It would seem too, at first thought, that this operation of grinding must be a very safe as well as a simple one; but it is far otherwise. This grinding room is the dangerous room—the only dangerous room, in fact, in the whole establishment. In the first place, the work itself is often very injurious to the health. The premises are always drenched with water, and this makes the atmosphere damp and unwholesome. Then there is a fine powder, which, notwithstanding every precaution, will escape from the stone, and contaminate the air, producing very serious tendencies to disease in the lungs of persons who breathe it for any long period. In former times it was customary to grind bayonets as well as barrels; and this required that the face of the stone should be fluted, that is cut into grooves of a form suitable to receive the bayonet. This fluting of the stone, which of course it was necessary continually to renew, was found to be an exceedingly unhealthy operation, and in the process of grinding, moreover, in the case of bayonets, the workman was much more exposed than in grinding barrels, as it was necessary that a portion of the stone should be open before him and that he should apply the piece in hand directly to the surface of it. From these causes it resulted, under the old system, that bayonets, whatever might have been their destination in respect to actual service against an enemy on the field, were pretty sure to be the death of all who were concerned in making them.
The system, however, so far as relates to the bayonet is now changed. Bayonets are now "milled," instead of being ground; that is, they are finished by means of cutters formed upon the circumference of a wheel, and so arranged that by the revolution of the wheel, and by the motion of the bayonet in passing slowly under it, secured in a very solid manner to a solid bed, the superfluous metal is cut away and the piece fashioned at once to its proper form, or at least brought so near to it by the machine, as to require afterward only a very little finishing. This operation is cheaper than the other, and also more perfect in its result; while at the same time it is entirely free from danger to the workman.
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.