Strength of iron-cables compared to hemp cables:—
| Iron Cables. Diameter of Iron Rod. | Hemp Cables. Circumference of Rope. | Resistance. | ||
|---|---|---|---|---|
| Inches. | Inches. | Tons. | ||
| 0 | 7⁄8 | 9 | 12 | |
| 1 | 10 | 18 | ||
| 1 | 1⁄8 | 11 | 26 | |
| 1 | 1⁄4 | 12 | 32 | |
| 1 | 5⁄16 | 13 | 35 | |
| 1 | 3⁄8 | 14 | to 15 | 38 |
| 1 | 1⁄2 | 16 | 44 | |
| 1 | 5⁄8 | 17 | 52 | |
| 1 | 3⁄4 | 18 | 60 | |
| 1 | 7⁄8 | 20 | 70 | |
| 2 | 22 | to 24 | 80 | |
It would be imprudent to put hemp cables to severer strains than those indicated in the preceding table, drawn up from Brunton’s experiments; but the iron cables of the above sizes will support a double strain without breaking. They ought never in common cases however to be exposed to a greater stress. A cable destined for ships of a certain tonnage, should not be employed in those of greater burden. Thus treated it may be always trusted to do its duty, and will last longer than the ship to which it belongs. A considerable part of this decided superiority which iron cables have over hemp ones, is undoubtedly due to the admirable form contrived by Brunton. Repeated experiments have proved that his cables possess double the strength of the iron rods with which they are made—a fact which demonstrates that no stronger form can be devised or is in fact possible.
One of the most valuable qualities of iron cables is their resisting lateral as well as longitudinal strains as explained under [figs. 219.] and [221.]
Vessels furnished with such cables have been saved by them from the most imminent peril. The Henry, sent out with army stores during the peninsular war, was caught on the northern coast of Spain in a furious storm. She run for shelter into the Bay of Biscay among the rocks, where she was exposed for three days to the hurricane. She possessed fortunately one of Brunton’s 70 fathom chain cables, which held good all the time, but it was found afterwards to have had the links of its lower portion polished bright by attrition against the rocky bottom. A hemp cable would have been speedily torn to pieces in such a predicament.
In the contracts of the Admiralty for chain cables for the British navy, it is stipulated that “the iron shall have been manufactured in the best manner from pig iron, smelted from iron-stone only, and selected of the best quality for the purpose, and shall not have received in any process whatever subsequent to the smelting, the admixture of either the cinder or oxides produced in the manufacture of iron; and shall also have been puddled in the best manner upon iron bottoms, and at least three times sufficiently drawn out at three distinct welding heats, and at least twice properly fagotted.”
The following is a table of the breaking proof of chain cables, and of the iron for the purpose of making them, also of the proofs required by her majesty’s navy for chains.
| Size of Bolt. | Proof of Bolt. | Proof of Chain. | Navy Proof of Chain. | ||||
|---|---|---|---|---|---|---|---|
| Inches. | Tons. | Cwt. | Tons. | Cwt. | Tons. | ||
| 1⁄2 | 5 | 7 | 8 | 11 | 4 | 1⁄2 | |
| 5⁄8 | 8 | 7 | 13 | 4 | 5 | 1⁄2 | |
| 3⁄4 | 12 | 1 | 19 | 5 | 10 | 7⁄8 | |
| 7⁄8 | 16 | 4 | 26 | 5 | 13 | 3⁄4 | |
| 1 | 21 | 8 | 34 | 5 | 18 | ||
| 1 | 1⁄8 | 27 | 2 | 48 | 15 | 22 | 3⁄4 |
| 1 | 1⁄4 | 33 | 10 | 53 | 11 | 28 | 1⁄2 |
| 1 | 3⁄8 | 40 | 10 | 65 | 0 | 34 | |
| 1 | 1⁄2 | 48 | 4 | 77 | 0 | 40 | 1⁄2 |
| 1 | 5⁄8 | 56 | 11 | 90 | 10 | 47 | 1⁄2 |
| 1 | 3⁄4 | 65 | 12 | 105 | 0 | 55 | 1⁄8 |
| 1 | 7⁄8 | 75 | 6 | 120 | 10 | 63 | 1⁄4 |
| 2 | 85 | 14 | 137 | 0 | 72 | ||
| 2 | 1⁄8 | 96 | 15 | 155 | 0 | 81 | 1⁄4 |
In Brunton’s cable the matter in the link is thrown very much into one plane; the link being of an oval form, and provided with a stay. As there are emergencies in which the cable must be severed, this is accomplished in those of iron by means of a bolt and sheckle (shackle), at every fathom or two fathoms; so that by striking out this bolt or pin, this cable is parted with more ease than a hempen one can be cut.
CACAO, BUTTER OF. See [Cocoa], and [Oils, Unctuous].