The dimensions of one of the blocks of limestone extracted
from the quarries worked for the formation of the breakwater at
Plymouth were 26 1/2 ft long, 13 ft wide, and 16 ft deep. This
mass, containing above 4,800 cubic feet, and weighing about 400
tons, was blasted three times. Two charges of 50 lbs each were
successively exploded in a hole 13 feet deep, the bore being 3
inches at top and 2 1/2 inches at bottom: 100 lbs of powder were
afterwards exploded in the rent formed by those operations. Each
pound of gunpowder separated from the rock two tons of matter, or
nearly 4,500 times its own weight. The expense of the powder was
L 6, or nearly 7 1/2d. per lb: the boring occupied two men during
a day and a half, and cost about 9s.; and the value of the
produce was, at that time, about L 45.
7. The simple contrivance of tin tubes for speaking through,
communicating between different apartments, by which the
directions of the superintendent are instantly conveyed to the
remotest parts of an establishment, produces a considerable
economy of time. It is employed in the shops and manufactories in
London, and might with advantage be used in domestic
establishments, particularly in large houses, in conveying orders
from the nursery to the kitchen, or from the house to the stable.
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