MECHANICS AND USEFUL ARTS. 43 



and the size of the grains diminished toward the extremities. In the 

 fifth, an axle submitted to 23,328,000 torsions, during seven hundred 

 and twenty hours, was completely changed in its texture ; the frac- 

 ture in the middle was crystalline, but not very scaly. In the sixth, 

 after ten months, during which the axle was submitted to 78,732,000 

 torsions and shocks, fracture produced by a hydraulic press showed 

 clearly an absolute transformation of the structure of the iron ; the 

 surface of rupture was scaly, like pewter. In the seventh and final 

 case, an axle submitted to 128,304,000 torsions presented a surface 

 of rupture like that in the preceding experiment ; the crystals were 

 found to be perfectly well defined, the iron having lost every appear- 

 ance of wrought iron. 



PROPERTIES OF A MIXTURE OF CAST-IRON AND NICKEL. 



Meteoric iron, as well known, is the most ductile of all varieties of 

 iron, and it is recorded by travellers that the Esquimaux have instru- 

 ments made from it so ductile that they may be made to bend round 

 the arm. All meteoric iron contains a small percentage of metallic 

 nickel, and it has been suggested by chemists that by mixing iron and 

 nickel artificially, an alloy of iron as strong and ductile as meteoric iron 

 would be obtained. With a view of testing this theory, and with a 

 hope of obtaining a metal of great tenacity, suitable for the casting of 

 cannon and heavy ordnance, Mr. Fairbairn, the celebrated English 

 engineer, has recently instituted a series of very carefully conducted 

 experiments of mixing a certain proportion of nickel with cast iron. 

 The result, however, has failed entirely to realize expectation, inas- 

 much as the ingots prepared were found to have less than one-half the 

 power to resist impact that similar ingots of pure iron possessed. 



"It is uncertain what might have been the results had the castings 

 produced been treated as cast steel, and hammered out until they were 

 rendered malleable and magnetic. This process was not, however, 

 attempted, as, judging from the appearance of the fracture, they were 

 more likely to crumble under the hammer than attain malleability." 



In a report on the above subject to the Manchester Philosophical 

 Society, Mr. Fairbairn says in conclusion, " During the last two years, 

 innumerable experiments have been made to produce a metal of in- 

 creased tenacity suitable for the construction of heavy ordnance ; but 

 the ultimate result appears to be, that there is no metal so well calculated 

 to resist the explosion of gunpowder as a perfectly homogeneous mass 

 of the best and purest cast iron, freed from sulphur and phosphorus." 



COMPARATIVE STRENGTH OF COLD-ROLLED AND HOT- 

 ROLLED IRON. 



The following is the result of a series of experiments recently insti- 

 tuted by Mr. Fairbairn, the celebrated English engineer, upon the 

 tensile strength of bars of wrought iron, rolled cold or hot : 



" The first experiment was on a bar of wrought iron, in the condition 

 in which it is received from the manufacturer (black). The diameter 

 of the piece experimented upon was 1.07 in. ; its area, 0.85873 square 

 inch. The laying on of a weight of 46,426 Ibs. produced an elongation 



