Purfleet Play Centre and Attached Wall to S

Purfleet Play Centre and Attached Wall to South

Proof house built in the mid-1760s to designs by James Gabriel Montresor, Royal Engineer, and constructed to a similar design as the main magazines at Purfleet. The building is constructed of Flemish bond brown brick with Portland stone dressings and a gabled slate roof.

The main structure is a tall single-storey building on a square plan. The south elevation, which faces the Thames and the surviving magazine from the original group of five, features an open pediment framing a semi-circular lunette to the gable end. The east and west return elevations each contain 3 bays with a tall central semi-circular arched window flanked by blind windows above sashes, all set under cambered arches of gauged brick. The north elevation, abutting a steep scarp, has a doorway inserted into a tapered and slightly projecting central bay which rises into a similar open-pedimented gable.

The interior has a suspended ceiling, but corbels remain from the former gallery, which was originally provided for the testing of gunpowder. Proof houses were used for testing small quantities of gunpowder by igniting it with a hot iron on a glass, porcelain or copper plate. This scientific testing function took place within the context of eighteenth-century scientific development and Britain's efforts to standardise and improve powder quality for the army and navy during the critical period of Britain's growth as a naval power following the Seven Years War.

Single-storey outbuildings are attached to the south, constructed of similar materials and probably built as a shifting house for changing into specialist magazine clothing. These consist of a small hip-roofed central block attached at right angles to a narrow range extending westward, with a similar pedimented end gable to the west. A tall brick wall, extending approximately 10 metres, stands immediately to the south of this range, facing onto Centurion Way.

In the 19th century the building was used as a Copper Hoop Store. It survives from the powder depot at Purfleet alongside the associated magazines built by Montresor, including No. 5 Powder Magazine and the Clock Tower. The only other surviving proof house is the early 19th-century example at the Marsh Works in Faversham, Kent. The plan and form of this building, with its gallery, relate clearly to its function as an 18th-century laboratory building. It represents a very rare, possibly unique example of such a structure, with the gallery design later repeated in Sir Frederick Abel's laboratory of the 1860s at Woolwich's Royal Arsenal.