OF ENGINE BOILERS.

How many superficial feet are contained in a boiler 23 feet in length and 5 in width?

Set 1 upon B to 23 upon A; and against 5-5 upon B is 126-5 square feet upon A.

If 5 square feet of boiler surface be sufficient for each horse-power, how many horses' power of engine is the boiler equal to ?

Set 5 upon B to 126-5 upon A; and against 1 upon B is 25.5 upon A.

STRENGTH OF MATERIALS.

MATERIALS of construction are liable to four different kinds of strain; viz., stretching, crushing, transverse action, and torsion or twisting: the first of which depends upon the body's tenacity alone; the second, on its resistance to compression; the third, on its tenacity and compression combined; and the fourth, on that property by which it opposes any acting force tending to change from a straight line, to that of a spiral direction, the fibres of which the body is composed.

In bodies, the power of tenacity and resistance to compression, in the direction of their length, is as the cross section of their area multiplied by the results of experiments on similar bodies, as exhibited in the following table.

Table showing the Tenacities, Resistances to Compres sion, and other Properties of the common Materials of Construction.

Note. It must be understood and also borne in mind that,

in estimating the amount of tensile strain to which a body is subjected, the weight of the body itself must also be taken into account; for according to its position so may it approximate to its whole weight, in tending to produce extension within itself; as in the almost constant application of ropes and chains to great depths, considerable heights, &c.

Alloys that are of greater Tenacity than the Sum of their Constituents, as determined by the Experiments of Muschenbroek.

Swedish copper 6 pts., Malacca tin 1; tenacity per sq. inch 64,000 lbs.
Chili copper 6 parts, Malacca tin 1;
Japan copper 5 parts, Banca tin 1;
Anglesea copper 6 parts, Cornish tin 1;
Common block-tin 4, lead 1, zinc 1;
Malacca tin 4, regulus of antimony 1;
Block tin 3, lead 1;

Block tin 8, zinc 1;

Lead 1, zinc 1;

66

60,000" 57,000 $

41,000 "

66

13,000"

66

12,000"

10,200 "

10,000 ❝

4,500 "

The strength of a square or rectangular beam to resist lateral pressure, acting in a perpendicular direction to its length, is as the breadth and square of the depth,. and inversely as the length; thus, a beam twice the breadth of another, all other circumstances being alike, equal twice the strength of the other; or twice the depth, equal four times the strength, and twice the length, equal only half the strength, &c., according to the rule.

Table of Data, containing the Results of Experiments on the Elasticity and Strength of various Species of Timber, by Mr. Barlow.

To find the dimensions of a beam capable of sustaining a given weight, with a given degree of deflection, when supported at both ends.

Rule. — Multiply the weight to be supported in lbs. by the cube of the length in feet; divide the product by 32 times the tabular value of E, multiplied into the given deflection in inches; and the quotient is the breadth multiplied by the cube of the depth in inches.

Note 1.- When the beam is intended to be square, then the fourth root of the quotient is the breadth and depth required. Note 2.- -If the beam is to be cylindrical, multiply the quotient by 1.7, and the fourth root of the product is the di

ameter.

Ex. The distance between the supports of a beam of Riga fir is 16 feet, and the weight it must be capable of sustaining in the middle of its length is 8000 lbs., with a deflection of not more than of an inch; what must be the depth of the beam, supposing the breadth 8 inches?

15175÷8= 3√ 1897 = 12.35 in., the depth.

To determine the absolute strength of a rectangular beam of timber, when supported at both ends, and loaded in the middle of its length, as beams in general ought to be calculated to, so that they may be rendered capable of withstanding all accidental cases of emergency.

Rule. - Multiply the tabular value of S by four times the depth of the beam in inches, and by the area of the cross section in inches; divide the product by the distance between the supports in inches, and the quotient will be the absolute strength of the beam in lbs. Note 1. If the beam be not laid horizontally, the distance between the supports, for calculation, must be the horizontal

distance

Note 2.

-

One fourth of the weight obtained by the rule, is the greatest weight that ought to be applied in practice as perBrent load.