346 REPORT ON NATIONAL MUSEUM, 1886. 



outset that the i^roblem of ascertaining by laboratory or other tests 

 the actual qualities, good or bad, of any stone, is peculiarly complicated 

 and difficult.* In the present state of our knowledge nothing like 

 definite rules of procedure with any probability of accurate and reliable 

 results can be given. That the difficulties may be better appreciated 

 it may be well to note here the main points to be considered. In the 

 order of their apparent importance they are: 



(1) Resistance to changes in temperature. 



(2) Resistance to chemical action of the atmosphere. 



(3) Crushing strength and elasticity. 



(4) Resistance to abrasive action of feet and wind-blown sand. 



The order as above given maybe subject to modification to suit indi- 

 vidual cases. In many instances the actual strength of a stone is a 

 matter of little importance, and in protected situations the quality men- 

 tioned under (4) may be wholly left out of consideration. In still other 

 cases, as in bridge abutments, strength and elasticity are matters, of 

 greatest import, while that of change of color can have no essential 

 value. In the arrangement given above, especial regard has been had 

 to stone exposed in the exterior walls of a building, and in a varied 

 climate like that of the northern and eastern United States. 



The first item for consideration is then the matter of climate. This, 

 together with the location in which a structure is to be erected, with 

 especial reference to proximity to large cities and manufacturing estab- 

 lishments, and even the directions of the prevailing winds and storms, 

 are of primary importance and need consideration as well as do the 

 physical and chemical properties of the stone itself.f 



Our [Northern and Eastern States, with an annual precipitation of some 

 thirty-nine or forty inches and a variation in temperature amounting in 

 some cases to not less than 120°, are necessarily more trying than those 

 where the precipitation is less or the tenrperature more uniform. There 

 is many a porous sand or lime stone wdiich could endure an exposure of 



* See article " On the testing of building-stone," by the writer in American Archi- 

 tect for February 16, 1889. 



t "As an instance of the difference in degree of durability in the same material sub- 

 ject to the effects of atmosphere in town and country we may notice the several 

 frustra of columns and other blocks of stone that were quarried at the time of the 

 erection of St. Paul's Cathedral in London, and which are now lying in the island of 

 Portland, near the quarries from where they were obtained. These blocks are in- 

 variably found to be covered with lichens, and although they have been exposed to 

 the vicissitudes of a marine atmosphere for more than one hundred and fifty years 

 they still exhibit beneath the lichens their original forms, even to the marks of the 

 cbisel employed upon them, whilst the stone which was taken from the same quarries 

 and placed in the cathedral itself is in those parts which are exposed to the south 

 and southeast winds found in some instances to be fast moldering away." (Gwylt's 

 Encyclop. of Arch., p. 458.) 



It is stated that in England the northern part of a building is always in a better 

 state of preservation than the southern, owing to the more uniform amount of moist- 

 ure and less heat from the sun. 



