Thickness, Cement and Materials of Walls. 201 



cannot enter the stone, it is called, vulgarly and impro- 

 perly, sweating ; though it is occasioned by the texture 

 being impervious, and not permitting the damp to en- 

 ter. Faults and cellars, to be dry, should be built with 

 soft, and clean gritted stone. Hard stone ai'e thought 

 best, to withstand attempts at breaches in jails; and for 

 forts, and other works requiring strength; or subject to 

 forcible assaults. However true this may be to a cer- 

 tain point, the idea is generally extended too far. A 

 soft, tough, curly stone, will not break neai'ly as easy 

 under the sledge; or separate by 'means of the wedge, 

 or gad. It will stand battering by cannon balls, far 

 better than hard or flinty stone. It is the same with 

 timber. Hard wood will soon be shattered, broken, 

 riven and destroyed, by a battery of cannon : whereas 

 the palmetto, and other such woods, being spongy and 

 soft, defy the attacks of the heaviest balls. Fort Moul- 

 trie, in South Carolina, was during our revolutionaiy 

 war, an incontrovertible proof. Hard stone resists, and 

 is shocked and broken throughout. But the balls 

 make holes in their passage through soft stone, or wood, 

 very little larger than their diameters; if they do not 

 bury themselves therein, which sometimes happens. 

 This fact can be ascertained; and I have seen sundry 

 proofs of it. Some spongy w^ood will nearly again 

 close the perforation. 



If Anderson'' s ideas be correct, the solidifying of mor- 

 tar depends on the coating and crystallization of the 

 lime, on the surface, and in the cavities, of everj^ grain 

 of sand: which he says, is the better, the more it is sili- 

 cious and rough ; and furnished with corners and protu- 

 berances, encreasing the surface. He prefers river 



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