It has already been stated that the strength and elasticity of wrought iron depend not only upon its quality, but upon the treatment to which it has been subjected in working, and upon other surrounding circumstances.

The following Table shows concisely the effect produced by different modes of working, by changes of temperature, etc.

The conclusions given are founded upon a large number of experiments by Mr. Kirkaldy and others. Those by Mr. Kirkaldy are clearly classified in Mr. Kinnear Clarke's Hides and Tables for Mechanical Engineers.

Tensile Strength. Ductility.

Reducing diameter by rolling, forging, or hammering..

Increased .

Reduced.

Turning or removing skin..

No alteration .

No alteration.

Annealing .....

Reduced .

Increased.

Welding.....

Reduced from between

Reduced.

4.1 and 43.8 per cent

Stress suddenly applied ...

Reduced 18.5 per cent

Reduced in nearly all cases.

Hardening in water or oil..

Increased .

Reduced.

Cold rolling - plates..

Doubled .

Destroyed.

bars .

Increased 50 per cent

Reduced 60 per cent.

Galvanising .....

No difference.

Effect of frost 23° F...

Reduced 2.3 per cent

Reduced 8 per cent.

Effect of frost, stress suddenly applied

Reduced 3.6 per cent

Reduced between 0 and 30 per cent.

Effect Of Temperature

Sir William Fairbairn found that the strength of wrought iron was practically the same at all temperatures between 0. and 400° Fahr.6

1 Kennedy, Iron, 11th May 1883. 2 Institute Mechanical Engineers, 4th August 1885. 3 Architect, 18th February 1882. 4 Stoney. 5 Downing.

6 Useful Information for Engineers, Series ii.