Powder Magazine

Powder Magazine (HM850)

Location: Philadelphia, PA 19153 Philadelphia County
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Country: United States of America
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N 39° 52.531', W 75° 12.809'

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Report from the Fort
17 August 1867 · Lieutenant Colonel C. S. Stewart

New Magazine - is now essentially completed and ready for use. During the year one third of the inner and main arches have been turned; the south wall built; the ventilator flues carried up to the proper height; temporary covers attached thereto; floor timbers and flooring put down and doors hung - 113 cubic yards of concrete backing put in position; roof surface covered with 210 square yards of asphaltic mastic: 900 yards of rammed earthen bankment completed and 822 square yards of sodding placed thereon .
National Archives Philadelphia

The construction of this magazine was proposed in 1864 to hold 1000 barrels of powder (100 rounds for each gun) and to replace a deteriorating structure from 1809. A depression in the ground near the Officers' Quarters has remained since 1872 when the old magazine was torn down. The new magazine was designed with two concentric brick and concrete barrel vaults separated by an air space to ensure security and insulation from moisture. The air space between the two walls is visible at the jambs of the interior doorway. Note also the indirect tunnel and number of doors necessary to reach the chamber. Niches in the wall would have been used for lanterns. The sodding that covers the structure on the outside was designed to provide protection from outward explosions or external bombardments.

All the powder magazines at the fort were intended to store powder in casks or barrels for both priming and firing cannon. Cannon were tested or proved periodically even in times of peace. A report from 1869 describes testing the five 15" Rodman guns, two in the water battery (demilune) and three from the ramparts of the fort. For gun number 37 in the water battery, the report states that it was tested "On the 4th of July 1865 - blowing away part of the breast height wall from too great a traverse given the gun."
HM NumberHM850
Placed ByFort Mifflin Historic Site
Marker ConditionNo reports yet
Date Added Friday, September 26th, 2014 at 3:47am PDT -07:00
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Locationbig map
UTM (WGS84 Datum)18S E 481744 N 4413962
Decimal Degrees39.87551667, -75.21348333
Degrees and Decimal MinutesN 39° 52.531', W 75° 12.809'
Degrees, Minutes and Seconds39° 52' 31.86" N, 75° 12' 48.54" W
Driving DirectionsGoogle Maps
Area Code(s)215
Closest Postal AddressAt or near 8300-8390 Fort Mifflin Rd, Philadelphia PA 19153, US
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