Experiments on cast iron bars give a tensile strength of from 4,000 lbs. to 5,000 lbs per square inch of its section, as just sufficient to balance the elasticity of the metal, and as a bar of it is extended the 5500th part of its length for every ton of direct strain per square inch of its section, it is deduced that its elasticity is fully excited when it is extended less than the 3000th part of its length, and the extension of it at its limit of elasticiy is estimated at the 1200th part of its length.

The mean tensile strength, then, of cast iron being from 16.000 to 20,000 lbs., the value of it, when subjected to a tensile strain, may be safely estimated at from ¼ to 1/3 of this, or of its breaking strain.

A bar of cast iron will contract or expand .000006173. or the 162000th of its length for each degree of heat; and assuming the treme range of the temperature in this country 140° ( - 20° + 1200), it will contract or expand with this change .0008642, or the 1157th part of its length. It shrinks in cooling from .0104 to .0118 of its length.

It follows, then, that as 2240 lbs. will extend a bar the 5500th part of its length, the contraction or extension for the 1157th part will be equivalent to a force of 10,648 lbs. (4¾ tons) per square inch of section.

Cast iron (Greenwood) at three successive meltings gave tenaci-UM of 21,300, 30,100, and 33,700 lbs.

Cast iron at 2.5 tons per square inch will extend the same as wrought iron at 5.6 tons.

The mean tensile strength of four kinds of English cast iron, as determined by the Commissioners on the Application of Iron to Railway Structures, was 15,711 lbs. per square inch (7.014 tons); and the mean ultimate extension was, for lengths of 10 feet, .1997 inch, being the 600th part of its length; and this weight would compress a bar the 775th part of its length.

Tensile strength of the strongest piece of cast iron ever tested - 45,970 lbs. This was a mixture of grades 1, 2, and 3 of Greenwood iron, and at the 3d fusion.