pressed air, which divides it into innumerable small shot or spher ules, forming a spray of spark-like objects. The threads are spun

out immediately upon the detachment of the slag particles from the main body of the stream, their length and fineness being dependent upon the fluidity and composition of the material under treatment. When the slag is of the proper consistency, the spherules are small at the outset, and are to some extent absorbed into the fibre; but in no case will they disappear entirely, so that a great portion of the wool contains them, and is only separated from them by riddling. That portion of the mineral wool which is carried away from the shot by air-currents is very light (fourteen pounds per cubic foot), and forms an extra grade; while the balance has a working-weight of twenty-four pounds per cubic foot, and is called ordinary mineral wool.

The extra grade of mineral wool contains about ninety-three per cent of its volume of air, and the ordinary mineral wool eightyeight per cent.

This air circulates with such difficulty that moderate thicknesses of the stuff prevent the passage of heat, and perfect insulation may be obtained at small cost.

Mineral wool is used in buildings to fill between the studs and joists, to keep out the cold in winter and heat in summer, and effectually closing up all passages in which vermin and insects generally make their homes, and fires are communicated without a possibility of arrest.

It is peculiarly adapted for deafening floors; because it is used dry. and is inelastic, and therefore does not transmit the vibrations necessary to the communication of sound.

Mineral wool is also used largely for packing around steam and hot-water pipes to prevent loss of heat before reaching the radi

ators.

Ordinary mineral wool weighs about 24 pounds per cubic foot, and is put up in bags containing from 60 to 90 pounds in each bag. It costs at the works, in Stanhope, N.J., 1 cent per pound, and at store in New-York City, 14 cents per pound.

Extra mineral wool weighs about 14 pounds per cubic foot, and is put up in bags containing from 25 to 45 pounds in each bag. It costs, at the works, 3 cents per pound, and at the store, New-York City, 3 cents per pound.

RELATIVE HARDNESS OF WOODS.

Taking shell-bark hickory as the highest standard of our foresttrees, and calling that 100, other trees will compare with it for hardness as follows:

[From the "North-western Lumberman," 1883.)

The Boston law for the survey of black walnut and cherry, ash, oak, poplar, and butternut, requires that the woods be divided into three grades, number one, number two, and culls.

Number one includes all boards, plank, or joist that are free from rot and shakes, and nearly free from knots, sap, and bad taper: the knots must be small and sound, and so few that they would not cause waste for the best kind of work. A split in a board or plank, if parallel with the edge of a piece, is classed number one. Number two includes all other descriptions, except when onethird is worthless; when a board, plank, or joist contains sap, knots, splits, or any other imperfections combined, making less than one-third of a piece unfit for good work, and only fit for ordinary purposes, it is number two; when one-third is worthless, it is a cull, or refuse. Refuse or cull hard wood includes all boards, plank, or joist that are manufactured badly, by being sawed in diamond shape, smaller in one part than in another, split at both ends, or with splits not parallel, large and bad knots, worm-holes, sap, rot, shakes, or any imperfections which would cause a piece of lumber to be one-third worthless or waste.

All hard woods are measured from six inches up; and all lumber sawed thin is inspected the same as if of proper thickness, but is ssed as thin, and sold at the price of thin lumber.

There is no such thickness as 3-inch lumber : the regular sizes are, 1, 1, 1, 2, 2, 3, 4 inch, and up, on even inches. The regular lengths are 12, 14, and 16 feet; shorter than 12 does not command full market price.

HORSE-POWER.

A horse can travel 400 yards at a walk in 4 minutes, at a trot in 2 minutes, and at a galop in 1 minute; he occupies in a stall from 3 to 4 feet front, and at a picket 3 feet by 9; and his average weight equals 1000 pounds.

A horse carrying 225 pounds can travel 25 miles in a day of S hours.

A draught-horse can draw 1600 pounds 23 miles a day, weight of carriage included.

In a horse-mill a horse moves at the rate of 3 feet in a second. The diameter of the track should not be less than 25 feet.

A horse-power, in machinery, is estimated at 33,000 pounds, raised 1 foot in a minute; but as a horse can exert that force but six hours a day, one machinery horse-power is equivalent to that of 4 horses.

The strength of a horse is equivalent to that of five men.

The daily allowance of water for a horse should be four gallons,

Reduction for Round Cores and Core Prints.

RULE. - Multiply the square of the diameter by the length of the core in inches, and the product multiplied by 0.017 is the weight of the pine core to be deducted from the weight of the pattern.

RULES FOR CALCULATING THE SPEED OF DRUMS AND PULLEYS.

The diameter of the driver being given, to find its number of revolutions.

RULE. Multiply the diameter of the driver by the number of its revolutions, and divide the product by the diameter of the driven the quotient will be the number of revolutions of the driven.

The diameter and revolutions of the driver being given, to find the diameter of the driven that shall make any given number of revolutions in the same time.

RULE. Multiply the diameter of the driver by its number of revolutions, and divide the product by the number of revolutions of the driven: the quotient will be its diameter.

To ascertain the size of the driver.

RULE. - Multiply the diameter of the driven by the number of revolutions you wish it to make, and divide the product by the revolutions of the driver: the quotient will be the diameter of the driver.

N. B. In ordering pulleys, be careful to give the exact size of the shaft on which they are to go; also state how you wish them finished on the face, flat face for shifting belt, rounding for non-shifting belt.

WEIGHT OF GRINDSTONES.

RULE. -Square the diameter (in inches), multiply by thickness (in inches), then multiply by decimal 0.06363.

EXAMPLE. Find the weight of a stone 4 feet 6 inches diameter and 7 inches thick.

4 feet 6 inches = 54 inches; square of 54 = 2916; multiplied by 7 = 20412; multiplied by 0.06363 = Ans. 1298.815 pounds, which is weight of stone.

MISCELLANEOUS MEMORANDA.

Weight of Men and Women. The average weight of twenty thousand men and women weighed at Boston, 1864, was, men, 1411⁄2 pounds; women, 1241⁄2 pounds.

Smallest Convenient Size of slab for a 14-inch wash-bowl, 21 by 24 inches. Height of slab from floor, 2 feet 6 inches. Very small (12-inch) corner wash-bowl; slab, 1 foot 11 inches each side.

Urinals should be 2 feet 2 inches between partitions; partitions 6 feet high.

Space occupied by Water-Closets, 2 feet 6 inches wide, 2 feet deep.

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Dimensions of Double Bed. -6 feet 6 inches by 4 feet 6 inches. Dimensions of Single Beds (in dormitories). - 2 feet 8 inches by 6 feet 6 inches.

Dimensions of a Bureau.-3 feet 2 inches wide, 1 foot 6 inches deep, and upwards.

Dimensions of a Washstand (common chamber-sets). - 2 feet 4 inches wide, 1 foot 6 inches deep.

Dimensions of a Barrel. - Diameter of head, 17 inches; bung, 19 inches; length, 28 inches; volume, 7680 cubic inches.

Dimensions of Billiard-Tables (Collender). -4 feet by 8 feet, 4 feet 2 inches by 9 feet, and 5 feet by 10 feet. Size of room required, 13 feet by 17 feet, 14 feet by 18 feet, and 15 feet by 20 feet respectively.

Horse-Stalls. - Width, 3 feet 10 inches to 4 feet, or else 5 feet or over in width, 9 feet long. Width should never be between 4 and 5 feet, as in such cases the horse is liable to cast himself. Dimensions of Drawings for Patents (United States). — 10 × 15 inches, with border line one inch inside all around.

Pitch of Tin, Copper, or Tar-and-Gravel Roof. - Five-eighths of an inch to the foot, and upwards.

A fall of one-tenth of an inch in a mile will produce a current in rivers.

Melted snow produces from one-fourth to one-eighth of its bulk in water.

At the depth of forty-five feet, the temperature of the earth is uniform throughout the year.

A spermaceti candle 0.85 of an inch in diameter consumes an inch in length in an hour.

Velocity of sound in water, 4708 feet per second.

Avenues of City of New York run 28° 50′ 30′′ east of north.

Average Height of Hand Rail to Stairs in Dwellings.

7 inches from top of step on line with riser.

- 2 feet