous freestone which has been 

 excavated for centuries from St. Peter's mountain, near Maestrich, in Belgium. It 

 is highly prized wherever found, as this peculiarity permits the freestfone to be 

 wrought at considerably less expense than either granite or marble, and imparts to it 

 a durability increasing with age. 



Further to test the durability of these various building materials under exposure 

 to the vicissitudes of the seasons, specimens of each, and also of other building stones 

 from New York and elsewhere, were handed to a gentleman, of this city, experi- 

 enced in chemistry, and, having a laboratory at command, he was requested to 

 subject these to a process recommended by Brard, a French chemist, and described in 

 the " Annales de Chimie et Physique;" according to which, the crystallization of 

 the sulphate of soda is substituted for the freezing of water ; and thus, by artificial 

 means, the action of the elements on these materials — the alternate freezing and 

 thawing to which the external component of a building is in this climate annually 

 subjected — is in a measure imitated. The result — which, however, in consequence of 

 the short time which could be allowed for the process, must be considered an approx- 

 imation only to the truth — is given in a report from the gentleman in question The 

 specimens were reduced to inch cubes ; and it was found, after four weeks, that a 

 cube of granite had lost about one-third of a grain; a cube of the fine grained mar- 

 ble, about one-fifth of a grain; a cube of the best quality of the "alum-stone," or 

 coarser-grained marble, half a grain to a grain and a half; and a cube of freestone 

 from the Patent Ofiice, which, however, was judged not to be a fair average speci- 

 men of the Aquia creek freestones, lost eigliteen grains and a half. Freestone from 

 Trinity church lost from two-thirds of a grain to about a grain and a half. The 

 brown Connecticut stone, freely used in New York, lost from fourteen to nearly 

 twenty-five grains. Coarse-grained New York marble, from Mount Pleasant, lost 

 nearly a grain ; Nova Scotia coarse-grained sandstone, about two grains; while Penn- 

 sylvania blue limestone lost little over a quarter of a grain. 



As to the relative cost of the Maryland granite, Maryland marble, fine-grained 

 and coarse-grained, Aquia creek freestone, and Seneca creek freestone, it was found, 

 from the report of the geologist and from actual offers made to the committee by 

 owners of quarries, and which will be found recorded iD the journal of the commit- 

 tee, to be, per cubic foot of dimension stone delivered in Washington, as follows : 



1st. For coarse-grained marble with large crystals, commonly called "alum stone," 

 from fifty to sixty cents, according to quality. 



2d. For fine-grained marble the lowest offer was seventy cents. 



3d. For granite, forty-six cents. 



4th. For Aquia creek freestone, forty cents. The materal used in the public build- 

 ings in Washington, in blocks of ordinary size, has cost from forty to fifty cents. 



5th. For Seneca freestone, the lilac-gray variety, from Bull Run quarry, twenty 

 cents. A contract has been made by a gentleman of Washington, not connected 



