In April, 1809, an explosion vessel, devised by Captain Lord Cochrane, of the British Navy, was moved by him against the French fleet then lying in the Basque Roads, under the protection of the batteries of Isle d'Aix. This fleet was still further protected from the approach of this vessel, and other "fire ships" by a heavy boom stretched across the roads in front of the fleet. The boom was contructed of heavy logs and spars chained together, and otherwise secured by anchors and cables. The arrangement of the powder vessel was as follows: The floor was rendered as firm as possible by means of logs placed in close contact into every crevice of which other substances were firmly wedged so as to offer the greatest amount of resistance to the explosion. On this foundation was placed a large number of spirit and water casks, into which 1,500 barrels of powder were emptied. These casks were set on end, and the whole bound round with hempen cables so as to resemble a gigantic mortar, thus causing the explosion to take an upward course. In addition to the powder casks were placed several hundred shells, and over these again nearly 3,000 hand grenades, the whole by means of wedges and sand being compacted as nearly as possible into a solid mass. This vessel was exploded while in direct contact with the boom, which was broken in pieces, not, however, by the direct action of the powder, but by a huge wave caused by the explosion in the water. When the "explosion vessel" blew up the French frigate Indienne was lying within a half cable's length of it, and was not injured in the least.
The following condensed accounts of other explosions you have been kind enough to allow me to extract from the paper recently addressed by you to the War Department upon the explosion of masses of powder:
In June, 1863, a powder magazine in Fort Lyon, defenses of Washington, exploded. It contained about 28,000 pounds of powder. The destructive action was confined principally to the portion of the work immediately above the mine. The parapets of the work, although but some eighty feet distant, were uninjured. The men in the bomb-proofs, not more than seventy-five feet from the explosion, were unharmed. A house 350 yards from the explosion, although considerably shaken, was not destroyed.
An explosion of about 20,000 pounds of powder in a canal-boat moored along side of the pile wharf at City Point, James River, occurred not long since. Some 300 feet of the wharf and the light wooden buildings upon it were destroyed, but the destructive effects of this explosion upon buildings, tents, & c., did not extend beyond 165 yards.
In July, 1848, a schooner tied to the levee opposite the city of New Orleans, La., and loaded with 656 boxes of ammunition and other boxes of ordnance stores, exploded. No injury was done at any considerable distance from the vessel.
At Du Pont's mills for the manufacture of gunpowder and at the various other mills in the country there are repeated and frequent explosions of powder. The injury inflicted does not extend to any great distance.
During the Crimean war, in 1855, a magazine in the Mamelon fort containing about 15,400 pounds of powder exploded. Beyond tearing up the terre-plein just over the magazine no other portion of the work was injured.
In 1769 a square tower of masonry containing 160,000 pounds (French) of powder exploded, but houses were not demolished beyond a radius of 300 toises.