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On the Thickness^ Cement^ and Materials of JFalls of 

 Farniy and other Buildings, By Richard Peters. 



Read March 8th, 1808. 



Sometime ago, I took down a thick wall ; and observ- 

 ed the interior rotten and friable, (crumbly) although 

 it had been built 60 years. Had the mortar been pro- 

 perly composed; time would have rendered it perfectly 

 solid. But I found that it had been overcharged with 

 lime ; and that sandy loam had been used, instead of 

 pure sand. The masons of this day know better ; but 

 they waste lime, by mixing an undue proportion with 

 their mortar, because it works more freely under the 

 trowel; and thus, for their own ease, add to the expence 

 of their employer. I consider walls to be thick; when 

 they exceed 18 inches. 



Thick walls^ are not, in general, the strongest. A 

 mistake of this kind was made, w^hen the Philadelphia 

 prison was erected. The interior cement was not indu- 

 rated, for many years after the erection ; owing to the 

 thickness of the walls, in part ; and also to a defect in 

 the quality of the materials, and the composition of the 

 cement. Whether the sand was obtained where the 

 water of the Delaware, at certain seasons of long 

 drought, is brackish, I know not. Marine salt is depo- 

 sited, in such seasons, higher up the tide waters of large 

 rivers, than is generally imagined. This may be ascer- 

 tained by filtration and decomposition ; and by the ap- 

 pearance of sea fish, at such periods, in places higher 

 than those of their usual resort. I have known sea fish 



