SCHUYLKILL PERMANENT BRIDGE. 5^ 



will be appreciated, when the object of it is rendered in its 

 duration^ as well as other attributes, r&2\\y pefmanent. It 

 would be a reflection upon their understandings, and, with 

 the knowledge we have on the subject, a breach oi our trust, 

 to practice a dangerous and false oeconomy, and thereby in- 

 cur the penalty of certain destruction. I beg the excuse of 

 the board for giving my sentiments at length on the subject. 

 It is one on which I thought it my duty, whatever may be 

 the result, to be explicit."* 



RICHARD PETERS. 



* The following notes, omitted to be inserted in page 40, 

 are here added. 



" Grouted,'''' Grout is mortar of the same proportions, in its 

 component parts, with that used in the common way. But 

 this is in ?i JIuid state ; and, from time to time, poured on the 

 courses of masonry, as the work is in progress. It searches 

 out, and fills, every vacancy ; and completely embodies the 

 mass. All masonry, faithfully built, should be thus treated. 

 Contract xvork is too often slighted, to save the materials of 

 common cement ; brick walls as well as those of stone should 

 be grouted. In large works it is peculiarly necessary. 



" Tarras''' is a species of lirne^ procured from Holland 

 (called Dutch tarras) and several parts of the European Con- 

 tinent. It has the quality of becoming insoluble (or harden- 

 ing) under xvater; like common limey in atmospheric air. It 

 is a substitute for Puzzolan earth, found in Italy ^ in the vici- 

 nity of Volcanoes ] it being volcanic matter. 



Welch LimCy in a considerable proportion was used ; a sufTi- ' 

 cient quantity of tarras not having been procured, and no 

 difference, in their qualities or effects, was perceived. This 

 lime is found on part of the coast of Wales ; and is said to be 

 thrown up by the sea^ on its shores. It is believed to have 

 calcareous matter (which abounds in the ocean, as well as in 

 the earth) for its basis, combined with Jixed air or carkonh: 



