56 TRANSACTIONS OF THE [N^OV. 23, 



Mr. R. M. Caffall read a inipcr on 



THE PRESERVATION OF BUILDING-MATERIALS BY THE APPLI- 

 CATION OF PARAFFINE, AS RECENTLY USED UPON THE 

 OBELISK. 



(Illustrated with apparatus and experiments.) 



In discussing the subject of waterproofing and preserving 

 building-materials, it will be necessary first to consider the 

 causes of decay in such materials, and how it may be prevented. 



The most powerful natural agent that disintegrates stone and 

 other similar building-material is undoubtedly water, especially 

 when it freezes after it has entei'ed into the interstices of the 

 stone, as it then exerts a force that is irresistible. 



Mr, Dexter A. Hawkins has told me that he had seen in the 

 New England States immense boulders of granite near the road- 

 side which had been so powerfully acted u})on by freezing water, 

 that it was the custom of those living there, when they required 

 material for repairing roads, to back their wagons up to one of 

 these apparently indestructible masses of rock, and by simply 

 striking it with a pick, it would crumble into small i)ieces, which 

 were then shovelled into the wagon, drawn away, and spread 

 where required. He also mentioned having seen in the cafions 

 of Colorado, and elsewhere in the West, immense banks of debris, 

 one hundred feet or over in height, formed of matter forced off 

 by frost from the face of the rock cliffs above. 



The evidence that water is the most destructive agent can be 

 seen on any building where the exposed stone remains the long- 

 est in a wet state, as, for instance, the base of the wall near the 

 ground, the stoops, the stonework under balconies, porticos, 

 window sills, etc. 



But there are also other causes of decay, the chief one, in my 

 opinion, based on long and careful observation, being the white 

 salts which are so often seen upon our best buildings, those of 

 brick more particularly. ■ They are especially ruinous to building 

 materials, arc most difficult to overcome, and hence deserve 

 extended notice. 



(1) As to their Origin. — Tiicse salts exist naturally in the clay 

 from which the bricks, terracotta, etc., are made; also in the lime 

 used for mortar or cement. It is a well-known fact that many of 

 the salts that are present in clay are insoluble while the clay is in 

 its raw or natural state, but that the action of fire renders them 

 soluble. The same result also follows the admixture of lime with 

 the clay. Hence, agriculturalists apply lime to tlic clay soils to 

 render them more fertile, because the salts are made soluble by 

 the action of the lime, and the plants are then able to assimilate 

 them. 



