This process is effected by heating the metal in charcoal furnaces to a white incandescent glow, and then cooling it by immersion in baths of oil and other drugs, the combination of which is, we believe, a secret. This done, the saws are ready for grinding which is effected in a special apartment of the main building—the flat, straight saws by hand application to a series of powerful grindstones, driven at a regular speed by gearings worked from the engine, and the circular saws by a very curious and effective patent machine, peculiar to this establishment, and invented by Mr. Hoe himself. The old method of grinding circular saws, and that still practiced in all other works of this nature, is the application of them horizontally to the great vertically-moving grindstones by the hand; and, when it is considered that these great steel plates run up to six feet diameter and eighteen of circumference, and that they consequently entirely conceal the grindstone from the eyes of the operator who applies them, it will be evident that the process is mere guess-work, and that no certainty can be attained in regulating the thickness of the blades—in a word, that nothing was effected beyond the superficial brightening and abstersion of the surface. [Illustration: GRINDING ROOM.] The new machine causes the great circular plate to revolve vertically on its access, while a “pad” to which is applied some sharp, detergent mineral-powder, is moved forcibly over its surface with a triple action. In the first place, the pad itself is made to revolve with great velocity against the circular plane, in a direction perpendicular to its line of motion. In the second place, it is driven forward against it horizontally with a force increasing or diminishing, in proportion as it may be desirable to render the saw-blades thicker or thinner in any particular part of the circumference. It is usual to leave them thicker at the centre, and to grind them away gradually toward the circumference. Thirdly and lastly, the pad, while it revolves vertically in a direction perpendicular to the revolving plane, and is forced horizontally against it, is also driven laterally to and fro across its surface; and the result is a degree of equability, or graduation of thickness, as well as of superficial polish, scarcely otherwise attainable. This machine is one of the special wonders and ornaments of the establishment. It will not be amiss here to add, that with the improvements of their manufacture the demand for circular saws is continually on the increase; and that a single house is in the habit of taking regularly six of these powerful tools weekly from the Messrs. Hoes’ establishment. [Illustration: IRON PLANING, AND CUTTING ENGINE ROOMS.]