Art. XIX. On a Method of Augmenting the Force of Gunpowder.
Art. XIX. On a Method of Augmenting the Force of Gunpowder.
Extract of a Letter to the Editor, from Colonel George Gibbs.
I employed, the last year, a man in blowing rocks, and having seen an account of a method of substituting a portion of quick lime for a part of the gunpowder usually employed, I was induced to make a number of experiments upon it. I now send you the results in the certificate of the person employed, whose statement might be relied on, even if I had not superintended myself a number of the experiments.
"Sunswick Farms, Oct. 19, 1817.—I certify that, having been employed by Colonel Gibbs in blasting rocks on his farm, I, by his orders, made use of a composition of one part quick lime and two parts gunpowder, and uniformly found the same charge to answer equally well with a like quantity of gunpowder. I made upwards of fifty blasts in this manner, as well as several hundreds in the usual way, and can therefore depend upon the accuracy of this statement. I found, however, that when the powdered lime was mixed with the gunpowder the day before, that the effect was diminished. It should be always used the day it is mixed.
(Signed) T. Pomeroy."
This preparation was made generally in the morning, put in a bottle and well corked, to prevent the access of the external air. The rationale of the process was not explained in the original recommendation, but it soon occurred to me, that it must be owing to the desiccation of the gunpowder by the lime.
The attraction of moisture by gunpowder, is known to be very great: according to Rees's Cyclopedia, upwards of 16 per cent. has been absorbed, and that the removal, simply, from near the fire to the corner of the room, produces a considerable change in its weight. I presume, therefore, that the lime, which in its caustic state has also a great affinity to water, attracts a portion of it from the powder, and leaves it in a state of dryness best fitted for inflammation. But if the lime should remain too long mixed with the powder, it would probably attack the water of crystallization of the saltpetre, and, according to Count Rumford's idea, destroy a great part of the power. If also left exposed, attractions of moisture would take place from the atmosphere, the gunpowder would remain surcharged with humidity as before, and the lime would be only an inert mass.
The examination of this subject led me to consider the increase of the power of gunpowder in various situations, and of its use in the field. It is well known that after a few discharges a cannon becomes heated, and the range is much greater, as well as the recoil. The charge of powder is therefore reduced about one quarter, to produce the original effect. As I have not heard or seen any explanation of this fact I shall take this opportunity of mentioning, that it appears to arise from the same cause as the first explained, viz. the desiccation of the powder. No person will dispute the heat acquired by a cannon, or even a musket, after repeated discharges; and this heat must volatilize or destroy a great portion of the moisture combined with the powder, assist its speedy inflammation, and perhaps add to its power, by causing a more perfect combustion of the inflammable parts of the gunpowder. This would cause a much greater volume of gas to be produced, and the high temperature would also greatly augment its elasticity; and it is well known that the effects of gunpowder depend upon the rapid production and high degree of elasticity of a great quantity of aeriform fluids or gases.