CABLES AND ANCHORS.

TABLE showing the Size of Cables and Anchors proportioned to the
Tonnage of Vessels.

The proof in the U. S. Naval Service is about 124 per cent. less than the above.

The utmost strength of a good hemp rope is 6400 lbs. to the square inch; in prac-
tice it should not be subjected to more than half this strain. It stretches from to
4, and its diameter is diminished from to before breaking.

A difference in the quality of hemp may produce a difference of in the strength
of ropes of the same size.

The strength of Manilla is about that of hemp.

White ropes are one third more durable.

CABLES.

TABLE showing what Weight a good Hemp Cable will bear with

Safety.

To ascertain the Strength of Cables.

Multiply the square of the circumference in inches by 120, and the product is the weight the cable will bear in pounds, with safety.

To ascertain the Weight of Manilla Ropes and Hawsers.

Multiply the square of the circumference in inches by .03, and the product is the weight in pounds of a foot in length.

This is but an approximation, and yet it is sufficiently correct for many purposes.

TABLE showing what Weight a Hemp Rope will bear with Safety.

To ascertain the Strength of Ropes.

Multiply the square of the circumference in inches by 200, and it gives the weight the rope will bear in pounds, with safety.

To ascertain the Weight of Cable-laid Ropes.

Multiply the square of the circumference in inches by .036, and the product is the weight in pounds of a foot in length.

To ascertain the Weight of Tarred Ropes and Cables.

Multiply the square of the circumference by 2.13, and divide by 9; the product is the weight of a fathom in pounds.

Or, multiply the square of the circumference by .04, and the product is the weight of a foot.

For the ultimate strength, divide the square of the circumference in inches by 5; the product is the weight in tons.

A

square inch of hemp fibres will support a weight of 9200 lbs.

BLOWING ENGINES.

THE object of a blast is to supply oxygen to furnaces.

The quantity of oxygen in the same bulk of air is different at different temperatures. Thus, dry air at 85° contains 10 per cent. less oxygen than when at the temperature of 32o; when saturated with vapour, it contains 12 per cent. less.

Hence, if an average supply of 1500 cubic feet per minute is required in winter, 1650 feet will be required in summer.

The pressure ordinarily required for smelting purposes is equal to a column of mercury from 3 to 7 inches.

The capacity of the Reservoir should exceed that of the cylinder or cylinders, and the area of the pipes leading to it should be of the area of the cylinder.

The quantity of air at atmospheric density delivered into the reservoir, in consequence of escapes through the valves, and the partial vacuum necessary to produce a current, will be about less than the capacity of the cylinder.

To find the Power when the Cylinder is Double Acting. Let P represent pressure in lbs. per square inch,

66

v

a

1.25

the velocity of the piston in feet per minute,
the area of the cylinder in inches,

the friction necessary to work the machinery. Then Pva 1.25= the power in lbs. raised 1 foot high per minute,

Pva 1.25

2

When Single Acting.

= the power in lbs. raised 1 foot high per minute.

Air expands nearly 21⁄2 times its bulk while in the fire of an ordinary furnace.

Dimensions of a Furnace, Engines, &c.

Furnace. At Lonakoning (Md.). Diameter at the boshes 14 feet, which fall in, 6.33 inches in every foot rise.

Engine. Diameter of cylinder 18 inches, length of stroke 8 feet.

Averaging 12 revolutions per minute, with a pressure of 50 lbs. per square inch. Boilers. Five: each 24 feet in length, and 36 inches in diameter.

Blast Cylinders. 5 feet diameter, and 8 feet stroke.

At a pressure of from 2 to 24 lbs. per square inch, the quantity of blast is 3770 cubic feet per minute, requiring a power of about 50 horses to supply it.

180 tons air is required to make 10 tons pig iron, and burn the coke from 50 tons coal. The ore yielding about 33 per cent. of iron.

Steam Boilers. Two cylinders, 12 inches in diameter and 12 inches stroke, aided by exhausting into a condenser, and with steam of 30 lbs. pressure per square inch, will make 50 revolutions per minute, and drive 4 blowers, each 54 inches in diameter, and 30 inches wide, 300 revolutions in a minute, furnishing the necessary blast for burning anthracite coal on a grate surface of 108 square feet; supplying 4400 cubic feet steam per minute, at a pressure of 30 lbs. per square inch.

35 cubic feet of steam used in the cylinder of a blowing engine will drive blowers 4 feet in diameter by 26 inches face, and furnish the necessary blast to an anthracite fire, for generating 1150 cubic feet steam, the time 1 minute, an pressure per square inch 35 lbs.

MISCELLANEOUS NOTES.

ON MATERIALS, ETC.

Wood is from 7 to 20 times stronger transversely than longitudinally.

In Buffon's experiments, b, d, and I being the breadth, depth, and length of a piece of oak in inches, the weight that broke it in pounds

was bd2 (54.2510).

The hardness of metals is as follows: Iron, Platina, Copper, Silver, Gold, Tin, Lead.

A piece spliced on to strengthen a beam should be on its convex side.

Springs are weakened by use, but recover their strength if laid by.

A pipe of cast iron 15 inches in diameter and .75 inches thick will sustain a head of water of 600 feet. One of oak, 2 inches thick, and of the same diameter, will sustain a head of 180 feet.

When the cohesion is the same, the thickness varies as the height X the diameter.

When one beam is let in, at an inclination to the depth of another, so as to bear in the direction of the fibres of the beam that is cut the depth of the cut at right angles to the fibres should not be more than of the length of the piece, the fibres of which, by their cohesion, resist the pressure.

Metals have five degrees of lustre-splendent, shining, glistening, glimmering, and dull.

THE Vernier Scale is 11, divided into 10 equal parts; so that it divides a scale of 10ths into 100ths when the lines meet even in the two scales.

A luminous point, to produce a visual circle, must have a velocity of 10 feet in a second, the diameter not exceeding 15 inches.

Tides. The difference in time between high water averages about 49 minutes each day.

In Sandy soil, the greatest force of a pile-driver will not drive a pile over 15 feet. A fall of of an inch in a mile will produce a current in rivers. Melted snow produces about of its bulk of water.

All solid bodies become luminous at 800 degrees of heat.

At the depth of 45 feet, the temperature of the earth is uniform throughout the year.

A Spermaceti candle .85 of an inch in diameter consumes an inch in length in 1 hour.

Silica is the base of the mineral world, and Carbon of the organized.

Sound passes in water at a velocity of 4708 feet per second.