This formula is applicable, with little risk of error, to engines working with from 5 lbs. to 65 lbs. per square inch. TABLE

Of the Pressure on a square and circular Inch, respectively, excited by the elastic force of Steam at various degrees of Temperature, with the Height of the column of Mercury it will support.

1. PRESSURE ON A SQUARE INCH. 2. PRESSURE ON A CIRCULAR INCH.

To prevent Incrustation in boilers.-The introduc tion of potatoes and other vegetable substances will, in a great degree, prevent incrustation on the bottom and sides of a steam boiler, and animal substances, such as refuse skins, will accomplish it still more effectually.

Iron Cement for joining the Flanches of Iron Pipes, &c. Take of Sal Ammoniac, 2 ounces; Flowers of Sulphur, 1 ounce; clean cast-iron Borings or Filings, 16 ounces: mix them well in a mortar, and keep them dry. When required for use, take one part of this powder, and twenty parts of clean iron borings or filings, mix them thoroughly in a mortar, make the mixture into a stiff paste with a little water, and apply it between the joints, and screw them together. A little fine grindstone sand added, improves the cement. mixture of white paint with red lead, spread on canvas or woollen, and placed between the joints, is best adapted for joints that require to be often separated.

Α

For Copper, a cement is used, composed of powdered quick lime, mixed to a proper consistence with serum of blood, or white of egg-and used immediate. ly it is made.

THE MECHANICAL POWERS.

Power is compounded of the weight and expansive force of a moving body multiplied into its velocity.

The power of a body which weighs 40 lbs., and

moves with the velocity of 50 feet in a second, is the same as that of another body which weighs 80 lbs., and moves with the velocity of 25 feet in a second; for the products of the respective weights and velocities are the same.

40 multiplied by 50-200; and 80 by 25-2000

Power cannot be increased by mechanical means. Power is applied to mechanical purposes by the lever, wheel and axle, pulley, inclined plane, wedge, and the screw, which are the simple elements of all machines.

The whole theory of these elements consists simply, in causing the weight which is to be raised, to pass through a greater or a less space than the power which raises it; for, as power is compounded of the weight or mass of a moving body multiplied into its velocity, a weight passing through a certain space may be made to raise, through a less space, a weight heavier than itself.

Power is gained at the expense of space, by the lever, the wheel and axle, the pulley, the inclined plane, the wedge, and the screw.

LEVER.

Case 1.-When the fulcrum of the lever is between the power and the weight.

RULE.-Divide the weight to be raised by the power to be applied; the quotient will give the difference

brio.

of leverage necessary to support the weight in equili Hence, a small addition either of leverage or weight will cause the power to preponderate.

EXAMPLE 1.-A ball weighing 3 tons, is to be raised by 4 men, who can exert a force of 12 cwt., required the proportionate length of lever?

In this example, the proportionate lengths of the lever to maintain the weight in equilibrio, are as 5 to 1. If, therefore, an additional pound be added to the power, the power side of the lever will preponderate, and the weight will be raised. But, although the ball is raised by a force of only one-fifth of its weight, no power is gained, for the weight passes through only one-fifth of the space. The products, therefore, arising from the multiplication of the respective weights and velocities are the same.

EXAMPLE 2.-A weight of 1 ton is to be raised with a lever 8 feet in length, by a man who can exert, for a short time, a force of rather more than 4 cwt.: required at what part of the lever the fulcrum must be placed?

20 cwt.

4 cwt.

5; that is, the weight is to the power as 5 [to 1: therefore,

= 1 foot and a third from the weight. 5 multiplied by 1

EXAMPLE 3.-A weight of 40 pounds is placed one foot from the fulcrum of a lever; required the power to raise the same when the length of the lever on the other side of the fulcrum is five feet?

Case 2.-When the fulcrum is at one extremity of the lever, and the power at the other.

RULE. As the distance between the power and the fulcrum is to the distance between the weight and the fulcrum, so is the effect to the power.

EXAMPLE 1.-Required the power necessary to raise 120 lbs., when the weight is placed six feet from the power, and two feet from the fulcrum?

As 8: 2 :: 120 : 30 lbs., Ans.

EXAMPLE 2.-A beam, 20 feet in length, and supported at both ends, bears a weight of two tons at the distance of eight feet from one end: required the weight on each support?

40 cwt. multiplied by 8 ft.

20 feet

16 cwt. on the support