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about 244 times as much space as when it lies quiescent in the gunpowder. The space to which this is again expanded by the heat of the flame, is about four times as much: so that the force or pressure of fired gunpowder, is about 1000 times greater than the pressure of the atmosphere, which being equal to fourteen pounds every square inch, the force of gunpowder upon

the same, must be equal to 14000 pounds, which will account for the astonishing effects of cannon balls. *

Many chymists, however, have ascribed the cause of fulmination to a saline, and to a sulphurous, as well as to an aerial principle; and there are not a few, who have supposed it to depend upon several of these united. But, what we have said above, is, I believe the true solution. Yet, forcible as gunpowder may appear to us, there is yet another substance, an arrum fulminans, which is still more powerful. Various experiments have been made on the comparative force of these powders. The aurum fulminans, notwithstanding celebrated philosophers, such as Boerhaave, Macquer, Spielman and others, contend it is not accounted for,-is simply the calx of gold; for by whatever method gold be dissolved, and precipitated (provided the volatile alkali be present either in the menstruum or the precipitant) a yellow precipitate is obtained, which, when well washed in water, and cautiously dried, is the aurum fulminans. The weight of this calx, when well washed and dried, exceeds that of the gold employed, about one fifth. A single cubic inch of gunpowder, generates about 244 inches of elastic fluid, but the same quantity of aurum fulminans, yields at least four times as much; and hence, from its copious and instantaneous eruption, and violently striking the common air, its wonderful explosive force.* The trial of this, indeed, was made by our Royal Society. Equal parts of gunpowder and aurum fulminans, were distinctly included in iron globes, and placed among burning coals. Those which contained the aurum fulminans were burst with violence, while the other re“mained perfectly at rest and silent. But fulminant silver, as I have before remarked to you, is still more violent than the aurum fulminans.

dissolved, * Philosophy of the Elements.

The knowledge of these circumstances, conducted philosophers to more applicable experiments, as to similar phænomena in nature. Accordingly it was discovered,* that mixing, for instance, twenty-five pounds of powdered sulphur with an equal weight of iron filings, kneading the mixture together by means of a little water, into the consistency of paste, and putting it into an iron pot covered with a cloth, and burying it a foot under ground, that in eight or nine hours afterwards, the consequence would be a true volcano. Hence it is natural to conclude, that the body of the earth must have various spiracula or out-lets, which, like ulcers in the human frame, discharge peccant humours; and which, frightful as they may seem to our terrified imaginations, yet serve to prevent more dreadful and destructive effects in the constitution of the globe. Ætna, Vesuvius, and other burning mountains, in this manner, it is probable, throw off their intestinal superfluities.

cordingly * Bergman.

The causes of the concussions of the earth, were reduced by the ancients to three: water, fire, and air. Thales, who held the mosaic doctrine, that the earth is founded upon the waters, supposed that nothing more was necessary to produce earthquakes, than some irregular agitation of the waters that are under the earth. Others, seeing that nothing can resist the force of boiling water when turned into vapour by fire, held the idea which Seneca expresses, “cum pluribus locis ferveant (ignes) necesse est in

seeing * M. Lemery

gentem vaporem sine exitu volvant. Videmus “aquam spumare igne subjecto : quod multo “magis illum facere credamus, cum violentus “ac vastus ingentes aquas excitat: tunc ille va"poratione inundantium aquarum, quicquid “pulsaverit agitat.” He adds, also, that the best and greatest authors all agree, to derive earthquakes from the motion of subterraneous air. Aristotle, and Theophrastus, were of opinion, that there is a constant evaporation from the earth upwards, which, if it has not vent, returns upon itself, and is condensed, till it forces its way, and in so doing, shakes the superior parts of the earth. Even Seneca himself has one very subtle argument to prove, that air is the true cause of earthquakes: because in all cases when air makes an effort to break out, its first shock is always greatest, the air being then densest; and all the succeeding ones lessen by degrees, as the air becomes rarefied. Fire, however, does not follow this rule: its first effort is not greatest, but it rises to its ultimatum by degrees. Pliny, some years before him, was of the same opinion.

These

These opinions, on certainly the greatest and most terrible phænomena of nature, were those which alone were adopted by the generality of philosophers. But though concussions might have been extended, even though, for instance, a violent eruption of Mount Ætna might have caused an earthquake over the whole island of Sicily, it yet could not, with much probability, have been supposed to have reached three or four hundred leagues distant. In order to account for this, however, it was said, that all inflammable matters capable of explosion, generate a large quantity of air; that this air, produced by the fire, is in a state of very great rarefaction, but by means of compression in the bowels of the earth, is driven to the production of these violent effects. Let us suppose, therefore, said they, that at a very considerable depth, a hundred or two hundred fathoms, there be found pyritæ and other sulphurous substances, and that by the fermentation produced by the filtrating of waters, or other causes, these happen to take fire; let us see what will be the result : in the first place, these substances are not disposed in horizontal strata; on the contrary, they are contained in the perpendicular fissures; in the caverns at the foot of those fissures, and in other places where

the

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