ON THE MECHANICAL PROPERTIES OF METALS. 



109 



&c. is only arrived at after the metal has undergone twelve successive melt- 

 ings. It is probable that other metals and their alloys may follow the same 

 law, but that is a question that has yet to be solved, and that jirobably by a 

 series of experiments which would require a considerable amount of time and 

 labour to accomplish. 



Having effected the experiments on the resistance of these metals to a 

 transverse strain, I next availed myself of a large wrought-iron lever and a 

 strong cast-iron frame, mounted for other researches, to ascertain their relative 

 powers of resistance to compression. This powerful apparatus had a lever 

 17 feet long, 12 inches deep, and 2| to nearly 3 inches thick, and tapered to 

 about 5 inches deep at the extreme end, where the weights were suspended. 

 This will, however, be better understood by the foregoing figure, which ex- 

 hibits the iron frame, lever, scale, weights, &c. by which the experiments 

 were effected, and the results in the following Tables obtained. A is the 

 lever, B the cast-iron frame, and C the shelf with a solid column below, 

 over which the specimen to be crushed was placed between two perfectly 

 flat steel discs at a. The column D was inserted under the shoulder of the 

 lever resting upon the specimen and upper disc, and retained in its vertical 

 position by the guide-plate E ; the metal cubes were crushed by adding 

 weights of 56 and 28 lbs. at a time to the scale F. 



In this way the whole of the specimens were crushed ; and in order to pre- 

 vent the weight falling so as to injure the fractured parts, a stop was placed 

 under the lever at G to receive the fall of the lever and scale when fracture 

 ensued. 



On the Resistance of Cast-iron, derived from repeated Meltings, to the Force 

 of Compression. 



The extraordinary results obtained from the foregoing experiments on a 

 transverse strain, induced a further extension of them to that of compression, 

 or the resisting powers of the metals in their different stages of successive 

 meltings to a force tending to crush them. This was a work of some diffi- 

 culty, as we found by repeated trials that our apparatus was not sufficient 

 to crush 1 inch cubes, and particularly those of the higher meltings, which 

 required a force of upwards of 90 tons to the square inch to produce frac- 

 ture. Finding the power of the lever inadequate for this purpose, the cubes 

 were reduced from 1 inch to a base of three-fourths and five-eighths of an 

 inch; and having fixed the fulcrum of the lever equivalent to a force of 

 100 tons, the experiments were proceeded with consecutively in the order of 

 the meltings, as exhibited in the following Tables. 



Experiments to determine the comparative resisting powers of cast-iron cubes 

 derived from repeated meltings, to a force tending to crush them. 



Experiment I. — First Melting. 



