No mode, however, has yet been devised for dispensing with the operation of grinding in the case of the barrel; though the injury to the health is much less in this case than in the other.
BURSTING OF GRINDSTONES
There is another very formidable danger connected with the process of grinding besides the insalubrity of the work; and that is the danger of the bursting of the stones in consequence of their enormous weight and the immense velocity with which they are made to revolve. Some years since a new method of clamping the stone, that is of attaching it and securing it to its axis, was adopted, by means of which the danger of bursting is much diminished. But by the mode formerly practiced – the mode which in fact still prevails in many manufacturing establishments where large grindstones are employed – the danger was very great, and the most frightful accidents often occurred. In securing the stone to its axis it was customary to cut a square hole through the centre of the stone, and then after passing the iron axis through this opening, to fix the stone upon the axis by wedging it up firmly with wooden wedges. Now it is well known that an enormous force may be exerted by the driving of a wedge, and probably in many cases where this method is resorted to, the stone is strained to its utmost tension, so as to be on the point of splitting open, before it is put in rotation at all. The water is then let on, and the stone becomes saturated with it – which greatly increases the danger. There are three ways by which the water tends to promote the bursting of the stone. It makes it very much heavier, and thus adds to the momentum of its motion, and consequently to the centrifugal force. It also makes it weaker, for the water penetrates the stone in every part, and operates to soften, as it were, its texture. Then finally it swells the wedges, and thus greatly increases the force of the outward strain which they exert at the centre of the stone. When under these circumstances the enormous mass is put in motion, at the rate perhaps of five or six revolutions in a second, it bursts, and some enormous fragment, a quarter or a third of the whole, flies up through the flooring above, or out through a wall, according to the position of the part thrown off, at the time of the fracture. An accident of this kind occurred at the Armory some years since. One fragment of the stone struck the wall of the building, which was two or three feet thick, and broke it through. The other passing upward, struck and fractured a heavy beam forming a part of the floor above, and upset a work-bench in a room over it, where several men were working. The men were thrown down, though fortunately they were not injured. The workman who had been grinding at the stone left his station for a minute or two, just before the catastrophe, and thus his life too was saved.
POLISHING
We have said that the grinding room is the only dangerous room in such an establishment as this. There is one other process than grinding which was formerly considered as extremely unhealthy, and that is the process of polishing. The polishing of steel is performed by means of what are called emery wheels, which are wheels bound on their circumference by a band of leather, to which a coating of emery, very finely pulverized, is applied, by means of a sizing of glue. These wheels, a large number of which are placed side by side in the same room, are made to revolve by means of machinery, with an inconceivable velocity, while the workmen who have the polishing to do, taking their stations, each at his own wheel, on seats placed there for the purpose, and holding the piece of work on which the operation is to be performed, in their hands, apply it to the revolving circumference before them. The surface of the steel thus applied, receives immediately a very high polish – a stream of sparks being elicited by the friction, and flying off from the wheel opposite to the workman.
Now although in these cases the workman was always accustomed to take his position at the wheel in such a manner as to be exposed as little as possible to the effects of it, yet the air of the apartment, it was found, soon became fully impregnated with the fine emery dust, and the influence of it upon the lungs proved very deleterious. There is, however, now in operation a contrivance by means of which the evil is almost entirely remedied. A large air-trunk is laid beneath the floor, from which the air is drawn out continually by means of a sort of fan machinery connected with the engine. Opposite to each wheel, and in the direction to which the sparks and the emery dust are thrown, are openings connected with this air-trunk. By means of this arrangement all that is noxious in the air of the room is drawn out through the openings into the air-trunk, and so conveyed away.
The sparks produced in such operations as this, as in the case of the collision of flint and steel, consist of small globules of melted metal, cut off from the main mass by the force of the friction, and heated to the melting point at the same time. These metallic scintillations were not supposed to be the cause of the injury that was produced by the operation of polishing, as formerly practiced. It was the dust of the emery that produced the effect, just as in the case of the grinding it was the powder of the stone, and not the fine particles of iron.
The emery which is used in these polishing operations, as well as for a great many similar purposes in the arts, is obtained by pulverizing an exceedingly hard mineral that is found in several of the islands of the Grecian Archipelago, in the Mediterranean. In its native state it appears in the form of shapeless masses, of a blackish or bluish gray color, and it is prepared for use by being pulverized in iron mortars. When pulverized it is washed and sorted into five or six different degrees of fineness, according to the work for which it is wanted. It is used by lapidaries for cutting and polishing stones, by cutlers for iron and steel instruments, and by opticians for grinding lenses. It is ordinarily used in the manner above described, by being applied to the circumference of a leathern covered wheel, by means of oil or of glue. Ladies use bags filled with it, for brightening their needles.
Emery is procured in Spain, and also in Great Britain, as well as in the Islands of the Mediterranean.
PROVING
When the barrels are brought pretty nearly to their finished condition, they are to be proved, that is to be subjected to the test of actual trial with gunpowder. For this proving they are taken to a very strong building that is constructed for the purpose, and which stands behind the Stocking Shop. Its place is on the right in the general view of the Armory buildings, and near the foreground – though that view does not extend far enough in that direction to bring it in. The exterior appearance of this building is represented in the above engraving. It is made very strong, being constructed wholly of timber, in order to enable it to resist the force of the explosions within. There are spacious openings in lattice work, in the roof and under the eaves of the building, to allow of the escape of the smoke with which it is filled at each discharge; for it is customary to prove a large number of barrels at a time. The barrels are loaded with a very heavy charge, so as to subject them to much greater strain than they can ever be exposed to in actual service. The building on the left, in the engraving, is used for loading the barrels, and for cleaning and drying them after they are proved. The shed attached to the main building, on the right hand, contains a bank of clay, placed there to receive the bullets, with which the barrels are charged.
The arrangement of the interior of this building, as well as the manner in which the proving is performed, will be very clearly understood by reference to the engraving below.
On the right hand end of the building, and extending quite across it from side to side, is a sort of platform, the upper surface of which is formed of cast-iron, and contains grooves in which the muskets are placed when loaded, side by side. A train of gunpowder is laid along the back side of this platform, so as to form a communication with each barrel. The train passes out through a hole in the side of the building near the door. The bank of clay may be seen sloping down from within its shed into the room on the left. The artist has represented the scene as it appears when all is ready for the discharge. The barrels