STR

478

S T E

Table showing the Compression of a Cast-iron Bar , 10 feetlong, and 1 inch Square.

Tons.

Compressionper Ton.

Total Compres-sion.

Total permanent£et.

Inch.

Inch.

' Inch.

1

.020338

.020338

.000510

2

.021038

.042077

.002452

3

.021618

.064855

.004340

4

.021369

.085479

.006998

5

.021594

.107872

.009188

6

.021752

.130513

.011798

7

.021950

.153654

.015243

8

.022154

.177235

.018572

9

.022374

.201373

.024254

10

.022477

.224774

.028126

11

.022567

.248237

.032023

12

.022802

.273632

.037653

13

.023014

.299187

.043318

14

.023523

.329330

.052640

15

.023539

.353092

.060905

16

.024409

.390558

.080256

17

.024805

.421695

.086298

Table showing the Compression of Wrought and Cast-ironBars, 10 feet long, and 1 inch square nearly. The Experi-ments made by Mr. Hodgkinson.

Cast-iron Bar.

Area of Section 1.031 X 1.029.

Wrought-iron Bar.

Area of Section 1.025X 1.025.

Weight laid onthe Bar.

Decrease oflength by thatWeight.

Decrease oflength of theBar.

Weight produ-cing that De-crease.

lbs.

Inch.

Inch.

lbs.

5054

.054

.052

9578

7316

.078

.073

14058

11818

.126

.130

25258

14058

.157

.154

29738

20778

.173

.174

31978

21898

.210

.214

34218

Table showing the Average Breaking- Weight of Bars 1 inchsquare, and 3 feet long, as determined from a very extensiveseries of experiments by Mr. Robert Stephenson.

Iron.

Ultimate Deflection.

Breaking Weight.

Hot blast .

.789

826

Cold blast .

.784

855

Mixtures of various Irons

898

General Observations.

The tenacity of good Baltic fir is very remarkable ; soundrods of this material will bear an ultimate tensile strain of5 tons per square inch, the specific gravity of which beingfrom £ to £ of that of water, so that it will be about £ or £immersed when floating in that liquid; the weight may betaken generally at about 45 lbs. per cubic foot, or nearlyone-tenth that of wrought-iron, while the ultimate strengthamounts to one-fourth. Thus a tension-rod of wrought-ironwill be 2£ times as heavy as a tension-rod of Baltic fir of thesame strength, and of four times the sectional area.

Its elasticity is about one-fifteenth that of wrought-iron ;i. e. a bar one inch square is extended on -xj-yVini th itslength per ton of direct tensile strain.

The difficulty of connecting timber longitudinally) . ncomplete bar to the use of deal in cases of tensile stra 'j )a ’]liSgreater lengths than it is naturally produced ; the ‘ gimported vary from 40 to 60 and 70 feet in length,from 12 to 16 inches square. 0I) d

In practice, wrought-iron should not be strained hey ^10 tons per square inch, and deal 2£ tons per square * nAn ordinary round rod of wrought-iron, 1 inch in dia®bears tensilely 16 tons, and weighs 8 lbs per yard. t j,e

For a round rod of any diameter, the square 0 , ]t

diameter, taken in greater inches, is the breaking ,vin tons.

Half this quantity is the weight in lbs. per yard. r ,the breaking weight of a round bar 5 inches, or 20 q liainches in diameter, will be 20 X 20 or 400 tons, anactual weight will be half 400 or 200 lbs. per yard. j B(A rod will be perceptibly damaged by half this s twhich can never be safely exceeded, one-third being auin practice. _ t the

The strength of chain-cable is thus easily arrived a Y; c (istrength of a link being double that of the bar from

it is forged. the ir

It is usual technically to denominate chains vydiameter, thus a five-eighth chain is a chain madea bar £ inch in diameter. conve'

The following approximations will be found very t j )6nient in estimating the weight and strength of c ' iain ft ’ t l6ultimate tensile strength of the material being taken . ^tons per circular inch, or 20 tons per square inch oj s jgjt

1. The square of the diameter in eights, will be the °

of the chains in lbs. per fathom. , 2,

2. The square of the diameter in eights, divide ^j n g'will be the breaking weight in tons. Thus the bre , t }jeweight of a £ chain will be half 25 tons = 12£ tons, aactual weight will be 25 lbs. per fathom of 6 feet- ^ ( j)is

M.B .—A chain will be perceptibly damaged by ^jpgstrain, which can never be safely exceeded, one-tinsufficient in practice. . s j z e 13

The strength of ropes is very uncertain, t ‘ ie ’ r nC e i°generally denominated technically by their circum ve r j

inches; and the following approximations willcorrect for ordinary tarred hempen rope :— divide^ by

1. The square of the circumference in inches, wiH be10, will give the practical strength in tons, whi

about half their breaking-weight. . v 4, ' V1 ‘

2. The square of the circumference, divided ’y^ g us e-roughly give the weight in lbs. per fathom. l* lU t j, e uld'ful strength of a 5 inch rope will be ^ or 2.5 tons, ^ tar re“mate strength being 5 tons ; and the weight o

5-inch rope will be 5 s or 6£lbs. per fathom. , 9 cl iainA rope of 10 inches in circumference, an j q toD s >of ^ 3 ths diameter, will each bear practically a 0 { tb^taking half the breaking-weight, and the wei£former will be 25 lbs., and of the latter, 2fathom. , p e n

Transverse Strength of a Slab of Slate from »

Quarries. . , thick,

A slab of slate 2 feet 10 inches broad, 4 ,ncn g jjgtrib 1114 feet between the bearings, failed with 24£ tonsover 15 inches at the the centre of the span. sc ar< j 9

A slab of cast-iron of the same dimensions w ^

support five times as much, and would be abo oo*half times as heavy. This material forms a vafor bridges. -.- a e

Transverse Strength of Timber, ofTo avoid any anomalies in deducing the s * r fte us,beams of timber from experiments on small ba

ef