I have not made any reference to the use of rolled iron for structural purposes, because such material has not been used to any extent in mill architecture. Irrespective of questions of space or of strength, wood beams possess advantages in the reduction of vibration, facility of securing the plank above and hangers below, and a great many other purposes in the changing and alterations of a mill, which render them peculiarly useful, and I believe that the results with Southern pine beams in American mills are much superior to those of the iron beams in European mills.
No small part of the success attending the use of rolled iron in the structural purposes for which it is adapted, has been due to the excellent and reliable engineering information contained in the manuals and catalogues issued by the rolling mills. Such works are reliable and clear, and, as far as I know, can without exception be safely followed.
The general tendency of American mill construction is toward as low buildings as the price of land will admit. The American mills being devoted to a large variety of operations, instead of being confined to a single process after the manner of those of European type, require a great deal more care in their organization, not merely in the original lay-out for the purpose of arranging for the passage of the stock in processes from the raw material to the finished product in as straight lines as possible, but due consideration should also be given to providing facilities for the enlargement of the mill.
As an illustration of the methods employed, in a paper mill plan of my own design, [the view and plan being thrown on the screen], the various operations containing processes of different hazard in regard to fire are completely isolated from each other by means of fire walls, and the storage of the mill is in turn isolated from the manufactory.
The storehouse consists of three sections, the largest section for paper stock, which is sorted in the upper story, the second section, one story in height, for other manufacturing supplies, and beyond the fire wall the storehouse is arranged to contain the finished paper. Goods can be taken away from or added to the storehouse at the single line of teams, or railroad siding.
After the stock leaves the sorting room, it is carried to the dusting room over a covered bridge, which is protected from the weather on one side, yet does not form a flue for the spread of fire as does a closed bridge.
The first room in the main mill is used for a dusting room, and thence the stock falls into the rotary bleach, whence it is carried through the fire doors to the engine room. Here it meets the wood pulp and clay wheeled from the middle section of the storehouse, which is on that same level. After washing and beating, the stock is run into the drainers below, whence it is raised again, and after suitable intermediate processes the pulp is converted into paper on the paper machine in the connecting building. This paper is then taken into the upper part of the main building, and after being dried on the lofts is suitably calendered and packed before being transferred into the extreme end of the storehouse to await shipment.
At the present time it has been found that an inclined roof of the olden type is not a necessity over a paper machine, as has been decreed by the tradition passed down from old practices. Within the last year, a number of flat roofs have been placed over paper machines, without any trouble ensuing from condensed water forming on the ceiling and thence dropping upon the stock. It is well known that the use of a flat roof in such places is attended with a great many mechanical conveniences; and the pitched roof hitherto used for these purposes has been submitted to, only because it was presumed to be necessary. The whole tendency of mill design is in the line of fitness of means to ends, in the simplest and most direct manner.
When the mills in Lowell were first built, they consisted of isolated buildings, which it was presumed would remain for all time; but when it became necessary to increase the plant, it was found that the engineer had wisely laid out the mills in the same yard in reference to a fixed grade, so that corresponding floors would meet when the buildings were extended so that they reached each other.
Wherever a strong and diffused light is necessary for any manufacturing process, or the conditions are such as to require unusual stability of the building, one-story mills lighted by monitors afford accommodations not reached by any other form of construction.