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.