218 [Assembly 



amount and degree of this growth varies with position in reference to 

 the sun, and with a more or less elevated situation. 



It should not be forgotten, however, that any stone giving root to 

 lichens is not one of those which most easily disintegrate ; for in these 

 the destruction goes on so rapidly, that the surface does not allow the 

 growth of such plants. The lichen-covered rocks in nature are usually 

 those of great strength and durability. None of the softer or rapidly 

 • decaying rocks produce this vegetation. 



4. The solvent action of loater is never so great upon artificial struc- 

 tures, as upon the rock in its natural position; for in the latter case, 

 it is usually aided by a covering of soil, through which tlie water is 

 filtered; and if not thus covered, the rock is exposed in broad surfaces 

 to much greater action than in the walls of a building. 



5. The oxidizing influence of the suji's rays is only considerable when 

 aided by moisture, and in this condition scarcely operates except upon 

 iron pyrites and iron in a low state of oxidation. 



6. The effect of electricity. Prof. Henry, after citing the effects pro- 

 duced by water charged with carbonic acid, says: "Again, every flash 

 of lightning not only generates nitric acid — which, in solution in the 

 rain, acts upon the marble — but also by its inductive effects at a dis- 

 tance, produces chemical changes along the moist wall, which at the 

 present time are beyond our means of estimating." 



7. Effects from sulphurous gases 2iroduced by burning coals. In the 

 unexpected gradual dilapidation of the New Houses of Parliament in 

 London, the causes have been sought and apparently found in an 

 agent heretofore little regarded as one producing serious deterioration 

 of buildings. The stone is a magnesian limestone from Bolsover moor, 

 and was selected as having been found to retain its integrity and to 

 have preserved in a very perfect degree some of the carvings in South- 

 well church through a long period of time. 



The same material, and from the same locality as stated, has been 

 used in London with a very different result. An examination made a 

 few years since led to the belief that this disintegration of the stone was 

 caused by the action of sulphurous vapors arising from burning coals; 

 which lodging with the soot against the sides of the building, and 

 especially in sheltered positions under the projecting eaves and mould- 

 ing, and thus remaining saturated with moisture under the most fav- 

 orable conditions for acting upon the stone. To this cause, in London, 

 we may attribute some portions of the effects observed in this and other 

 examples. Now it should be recollected that in this densely populated 

 city, with its proverbial " London fogs," and the burning of bitumin- 

 ous coal, the rising of the soot and its condensation on the side of 

 buildings during the heavy damp weather and fogs, would, as a matter 

 of course, produce some effect upon the stone. 



Such conditions, however, can scarcely exist in any Atlantic city 

 * (even if in any American city), with our drier atmosphere and the sul- 

 phurous gases mainly from anthracite coal, which gives no soot. In 

 the Ohio and Mississippi valleys, where bituminous coal is burned and 

 the soot lodges against the buildings, we might possibly look for some 

 effect; but the comparative dryness of the atmosphere would probably 

 counteract the otherwise evil effects from this cause. In considering this 

 cause of deterioration, we shall find it only applicable to special locali- 



