Buildings for manufacturing purposes next demand attention. Some time since a manufacturer and contractor for iron work remarked to me, that if some one would only put up a large fire-proof building, with good steam power, to be rented out for manufacturing purposes, his fortune would easily be made. I have often thought of the suggestion, and wondered why it had not been acted upon. He said that at that time it would be impossible to hire a fire-proof shop or room, with power, in this city. Now, there are many occupations requiring delicate, and not easily replaced machinery, or in which are involved elaborate experiments, running for long periods—the derangement of which could not be recompensed by any amount of insurance—for which a fire-proof building would be almost invaluable. The saving of insurance on such a building and its contents would be greater than the interest on the extra cost of fire-proof floors, and would enable the owner to rent his rooms at a lower rate—in proportion to the equivalent given—than could the owners of buildings with wooden floors. The extra cost of fire-proof construction in a manufacturing building is small when compared with that of a bank or public building. The walls and ceilings require neither lath nor furring, and the floors may be of flags or slate, bedded on the brick arches, or what is better, plates of cast-iron bolted to the beams—which will presently be described. All inside finish may be discarded, and iron doors, of No. 16 iron, with light wrought-iron frames, hung to stone templates in the jambs, are the only coverings required for the openings. Such fire-proof buildings as have been erected for manufacturing purposes have been specially designed for single occupants. The most perfect and the earliest that I know of is a building erected on Vestry street, about ten years since, for the Grocers’ Sugar Refining Company. This building, as far as its material is concerned, is absolutely fire-proof. It is most remarkable for its floors, which are made of plates of boiler-iron, riveted together and secured to the beams in large sheets. This is the most simple system of floor construction I have ever seen, and has many advantages. But I have not seen the building in use, and do not know how the floors answer the ends for which they are intended. Some of the new buildings for the various gas works in this city are fire-proof. The best are those of the Metropolitan Company, at the foot of Forty-second street, North river. But they are at best, only sheds—brick walls, with iron shutters and roofs. Large, open, and well ventilated, they serve their purposes well; but they can hardly be called architecture.