Page:Popular Science Monthly Volume 23.djvu/636

618 Experimental tests were made with several partition walls, to ascertain how thin it would be advisable to construct them where the load was small. The result of the experiments showed that the resistance of partitions eight feet in height made of béton two and a half inches thick, and re-enforced with one-quarter-inch iron rods, was equal to brick walls eight feet high, and eight inches in thickness.

It is the opinion of the writer that for the great majority of houses required for dwelling purposes, a system of thin re-enforced double walls, with a space of from six to ten inches between them, and re-enforced cross-connections every two or three feet apart, to unite the outer and inner walls firmly together, could be built up to thirty or forty feet in height, at a cost not exceeding that of first-class brickwork.

Besides an equal economy in the construction, such double walls would be an incomparably better defense against stormy weather than the best quality of brick-work, because the absorptive capacity of béton is so much less than that of brick.

Thus, all things considered, the thin double-wall system commends itself as embodying the desirable qualities, essential to the outer and inner wall construction of dwelling-houses, furnishing as it would a sure protection against both fire and dampness, and the means for thorough ventilation. Besides the special fitness of the re-enforcing system for floors, roofs, beams, and thin walls, it is an interesting question whether the same system may not be also applicable, and advantageously extended, to a more general use in many engineering requirements—especially in situations where immense weights must be sustained, and where iron construction alone is difficult of application; notably in such an important work as the Hudson River Tunnel, where its tubular form is constructed with an outer cylindrical shell of flue-iron, and lined inside with heavy brick mason-work. Much of this tunnel rests upon a treacherous bed of silt, and might be made absolutely safe from rupture by settling, induced by vibrations resulting from railroad traffic in addition to its own weight, by adding to a thin brick lining a strong béton sixteen or eighteen inches thick, which should include three or four courses of iron bars, of suitable size, laid longitudinally and in sufficient number to bear any amount of strain that might be brought upon it. Rings of flat bar-iron, interspersed in the béton-lining a few feet apart, would further add to its security.

The re-enforced béton system has also been employed with admirable results, in heavy foundations, for stationary engines. The writer, three years ago, mounted a two-hundred-and-fifty-horse-power, tandem, compound engine, of very heavy pattern, on a re-enforced béton-bed, twenty-three feet long, five feet wide, and seven feet deep. It is apparently as firm and hard as a single mass of granite of those dimensions. The outboard bearing of the main shaft is also mounted