88888 ip. in. lbs. feet. 7 88 7 1375 3 1670 in. 10 of an inch 10 of an inch of an inch 6 of an inch 11 Broke a beam over head; and on taking up the floor for the purpose of putting up new props, it was found that three of the floor joists were ruined by the severity of the previous shocks. An iron axletree, 14 inches in diameter, of one of the pillars, f, over head, was broken off. Broke the axle of one of the pulleys over head. The beams supporting these pulleys were brought nearer together, and iron trunnion plates were placed under each axle to prevent its being forced into the wood. Broke the rope k, k, connecting the chain with the sliding board, e, under the piston. A chain was substituted in the place of this rope, and the apparatus thus made to conform in all respects, with the description which has been given of it. In this and all other cases where the piston was forc forced thro'ed through the tube, a quantity of fine dust, apparthe tube. rently arising from the pulverization of a part of the sand, collected on the sides of the tube and at the top of the piston. 94 of an inch 1-16 9 of an inch none Piston forced thro 32 inches. 10 Pn. forced through 104 7 361 3 8 105 8 361 3 106 9 615 3 107 10 615 Broke a large iron hook at the tube end of the large chain. Broke the large chain in four places. Broke one of the hooks connecting the chain, k, k, with the sliding piece, e. Broke the large chain. The apparatus could not, without considerable trouble and expense, be made to sustain the force necessary to expel 8 inches of packed sand, and the further pursuit of this inquiry was therefore abandoned. The interior diameter of the tube was now increased to 1 7-16 in inches, with which all the remaining experiments were made. Broke the chain. 113 11 1630 3 3 of an inch Broke the chain. 3 of an inch of an inch 6 Pn. forced through 913 inches. Broke the chain. This chain being much strained & worn by previous shocks a new one was procured. Broke the chain. Observations on Table III. The tube was of brass, cast about one-fourth of an inch thick, the interior diameter being one and one-fourth inches as far as experiment No. 111, after which it was increased to one and sevensixteenth inches. A chain, capable of supporting nine tons, was substituted for the rope, h, h, h., and after experiment No. 90, a strong chain was employed in lieu of the rope, k, k. The apparatus was strengthened in a variety of ways to enable it to resist the great shocks it was subjected to. It appears from this table, that to expel seven inches of dry packed sand from a tube one and one-fourth inches in diameter, it was necessary to employ a weight of 2286 pounds falling through a space of three feet eleven inches. A weight of 2644 pounds falling three feet, was insufficient to force from the same tube eight inches of sand. Sand poured loosely into the tube, without being packed, offered much less resistance. Seven inches of loose sand was expelled by a weight of 361 pounds falling three feet eight inches; nine inches by a weight of 615 pounds, falling three feet nine inches; and ten inches by a weight of 870 pounds falling three feet ten inches. Eleven inches in a tube of one and seven-sixteenth inches bore, was expelled by 1630 pounds, falling three feet ten inches; twelve inches, by 2136 pounds, falling three feet six inches; and 2136 pounds, falling three feet nine inches, did not drive out thirteen inches of loose sand. The strength of the apparatus did not admit of carrying these trials further in this way, and it was resolved to use gun-powder; but in the meantime to determine the resistance which would be offered by the sand to the entrance of iron rods of much less diameter than the bore of the tube, the following experiments were made. Rods of one-fourth, one-half, and three-fourths of an inch diameter were used. The tube being one and seven-sixteenths inches in diameter, a wooden piston having a hole in its centre, just large enough to admit the rod a, in the manner indicated by the annexed sketch, was placed in it, and the rod being entered into the piston, the sand was placed above it as usual. With this apparatus, the experiments contained in table IV. were, among others, tried. Observations on Table IV. The resistance opposed by the sand to the entrance of a rod of smaller diameter than the tube, was very great, and increased with the size of the rod. A weight of 2033 pounds was required to force a inch rod through 8 inches of sand. With 12 inches of sand, a weight of 3150 pounds was required to force the same rod, sharpened, 2 inches into the tube. Sharpening the inch rod, seemed rather to increase than to diminish the resistance. A half inch rod was forced through 8 inches of sand, by 870 pounds falling 4 feet. With 13 inches of sand, a inch rod was forced only 1 inches, by a weight of 1880 pounds falling S feet 6 inches. A rod of an inch in diameter, was forced through 8 inches of sand by 1120 pounds, falling 3 feet 10 inches; and the same rod was forced through 13 inches of sand by 2136 pounds, falling 3 feet 3 inches. In all cases the sand immediately before and around the rods, was crushed to a fine powder. Trials with Gun Powder. 166. A musket barrel, of three-fourths of an inch bore, was charged with wo inches of powder and thirteen inches of packed sand, there being neither wad nor plug between the sand and the powder. On firing, the barrel was burst, but the sand was not driven out. 167 & 168. A brass blunderbuss barrel of three-fourths of an inch bore, was charged with one inch of powder and ten inches of packed sand, a wooden plug being placed between the powder and sand. On firing, the plug was split, and all the sand driven out, but the pieces of the plug remained in the barrel, which was apparently uninjured. The same barrel burst with one inch of powder and ten inches of packed sand, with a conical wooden plug between the sand and the powder. 169. A pistol barrel of nine-sixteenths of an inch bore, burst with one inch of powder and eight inches of packed sand, without wad or plug. 170. An old musket barrel of three-fourths of an inch bore, was loaded with three-fourths of an inch of powder and five inches of packed sand, without wad or plug. On firing, the barrel was burst, but the sand was not driven out. 172. A piece of musket barrel, taken from near the muzzle, and open at both ends, was charged at one end, with five and a half inches of brick dust, hard rammed, and at the other, with five and a half inches of sand, well packed, with one inch of powder between them, a priming hole being bored to communicate the fire. The explosion of the powder burst the barrel, but neither the sand nor the brick dust was driven out. 177 to 184. A pistol barrel made of twisted iron, and of great strength, the bore being eleven-sixteenths of an inch, was fired with three-fourths of an inch of powder, and the following loads of sand, each one, with, and without, a wad, viz: three inches, four inches, five inches, and six inches. In all these trials the sand was driven out without causing the barrel to burst. 185. The same pistol barrel was loaded with one inch of powder, and eight and one-fourth inches of sand, with a conical plug between the sand and the powder. On firing, the sand was forced out. 186. The same barrel was charged with one inch of powder and eight and one-fourth inches of sand, without wad or plug. On firing, the sand was driven out, and the barrel was burst. In order, if possible, to determine a limit to the resistance opposed by sand, it was resolved to make use of a twenty-four pound cannon. It was thought not improbable, that by the use of clean dry sand, which is generally obtained in the vicinity of the sea coast batteries, a ready method would be discovered of effectually destroying heavy guns, an object which is occasionally of great importance. Application was therefore made to the ordnance department for permission to experiment with an old pattern twentyfour pounder, laying at Fort Adams, which permission was very liberally and readily granted. The length of the bore of this piece was about nine feet, and the diameter of the bore 582 inches. It was first fired in a horizontal position, with eight pounds of powder and one foot of sand, after wards with the same quantity of powder and two feet of sand, again with the same quantity of powder and three feet of sand, and so on, the depth of the sand constantly increasing by one foot, until the bore was full. The gun was then placed in a vertical position, and loaded with the same quantity of powder, and filled up to the muzzle with sand, well packed, without wad or plug. It was afterwards charged in a similar manner, a cone of wood being interposed between the powder and the sand. In these two cases the fire was communicated to the charge by means of a priming tube, passing down through the sand from the muzzle of the gun. Afterwards the gun was charged in the same manner, and fired by means of the vent. A better quality of powder was then used, and the quantity was increased to sixteen pounds. The gun was several times fired with this charge, the bore being filled up to the muzzle with sand well packed. In every in stance the sand was forced out without apparent injury to the gun. It appeared, therefore, that the resistance of the sand, though very great, was not sufficient to burst a twenty-four pound cannon. The most probable explanation of the foregoing phenomena, appears to be, that whenever direct pressure is applied, the angular and irregular shaped fragments composing the sand, immediately form themselves into a natural arch, supported against the sides of the tube. The annexed sketch indicates the manner in which this may take place. In every instance where the sand was violently forced from the tube, the sides of it were found to be lined with a quantity of fine dust, and a mass of pulverized sand was generally found at the head of the piston A. The inside of the tube was abraded or scratched, particularly at that part, a short distance above the piston, against which the arch, or more strictly, the inverted dome of sand, may be supposed to have abutted. The dust found on the sides of the tube was always of a blueish colour, which was attributed to the intermixture of a small portion of metallic oxide derived from the brass. Some experiments which were made went to show that it was very important that the sand should be perfectly dry. The injurious effect of moisture may be explained by supposing that it impedes the free motion of the particles among themselves, and prevents their promptly assuming the arch form; it cements the sand into a mass, which is expelled from the tube as a solid body would be. In the case of the twenty-four pounder, it appears that the force necessary to burst the gun, was greater than that required to reduce sand to an impalpable powder, that is, to crush and destroy the materials of which the arch of sand was composed. It is probable that coarse emery, from its extreme hardness, would oppose a resistance sufficient to burst a cannon, but an opportunity has not offered to make the trial. The experience at Fort Adams, proves that the resistance offered by sand is quite sufficient for blasting rocks, and the advantages attending its use, are, that it is much less troublesome than the usual mode, and that it is perfectly safe. To ensure success, the space left above the powder should have a length of ten or twelve times as great as the diameter of the hole. To communicate fire to the powder, a slip of paper is rolled into a tube about three-sixteenths of an inch in diameter. This priming tube is secured by being tied round in two places with thread, and one end is made a little larger than the other, so that any required length may be obtained by joining several together. The charge of powder being in its place, the priming tube is inserted and filled, it is then pressed against one side of the hole, and the sand is slowly poured in. A slender stick of hard-wood is rapidly worked up and down in the sand as it falls to the bottom, and thus every part becomes well packed. By this mode of operating there is, of course, no danger of communicating fire to the powder in the act of loading, an accident very liable to happen in blasting in the common way. The safest and most convenient method of firing the blast is by means of a small slip of paper which has been dipped in a solution of salt-petre, and dried. It was intended to make examinations on other points connected with the phenomena observed by M. Burnand, but the requisite leisure has not been at command. The subject merits further investigation with a view to making useful practical applications of some of the remarkable properties which sand is found to possess. |