Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/486

464 H A K B O U II 8 Table of Properties uf different kinds of llwh Nam-- Of Hooks - ? X in "., O A, J X V. 1! of 5J rT o X i* i i S X s. ^ 8 i ilo }?> Side of a Cube weighing One Ton in Loss of We glit by immersion in Sea Specific Gravity. Weight of a Cubic Foot in Air. No. of Feet to a Ton in Air. No. of Feet to a Ton in Sea Water, Sp. Gr. 1 028. Side of Cube correspond ing to last column. Weight of a Ton Block in Sea Water, Sp. Gr. l-O-. S. Basalt (porphvritic) . 2 99 ft. 186 87 Cubic feet. 11 9 Cubic feet. 1 8 9 6 Lineal feet. 9-63 Ton. (JoS Feet. 2 "283 340 Greenstone 2 92 182-50 12 -2 19 00 2 66 650 2 30-> 50 Syenite 2 91 181-9 12 3 19-04 2 67 647 2 308 353 Clay-slate 2 90 181-25 12 3 19-15 2 67 647 2 308 353 Mica-schist .... 2 89 120-6 12 4 19 24 2 68 644 2-315 Gneiss 2 82 176-2 12 7 20 -00 271 635 2-333 365 Amyoxlaloidal greenstone 275 171-87 13-0 20-81 2 75 627 2 351 373 Chlorite-selmt Grey waclce 274 2 73 171-25 170-62 13-0 13-1 20-93 21-06 2-75 276 627 624 2-351 2-357 373 376 Clinkstone 2-73 170-62 13-1 21-05 2 76 624 2 357 376 Red granite 271 169-37 13 2 2T30 2 77 621 2 362 379 Slate (Old Red Sandstone formation).... Chalk . 2-71 2 70 169-37 168-75 13-2 13 2 21-30 21 43 2-77 2 77 621 621 2-362 2 S62 379 379 White Primary limestone (marble) 270 168 75 13 2 21 43 2 77 621 2-362 Red Primary limestone (marble), with / crystals of au^ite embedded 2-C6 166-25 13-4 21-96 2 80 61 5 2-375 385 Chlorite slate 2 64 165-00 13-5 22-23 2 81 612 2-381 388 Granular quartz rock 2 63 164-37 13 6 22 37 2 82 010 2 387 390 Grey granite 2 61 1 63 -1 2 13 6 22 65 2 83 610 2-387 390 Flinty slate 2-57 160-62 13 9 23-24 2 85 601 2-405 399 Red felspar porphyry 2-55 159-37 14-0 23 55 2 86 598 2-410 402 Pitchstonc 2 53 158-12 14 1 23 86 2 88 595 2-416 405 Serpentine 2-46 153-75 14 5 25-02 2 92 584 2-438 416 Compact felspar 2 45 153-12 14 6 25-20 2 - 93 581 2-444 419 Sandstone 2-41 150-62 14-8 26-00 2 96 "575 2-455 425 Roestone (Oolite) 2-36 147-50 15-1 26-88 2-99 567 2-472 433 Beton 2 2 137 OS 16 3 30 6 3-13 532 2-535 468 Masrnesian limestone .. ... 2 18 136-25 16 4 31-11 3-14 529 2-541 471 Oolite 2-05 128-12 17 4 35-07 3 27 501 2-591 499 Parrot coal (America!)) 1-54 96 25 23 3 70-00 4 12 2-856 669 Bituminous shale 1 50 93-75 23 8 75-93 4 23 317 2-876 683 Cannel coal 1-24 77 50 28 9 169-05 5-53 171 S 069 829 NOTE. This table is calculated for sea water of the from the manufactory and kept at the works in a dry and well- ventilated storehouse with dry wooden floor and side walls, pro perly roofed in and completely protected from the weather. The concrete to be used is to consist of one part of Portland cement, two of sand, and five of gravel, to be thoroughly mixed with a proper quantity of pure water ; after it is deposited, large angular stones are to be added, care being taken that all the stones are completely surrounded by concrete for a thickness of not less than 4 inches. All stones to be clean and quite free from sea-weed or other vege table matter likely to prevent the adhesion of the concrete. No concrete to be made during frost. The sand and gravel used must be sharp and clean, being perfectly free from clay or earthy matter. There are different kinds of machines by which the concrete is thoroughly mixed, and a saving of cost effected. In that of Mr Messent the number of revolutions to mix the concrete thoroughly is twelve. 2on- The walls of harbours may be constructed of continuous tinuous building of concrete and stones, protected by temporary building. pii[ n g anc l dose planking. The best mode of keeping out the water, as adopted by Mr Balmer at the duke of Rich mond s harbour of Port Gordon, is to make a saw-draft in each plank, and to place a thin plate of iron between the planks. An example of this continuous or monolithic, building is shown in Plate VIII., fig. 6. Mr B. B. Stoney has deposited at Dublin the largest blocks that have as yet been attempted to be moved. Each block is 27 feet high, 21 feet 4 inches wide at base, and 12 feet long in the direction of wall, contains nearly 5000 cubic- feet, and weighs 350 tons ; and when laid in place 12 lineal feet of the wall is finished at once up to ordinary low water level. No cofferdam, staging, or pumping is required. The superstructure^ built in the ordinary method by tide work, and is facet! with granite ashlars for the ships to lie against. The blocks are built on land, and after 10 weeks drying are lifted by floating shears, the barge or pontoon of which is 120 feet long and 48 feet wide, and of this 130 specific gravity of 1/028 or 64j Ib to the cubic foot. feet 30 form a tank at the aft end ; and, when filled with water, this balances the weight of the block hanging from the shears at the other end. A block can be raised with the flood tide, and is gene rally set the following low water. The late Mr J. M. Rendel introduced the improved and very valuable method of depositing the pierres perdues or rubble, which is now generally used in the construction of large breakwaters. This method he employed first at Millbay pier, near Plymouth, in 1838, in a depth of 38 feet, and afterwards, on a still larger scale, in the con struction of the breakwaters at Holyhead and Portland. The improvement consists in depositing the rough materials from stagings of timber, elevated a considerable height above high water. The stones are brought on the staging in waggons, through the bottoms of which they are discharged into the sea. The principle on which these stagings are designed is that .of offering the smallest possible resistance to the sea, the under structure consisting of nothing more than single upright piles for supporting each roadway. At Wick harbour works, as already stated, it was found that the piles of the staging for depositing the rubble required to be cf greenheart timber; but even these were broken in large numbers. The piles were invariably broken by the waves at about the level of high water. A depth of from 12 to 15 feet under low water was pointed out by Mr Eendel as the level below which the waves did little or no damage to pierres perdues. Sir John Rennie indeed considered that there was little or no effect at a fathom and a half. But at Wick, as already stated, the rubble was moved as low as 15 feet, and at Alderney 20 feet. If the beds of the stones in a sea-wall were polished, the power of resistance would be reduced by about one-fourth, or in other words, roughly dressed materials of three-fourths the weight of polished materials will be equally safe. Depo: ing piem perdu Level conse vatio rubbl Evil fine

dress