Floats of casks, when in bridge, should always be rigidly connected with each other at their ends by stringers, which must be lashed to both gunnels of each float; the roadway stringers can then be laid and should rest squarely on both gunnels of each float and should be lashed, especially if there be any sway or for animal traffic. TABLE OF WEIGHTS, DIMENSIONS, CAPACITY, ETC. --------+-------+---------+-------+-------+-----+--------- Name. |Weight.| Length | Bung | Head | No. |Available | |of Stave.| Diam. | Diam. |Gals.|Buoyancy. --------+-------+---------+-------+-------+-----+--------- | Lbs. | Inches. |Inches.|Inches.| | Lbs. | | | | | | (About). Tar | 50 | 30 | 20½ | 17½ | 30 | 250 Pork | 60 | 30 | 22 | 18½ | 32 | 267 Vinegar | 80 | 34 | 23½ | 20½ | 45 | 375 Whiskey | 80 | 34 | 23½ | 20½ | 45 | 375 Kerosene| 70 | 34 | 25 | 21 | 45 | 375 Molasses| 70 | 34 | 25 | 21 | 52 | 433 --------+-------+---------+-------+-------+-----+--------- American wine-barrels are about the same size and weight as whiskey-barrels. =Rafts.=--Raft bridges may be used in a current not exceeding four miles an hour. Cubic content of a log in feet is equal to the square of one fifth of the mean girth multiplied by twice its length. Weight of timber (dry) per cubic foot: Ash 47 lbs., beech 43, elm 36, fir 32, oak 54, pine 40, poplar 24, sycamore 37, willow 25. Green timber is about one fourth heavier. =Flotation.=--To obtain the flotation of a log, multiply its cubic content by the difference between its weight per cubic foot and the weight of a cubic foot of water (62½ lbs.). Take five sixths of the result for the available buoyancy. =To Form a Raft.=--Place the logs side by side, the small ends alternating; strongly secure with rope and, if possible, by cross and diagonal pieces of scantling fastened by spikes or treenails. If it is to be used as a pier, the logs may be placed in two layers to avoid obstructing the waterway. A central transom must be used. The up-stream end of the raft may, with advantage, be convex. =Make-shift Anchors.=--Two or more pickaxes lashed together; heavy weights, such as large stones or railway irons; the latter are best when bent. Nets filled with stones are particularly good on rocky bottoms. =Protection.=--Arrangements must be made up-stream to protect a floating bridge from damage from floating substances, either by a boat patrol, or by stretching a net, or some intercepting obstacle, across stream. CHAPTER XIII. Hasty Demolition. Gunpowder. Dynamite. How Used in Blasting. Guncotton. Rack-a-rock. Handling, Transportation, and Storage of High Explosives. Charges for Hasty Demolition. Where and How to Place Charges.