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almost always between thirty and thirty-three degrees; it rarely maintains itself at thirty-five degrees.
In a well sifted heap, the inferior layers, themselves inclined at thirty degrees with the horizon, serve naturally as supports to the superior ones; but the greater part of the weight of these latter, is supported by the portion of the horizontal plane against which they terminate or abut. If we take away this portion of the horizontal plane or bottom, these outer layers immediately roll off, leaving those on which they rested, undisturbed and inclined under an angle of from thirty to thirty-three degrees. This explains why sand does not flow out of a horizontal opening, if the thickness of the body through which the opening is pierced, is equal to or greater than the height, or vertical dimension of the orifice. In this case the superior layers find points of support on the sides of the containing vessel, and an absolute obstacle in the inferior layers.
Is this property connected with the form of the grains of which the sand is composed? If they had more regularity we might conjecture so, but upon looking at them through a microscope, we see such a variety of figures and dimensions that it is impossible to admit this idea. The greater part of the grains are crystalline laminæ, white, flattened and variously terminated; other particles are grey, yellow, brown, &c. with such different forms that they cannot be arranged into distinct classes.
In order to decide whether the form was of any importance in the arrangement of the parts, I tried other substances besides sand, and found that peas or small shot, although with a little more difficulty in forming them into slopes, took nearly the same angle, and followed in all respects the same laws.
II. Pressure of Sand and other Substances composed of Grains.
1. An egg having been placed at the bottom of a box and covered with several inches of sand, the sand was loaded with a mass of iron weighing fifty-five pounds. The result was precisely what I had anticipated; the egg remained unbroken under the great weight which was placed above it.
I repeated this experiment, putting the sand in motion by means of an orifice at the bottom of the box. The result was the same, whether the egg was placed at the bottom or in the middle of the mass of sand.
These trials proved that the pressure excited by the mass of iron was deflected laterally by the interposition of the sand. They proved also, that a body placed in a mass of sand, is protected by it as it would be by a liquid, although the sand has a different kind of action from the liquid, on the sides of the vessel containing it.
These conclusions being somewhat paradoxical, I resolved to have recourse to more decisive proof.
2. I took a tube of glass open at both ends, and inserted it, vertically into a small horizontal tube of wood near one end, the other end of this horizontal tube being exactly fitted into a vertical cylindrical box
ths. of an inch in diameter and eight inches in height.
I filled this box with mercury, as if it had been the cistern of a barometer; the mercury naturally assumed its level in the vertical tube of glass. Its height in this tube was marked. I then adapted to the box, or cylindrical cistern, a large tin tube twenty-seven inches long, and one inch and onethird in diameter. I filled this large tube with sand, taking care to pour it in very slowly, so as not to agitate the mercury.
Here was a true barometer for measuring the weight of the sand; there
was an equal pressure of air on each side, so that apparently nothing prevented the equilibrium between the sand and the mercury. Although I had in part expected the result, I was surprised to see that the sand had added nothing to the weight of the mercury; the liquid kept its level to within 1th. of an inch, a difference which was produced by an accidental shaking of the apparatus during the experiment; for having changed the place of the apparatus, the mercury resumed its level as before the experiment, and preserved it as long as I maintained this state of things.*
I afterwards took the sand from above the mercury; it had not penetrated into the liquid. I substituted in its place dried peas; the large tube was completely filled with them, their weight being more than three pounds. I added an iron weight of upwards of two pounds, and lastly a pressure of the hand as great as I durst apply without endangering the apparatus. The mercury kept its level in the glass tube; not rising th. part of an inch. The apparatus remained several days on trial without any other result. Thus the mercury had not been acted on by the weight of the sand, nor by that of the peas.
This absence of pressure on the bottom of a vessel was still better proved by the following experiments.
3. I took the same tube of tin and suspended it from a very sensible balance; I counterbalanced it exactly, and arranged it so that it reached nearly to the floor. I placed on the floor itself, a small solid cylinder of wood, about two inches high, and a little less in diameter than the large tube, so that the tube inclosed the cylinder, and could play freely in a vertical direction. As the tube was perfectly equipoised, and suspended to the arm of the balance vertically above the small solid cylinder, it moved upwards and downwards along this latter without any sensible friction.
I next weighed out a quantity of dried peas and introduced them into the large tin tube. It lost its mobility instantly, as if it had become more heavy, notwithstanding that it had no bottom, and the peas had a solid support on the top of the cylinder of wood.
I afterwards put into the opposite dish of the balance a certain number of grammes successively, until the dish descended, when the tube separated from the cylinder, allowing the escape of the peas which it had contained.
The weight required to raise the tube from the top of the cylinder was, within a very few grammes, equal to the weight of dried peas which I had poured into the tube; the difference was not more than twenty grammes, whilst the weight of the peas was more than three and a quarter pounds. The tube, therefore, appeared to be loaded with all the weight of the peas to which it gave its support.
The experiment repeated with different quantities and with additional weights always succeeded, and often within eight or ten grammes.
But it might be still objected that the lower cylinder had in some way supported the weight of the column. I therefore made the inverse experi
4 and 5. In this experiment I fastened the tube by two cords to two supports laterally, and suspended the small cylinder from the dish of the balance, in such a way that being equipoised before hand, it was introduced freely half an inch into the tin tube, and by the least additional weight it fell and permitted the escape of its load.
The experiment would have been more simply made with a tube bent like a syphon with parallel branches; but M. Burnand had none at his disposal.
I then poured about three and a quarter pounds of peas into the tube, and finding that the wooden cylinder which was perfectly free, did not fall, I added a weight of two and a quarter pounds and other weights, without even moving it. It might still be objected, however, that the small cylinder adhered to the sides of the tin tube. To answer this objection, and to render this experiment more striking, I removed the cylinder, and made use of a simple disk of wood of greater diameter than the tube, and supported against its bottom by placing in the balance just weight enough to keep the two in contact. This weight was commonly from ten to twelve grammes.
I then filled the large tube with from three to four pounds of sand, and placed additional weights upon the top of the column, nevertheless the disk, retained by the small counterpoise of ten or twelve grammes, did not move. If this same weight of a few grammes had been laid on that part of the disk which projected beyond the tube, it would without doubt have caused it to fall, for it alone retained the disk in its place. A slight touch of the finger, caused the sand to pour from the lower end of the tube, and fall into a basin placed below to receive it. The disk was therefore instrumental in retaining the sand, but did not sustain the weight of it, which was all transferred to the sides of the large tin tube. Ten grammes would have caused this disk to separate from the tube, and since it remained adhering to it, the disk was not loaded with the mass of the sand.
6. To remove all kind of doubt, I gave up the use of the balance, and placing a tub of water near the large fixed tube, floated the disk of wood on the water with the smooth side upwards; I then brought the end of the tube down upon the disk, and poured water into the tub. The disk was pressed by the weight of the water against the end of the tube. I next filled the tube with dried peas but the disk did not move. It, however, was essential in retaining the peas, which without it would have fallen through the tube; but the peas did not press upon it, since a very small force would have sufficed to make them fall from the tube and thus derange the whole apparatus.
7. Leaving every thing in the same condition, I poured water into the large tube; it was kept there with the peas, for a considerable time, until an unforseen motion produced by the compressed air, which was disengaged from the bottom of the tube, caused the machine to incline. The peas then escaped into the tub, and the water flowed out at the same time. The same trial was made with sand; a considerable quantity of water was poured on the sand, fully impregnating it, and during a very long time it was supported without flowing out.
In another trial made a little differently, the sand took such a consistence with the water that it caused much trouble to get them out of the tube, which therefore entirely supported the weight of the sand and of the water, together with the force necessary to expel them.
8. We can make these experiments by simply causing the large tube to rest on a small conical heap of sand, whilst it is still suspended from the disk of the balance. The sand does not escape when the weight put into the other disk is nearly equivalent to the weight of the tube and its
The same trials succeeded with grain: I have repeated them with shot with equal success, although this has a very great weight. They may also be made with a simple roll of paper tied with two small strings; they are then much more striking as the weight acquired by the paper tube contrasts better with its original lightness.
9. I have repeated these experiments with a tin tube widened at the bottom and much larger than the great tube; the result was the same, although there can be no doubt that there is a limit beyond which the sand would receive no further support, from the sides of the tube. This will be the case when the inclination of these sides to a horizontal plane is the same as the slope assumed by sand in a heap, that is to say about thirty degrees. I have also repeated several of these trials with a cylindrical tube four inches in diameter, with the same success.
10. From all that I had seen I presumed that it would be very difficult to force sand through a tube even by means of a direct pressure. I made the trial in the following manner. I filled the great tube with sand and laid it in a horizontal position, and with a cylinder of wood, several feet in length, and a little less in diameter than the tube, endeavored to force out the sand at one end by pressing it at the other, but without success. It appeared to me that it would be easier to burst the tube than to move the sand a single inch. The tube being inclined to the horizon about twenty degrees, and the effect being thus aided by the weight of the body, the sand still could not be expelled; the same result followed in inclining the tube in the contrary direction. This explains very clearly why a blast confined with sand is as effectual as any other.
Ynerduv, 15th January 1829.
P. S. If in the experiment in section 2, under the head of the pressure of sand, we pour water into the tube which contains the peas, the mercury will rise in the glass tube one-fourteenth of the height of the water; a proportion which corresponds with that of the specific gravities of those liquids. The water acts as usual, but the peas exert no pressure.
2nd. There is another way of making the experiment with the tube which is within the reach of every body. Procure a tin tube an inch in diameter and as long as is desired, open at both ends. Take a sheet of fine paper and apply it against the end of the tube pressing up the edges with the hand so as to make it take its form; then moisten the edges of the paper with water and cause them to adhere to the sides of the tube. Place the end on a table and fill the tube with sand. Raise it with care, and notwithstanding the slight adherence of the paper, the sand will be sustained while the tube is freely moved about.
Srd, It would be desirable to place a vessel of sand provided with an orifice for its escape, under an air pump, in order to determine whether the velocity would be affected by its flowing in a vacuum.
(TO BE CONTINUED.)
[Biblioth. Univ. XL, 22.
POR THE JOURNAL OF THE FRANKLIN INSTITUTE.
On the Manufacture of Military Projectiles, Translated from the French of F. J. Culmann, Chef d'escadron d'artillerie, &c. &c. by ALFRED MORDECAI, Captain United States Ordnance Department.
The principal objects of this article are to point out certain faults in the manufacture of projectiles, and to indicate the means of giving them an even surface, an accurate eye, a thin seam, exact dimensions and perfect sphericity: on these points no detail will be neglected, but we shall not dwell on the description of processes which are well known in founderies.
Of the Iron used for casting Projectiles.
The kind of cast iron of which the best hollow projectiles are made is that obtained from very fusible ore, reduced with charcoal in furnaces of small elevation, at a medium heat, or by working the furnace in such a manner that the metal may be well mixed, inclining more towards a lamellar white metal than to grey, so that the laminæ, marked with greyish spots, may still be distinguished in it. The surface of a projectile made of this metal, which is very liquid, is perfectly smooth and free from flaws and holes, which is not the case with those made of grey metal, particularly of that which does not run freely. Metal inclining to white cannot be obtained with certainty from refractory ores, nor even from fusible ores if reduced with coke, or in furnaces of a certain height: this metal is moreover unsuitable for the manufacture of other articles, even for that of solid projectiles. In general, therefore the production of it is not desirable, and when accidentally obtained, it can seldom be used, because the projectiles made from it are too small; white cast iron, or that which inclines to white, shrinks more in cooling, or else at the instant of becoming solid, it expands less than the grey metal. In order to employ it usefully, therefore, the dimensions of the mould must be adapted to the properties of this kind of iron. It may also be doubted whether this brittle iron presents a sufficient resistance to the force of the powder, to prevent the projectile from being broken in leaving the piece, and to enable it to give, in certain cases, large fragments moving with sufficient velocity. It is used however in one of the iron districts of France, and with excellent results.
For the casting of hollow projectiles it is of little consequence whether the metal be good or bad, with reference to the quality of the fine iron obtained from it. It may even be said that the metal which produces a brittle iron, and which is generally very liquid, is better suited for this purpose than that which produces tough iron, provided that its bad quality does not proceed from the presence of too much silex, which would cause cracks and
Castings which are to be very dense and solid, and of a medium thickness should not be made from the crude iron of coke furnaces, when it contains a large proportion of earthy minerals: a portion of the latter is thrown out when the metal is cooled by exposure to the air, and this causes flaws in the interior resembling rents; and when this metal is cooled without exposure to the air, interior crystallizations are formed, which also produce flaws. These phenomena, arising from unequal cooling, seldom occur if the castings are either very large or very thin; in the former case the metal being very liquid, heats the mould and then cools nearly at the same time throughout the mass; in the latter, the cooling is almost instantaneous.
Metal which does not contain a large proportion of earthy minerals has no tendency to form these crystallizations; an appearance which resembles them at first sight is sometimes produced by lamina of graphite which in the cooling of the metal, collect in the interior of the mass. Crystallizations are frequently met with in the white grained metal, (when it is not produced by an overcharge of ore,) as well as in all kinds of grey-iron which contain earthy minerals.* Unless we have the exclusive use of a furnace, the di
These crystalline forms, so common in bombs, rarely occur in twenty-four pound howitzes, or in flasks. Out of thirty-eight ten inch and twelve inch shells, rejected for other reasons, which I have had broken, one third presented, in the fracture, crystallizations coloured yellow, crimson, &c. In six inch howitzes, we find rents produ