OF THE

FRANKLIN INSTITUTE

OF THE

State of Pennsylvania,

AND

MECHANICS' REGISTER.

DEVOTED TO

Mechanical and Physical Science,

CIVIL ENGINEERING, THE ARTS AND MANUFACTURES, AND THE RECORDING OF

AMERICAN AND OTHER PATENTED INVENTIONS.

AUGUST, 1836.

Practical and Theoretical Mechanics.

Experiments on the resistance of sand to motion through tubes, with especial reference to its use in the blasting of rocks, made at Fort Adams, Newport harbour, under the direction of Col. Totten. By Lieut. T. S. BROWN, of the Corps of Engineers.

(CONTINUED FROM p. 8.)

For the purpose of examining further the degree and nature of the resistance offered by sand when it is attempted to force it through a tube by direct pressure, the following apparatus was arranged, after a few preliminary trials, which had given some idea of the power it would be necessary to apply. A side and end view, and a plan of the apparatus are given in the cut on the next page.

The strong cast composition tube, a, about fifteen inches in length, which contained the sand, was held in a vertical position by being passed through the block, c. The pressure was always applied to the bottom, and the collar, b, cast upon the tube, prevented its being forced upwards. The block C, was secured in its place by being let into the four posts, 1, 2, 3, 4, passing from the floor to the ceiling. These four posts formed a very stable frame work, and between each pair, the space, g, permitted the sliding board, e, to move freely up and down, and secured the proper direction to the pressing force. For the sake of distinctness this space, g, has been represented wider on the sketch, and the sliding board, e, thicker, than they actually were. The pressure was applied by means of a movable piston within the tube, connected by means of the iron rod, d, with the sliding board, e. This sliding board was attached, by means of the chains, k, k, h, h, h, passing over the cast iron pullies, f, f, to the platform, p. Of course any weight placed on this platform communicated a corresponding pressure upwards to the piston within the tube. The chain h, h, was of the best VOL. XVIII. No. 2.-AUGUST, 1836.

7

Peru iron; the wire was about an inch in diameter, and the chain had been proved with 9 tons dead weight. The pulleys, f, f, were about a foot in diameter; and their axles were of wrought iron an inch and a half in diameter. When a dead weight was to be applied, the platform was loaded in the position, p, but if a violent shock was to be produced, the platform was held in the position, p', by means of the cord, r, r, r,funtil it had received the proposed load; the cord, r, r, r, being then suddenly cast loose, permitted the loaded platform to fall freely by its gravity, until it had straightened the chain, when it was either entirely arrested by the resistance of the sand in the tube, or it forced its way to the floor in consequence of the yielding of the sand, or of the fracture of some part of the apparatus.

There were other minor details which it is not necessary to particularize. The fixtures were not brought to the degree of strength just stated until after many trials, and the repeated failure of nearly every part of the apparatus; and, as will be seen, a limit was soon attained, beyond which the experiments, even with this degree of strength, could not be carried. The weights used were bricks. The piston was so arranged as to move without friction when the tube was empty, and at the same time to prevent the es cape of the sand when the tube was charged. Trials were made with sand poured loosely into the tube, and with sand carefully packed. The packing

• Peru, Clinton county, New York. The iron from this locality possesses a remark. able degree of tenacity.

was performed by means of a small sharp stick which was worked up and down in the sand as it was slowly poured in. This method was found to be the best, and is the one always used at Fort Adams, in charging drill holes for sand blasting. The sand used was dry and free from dust, and from all particles which would not pass through a hole th of an inch in di

ameter.

A preliminary series of experiments was tried, the results of which will not be given, as they were all subsequently repeated in a more careful and

accurate manner.

In the second series, a tube of tin, fifteen inches long, having an interior diameter of 1 inches, was used instead of the cast composition tube, a, above described, and a 3 inch bolt-rope instead of the chain, h, h, h. The following table indicates a portion of the results obtained.

Observations on Table I. The tube was of the kind called double tin, 15 inches long, and 14 inches in diameter, folded at the seam, and strongly soldered. The piston was just inserted into the bottom of the tube, and the weights given in the fourth column, were those which were necessary to force it quite through the tube, with the sand before it. In the experiment No. 46, where 9 inches of packed sand were tried, after a weight of 1900 pounds had been placed on the platform, without producing any effect, an effort was made to drive the sand from the tube by forcing up the sliding board, e, with a lever. In this operation the tube was bent, and split at the soldering, but the sand was not forced out. It was soon ascertained that very great weights would have to be used when the depth of the sand was equal to, or greater than four times the diameter of the tube, and that the process would be tedious; it was accordingly resolved to abandon the use of dead weights, and employ the momentum of falling bodies. Previously to making these trials, a glass tube 3ths, of an inch in diameter, was procured and experimented upon. It admitted six inches of sand to be forced out of it, but with 8 inches of sand well packed, it burst when a dead weight of 550 pounds was applied.

Observations on Table 11. The tube and rope were the same as described in observations on table I. The experiment No. 61, the top of the sand was made even with the top of the tube before the experiment was begun, by pushing up the piston until only so much space was left above it, as it was intended the sand should occupy. This rule was observed in all the subsequent experiments. This table shows that it required a weight of 1320 pounds, falling S feet, to force 5 inches of dry sand out of a tube 14 inches in diameter, and 1630 pounds, falling 3 feet 5 inches, to force out 6 inches of sand. Experiments, 60, 61, 62, and 63, showed that the apparatus in its then state could not sustain the force necessary to expel 7 inches of sand, and accordingly these experiments were suspended until a cast brass tube could be procured, and an iron chain be fitted instead of the rope. Other measures were also adopted for strengthening the apparatus. While these arrangements were making, a series of experiments were tried with a conical plug above the piston, as in the annexed sketch. The height of the cone was 3 inches, and its base equal to the area of the top of the piston. The details of these experiments it is deemed unnecessary to give. Their general result was, that within the limits tried, greater resistances were obtained when the cone was used than when it was omitted.