Blacket was requested to prepare a plan and estimate for a merchants' gunpowder magazine on Goat Island. Blacket's design abandoned the conventional fireproof barrel vault with its massive walls in favour of a thin-skinned structure with a light roof substantially supported by, and tied to, the interior racking system with conventional windows and shutters at the gable ends. The design was criticised but the administration overruled the objections on the grounds that the design was economic and the construction period would be shorter than using a conventional design. In 1854 a new Colonial Magazine was constructed to the north of the existing magazine, which became known as the Queen's Magazine. This was a building of much lighter construction, and was intended for the storage of civilian explosives belonging to the colonial government and local merchants. In 1864 the police station was converted into a laboratory for the preparation of cartridges, requiring the building of a bridge over the cut. The water police were moved to Kirribilli. In the 1870s magazines were built on the east side of the island to house the new explosive dynamite. By this time most of the storage of propellant powders and cartridge manufacturing had moved to nearby Spectacle Island. The increase in mining and public works in the second half of the 1850s resulted in an increased demand for gunpowder, which again resulted in the inability of the magazines to cope with storage requirements. This necessitated in the hire of the brig Lady Mary as a temporary floating gunpowder magazine in 1856. In June 1859 it was decided to construct another magazine on Goat Island using Colonial Architect Alexander Dawson's 1856 plan. The design was similar to the Colonial magazine, but introduced an iron roof which again raised concern amongst military men. The magazine was completed in December 1859. In 1861 the Colonial Secretary raised concerns that the quantity of gunpowder stored on Goat Island was sufficient to "send half of Sydney to the other world." A spectacular explosion in a small store of nitro-glycerine in Bridge Street in 1866 further added to this concern. The Water Police were removed from Goat Island in 1865 and the laboratory for cartridge preparation relocated to the Water Police area in 1866. The use of new blasting preparations such as gun-cotton, nitro-glycerine and lithofracteur at this time further exacerbated these concerns as gun-cotton and nitro-glycerine were more susceptible