198 Thickness, Cement and Materials of Walls. 



(both scale and shell) caught in the cove at JFiccacoa, 

 in dry seasons, and on the opposite shores : and some- 

 times iiiuch higher up the river. Whether or not, ma- 

 7'ine salt was mixed in the mortar of this building; it is 

 always prejudicial to cement. The muriatic acid (one 

 third of the composition of marine salt) forms, with cal- 

 careous matter, miiriat of lime, which, being deliques- 

 cent, will not indurate. Its strong affinity for water, 

 attracts and retains the humid vapour of the atmos- 

 phere : as I have mentioned, on some former occasion. 

 In thick walls, the masons, if not watched, fill in rubble ; 

 and the offals of the stone, in the interior. Some of the 

 latter are necessar}- in all Avails; but an over quantity is 

 highly injurious. 



In 1779 or 80, there were, in the Philadelphia prison^ 

 1000 British prisoners of war, at one time ; and, in other 

 years, great numbers. Escapes were perpetual ; though 

 the commissary of prisoners and the keeper were, with- 

 out rigour, always on the alert. By the permission of 

 the War Department, in which I then was, the keeper 

 f Elijah Weed, a firm but humane character) walked out 

 daily, with squads of the prisoners, to afford them air 

 and exercise. Few or no escapes occun-ed in these 

 excursions ; they having been restrained by a point of 

 honour; and additionally, because it had been announc- 

 ed that if escapes took place, the indulgence would be 

 discontinued. When locked up, they were under no 

 such honourable, or cautionary obligation. Having 

 been frequently called to an attention to this subject, by 

 the reports of the commissary ; I had an examination 

 made of the souterrain of the whole fabrick ; and was 

 surprized by the result. I found that the cells in the 



