Although theory is not capable of estimating the force, or what is the same thing, the quantity of powder necessary to produce a certain effect, long experience has established the relative quantities of powder which are necessary under different circumstances, with sufficient accuracy for all practical purposes.
These different circumstances are always of the same kind with reference to the artillery, where the range is the only thing that varies; whilst in blasting they are very various, loose earth has frequently to be blown up and at other times, solid rock; sometimes, the object is to destroy and hurl the fragments to a distance, and at others to get rid of them in a manner as little dangerous as possible, as for instance, in cases of civil engineering.
When all was arranged, care was taken to stop up the entrances to the chambers with dry sand.
Besides the charge of powder, a considerable quantity of air was enclosed in the chambers.
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The circumstances attending the explosion, the absence of smoke and report, prove that the charge was just sufficient to overcome the resistance.It would have been quite contrary to the desired result to have actually blasted the rock into the air, or hurled the fragments about with a great loss of powder; the only object was to separate the mass of rock, and allow it to roll into the sea.The accuracy with which the necessary quantity of powder had been estimated, was proved by the wonderful success of the experiment.To reach from thence Shakespeare's Cliff (near Dover) in a direct line, the projecting rock at Round Down, an immense mass of chalk, which exactly intercepted the line, had to be removed. over the top of the rock to the chambers below, and always resting on the ground, terminated in very fine platina points in the middle of the mass of powder.
The project for removing this rock, which occupied the space of 2400 cubic fathoms, and weighed one million tons, by one single blast, was successfully carried out by Mr. For this purpose, a channel, 361 fathoms long, was made in the direction of the railroad, and perpendicular to this, three shorter side channels: At the end of each side channel, a perpendicular shaft was sunk to the powder chambers, each of which was 13.4 ft. By making connection with the battery, these points were brought to a red heat, and the enormous charge of powder ignited in the same moment.
For the latter purposes, the use of powder has very much increased since the introduction of railroads has given.