Constructing the Float.—Having determined on the number of casks to be united in one float, take one third the number and place them transversely on two poles laid on the ground parallel to each other and one half the height of a cask apart; the casks to be distributed evenly over a distance equal to the width of the proposed bridge, bungs up. Lay another pair of poles on the top of the casks, and lash them to the first pair at the ends and between each two casks, and cut off any surplus pole that may project at the ends. Having made and launched three such floats, unite them by lashing a pole across the ends and middle of them, so as to make a large square raft. When enough such rafts are completed, they can be placed, and a roadway built on them. In placing the rafts the sides of the barrels should be towards the current.

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
of Stave.		Bung
Diam.		Head
Diam.		No.
Gals.		Available
Buoyancy.
Lbs.Inches.Inches.Inches.Lbs.
(About).
Tar503020½17½30250
Pork603022 18½32267
Vinegar803423½20½45375
Whiskey803423½20½45375
Kerosene703425 21 45375
Molasses703425 21 52433

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.