This accident may no doubt be effectually guarded against by strengthening the breech end of the gun as well as the breech itself; but without that precaution it is to be feared that such accidents would be of frequent occurrence. A considerable error may easily be promulgated, as to the heat necessary to be applied ere gunpowder will explode. A late writer says, it is necessary to raise it to 600 degrees before it is explosive. This is a splitting of hairs, and such a palpable mystification, that it is scarcely worth noticing. But I will explain: if you place upon a plate a few grains of powder, by heating the plate underneath (for instance, on a smith’s fire,) you will see the sulphur giving out a blue flame, it being easily fused. As the plate becomes heated to nearly a red heat, the whole explodes, in consequence of the charcoal and nitre not being hot enough to allow the gases generating the heat to be liberated; but as soon as this does take place the explosion ensues. Now, it is a well known fact, that the smallest particle of matter possessing above 600° of heat, will ignite any quantity of powder it comes in immediate contact with; we will suppose with one portion of charcoal, one of sulphur, and one of nitre (it matters not how small they are: a ten hundredth part of the substance of one of the smallest grains of powder would suffice), and if it has the means of communicating to these small portions 600°, this is sufficient, as their explosion induces also that of the very largest quantity: for it ought to be perfectly understood, that a great explosion is but so many millions of small ones combined, and by their united force effecting the great results we see. The ingredients of powder are ground and intimately mixed together on the bed of the mill to the great extent they are, to the end that, if possible, there shall not be in the composition two grains or portions of one ingredient in immediate contact with each other; but that, when the ignition does take place, each may be present to add its peculiar gas, in order that each affinity may be supplied. Thus becomes evident the necessity of a most extensive incorporation, a blending and equal division of mixture throughout the whole material. The advantage of unglazed gunpowder is here fully shown; for it presents an inequality, a roughness of surface, over which the flame from the percussion mixture cannot travel without igniting some of the prominent parts, and thus the whole. You may glaze powder and make it so smooth that it would be very difficult indeed to ignite; but except that it enables the powder to resist moisture better, it is otherwise very detrimental, as tending both to prevent ignition and lengthening the period of effecting it.