A Treatise On The Principles And Practice Of Harbour Engineering

PILING. 63 A splinter in the flesh almost invariably produces blood-poisoning, and the merest scratch should be promptly sucked and washed in clean water. The weight of greenheart ranges from 60 to 75 Ibs. per cubic foot, so that it has practically no flotation. This characteristic facilitates its mani- pulation for piling purposes, as it sinks readily into position. It can be obtained in balks from 12 to 24 inches square and up to 70 feet in length. It has an ultimate compressive strength, in short prisms, of 8 to 8| tons per square inch, and a beam of unit dimensions, i.e. 1 inch square in section and 1 foot between supports, will fail at loads ranging from 950 to 1500 Ibs., centrally and concentratedly applied. The colour of greenheart ranges from green to almost black. Purpleheart is a wood of the same kind, from the same locality, with a difference only in colour, as iudicated by the name. It is perhaps a little tougher and slightly more durable, but, on the other hand, it is not so readily procurable. Balks can be obtained up to 30 inches square. Mora (Afora excelsa) is also a native of Guiana, but is a light-red wood, with several distinguishing characteristics. It shares the strength and durability of greenheart, while it differs from it in possessing great toughness and in lacking any disposition to split or splinter. It is rather lighter in weight, too, than greenheart, weighing from 57 to 68 Ibs. per cubic foot. The Eucalyptus family is a numerous one, and indigenous to the Australian continent. Jarrah (Eucalyptus marginata) is a timber found in abundance in Western Australia, and, from its resemblance to mahogany, it is sometimes called Australian mahogany. It is hard, heavy, and close-grained ; very liable to warp and split. Tt is also beset with clefts filled with resinous matter, which is sometimes found to be in a state of decay. The fibres also contain an acid having a pungent odour. The tree grows to a height of 200 feet and more, but sound logs are limited to 40 or 45 feet in length and 12 to 24 inches square. The weight of jarrah is just about equal to that of an equal volume of water. It has little more than half the crushing strength of greenheart, and the ultimate transverse strength of a unit beam (1 inch square and 1 foot clear span) is between 500 and 650 Ibs., concentrated at the centre. Karri (Eucalyptus diversicolor) is a hard, heavy, straight-grained wood, with some claims to toughness. It is somewhat stronger than jarrah, but less durable in damp situations; though when totally and continuously im- mersed, it is said to last well. The Blue Gum (Eucalyptus globulus) and the Stringy Bark (Eucalyptus obliqua) are two varieties of the same species, which have latterly conie into use and have demonstrated considérable merit for staging purposes in con- nection with the improvement works at Dover Harbour. The former is so named from the characteristic glaucous blue tint of the young plant, though the colour of the mature wood is a golden yellow or brown. Both trees grow to an enormous height and girth, and furnish tough,