Brick-work . . . 110 Granite . . . 160 to 170 Portland stone . . 150.
We must refer to the report itself for more detailed infor mation on this subject, only adding the conclusion come to by the committee, that " there is not sufficient experience of the use of concrete to warrant its adoption for the faces of works to be constructed in the sea." The French engineers have made use of beton in many of the extensive works on the continent ; beton sets very rapidly under water, and attains, after a time, a very con siderable degree of hardness. M.Milet de Montville having filled a chest containing tri cubic feet of beton, sunk it in the sea, where it remained during two months, after which it was drawn lip, to ascertain the consolidation it had acquired. On inspection it was found to be converted into so compact a body, that Inure difficulty was experienced in separating its parts, than those of a block of hard stone. The best manner of compounding the beton, according to M. de Montville, is as follows :—`• Take twelve parts of pnzzolana, (lerrasse de Ilollande, or Cendre de Tourney,) of which form a circular wall of five or six feet in diameter, on which place six parts of sand, well sifted, free fioni earthy matter, and evenly spread. Fill the interior of this
circle with nine parts of quick-lime, well calcined, and pul verized with an iron beetle ; and to cause it to slack more quickly, (in maritime works) throw on sea-water in small quantities, stirring it from time to time with an iron spatula. As soon as it is reduced to a paste, incorporate the puzzolana and the sand. The whole being well mixed, throw in thir teen parts of mffiewn stone, and three parts of iron dross, well pounded. If this latter ingredient cannot be obtained, sixteen parts of rough stones or pebbles must be added, of a size not larger than a pullet's egg. Let this composition be well amalgamated for the space of all In Mr, after which it must be left in heaps to coagulate; for this purpose the space of twenty-tbur hours will be sufficient in slimmer or in warm climates, but in winter it often requires the space of three or four days. Observe to keep it protected from the rain, and not to use it until it has sufficiently hardened to require breaking with a pickaxe." The method of using the beton is either in blocks, or by means of a colliT or chest filled with the composition, lowered to the required depth, and there emptied.