MECHANICS AND USEFUL ARTS. 37 



good charcoal irons and with steel. The greatest cohesion is ac- 

 companied by a fine, close-grained, uniform appearance of texture, 

 which, under a magnifying glass, exhibits fibre. The color is a sil- 

 very lustre, free from dark specks. The finer and more close-grained 

 the texture, the nearer the iron approaches to steel. Those who are 

 familiar with good Swedish or Norway irons will support these 

 statements. These facts alone should be sufficient to disprove the 

 erroneous notion that good iron and steel, which should always be 

 granular, will become so only by vibration, and will thereby lose 

 their strength. But it is important to keep in mind the distinction 

 between a fine, uniform, granular fracture, and a coarse crystalline 

 fracture. Where coarse crystallization appears, there is a want of 

 contact and compactness, consequently of cohesion and strength 

 generally. 



Wire cables, car-axles, piston-rods, connecting rods, and all such 

 pieces of machinery, which are exposed to great tension as well as 

 torsion and vibration, should be manufactured of iron which not only 

 possesses great cohesion, but also a high degree of hardness and elas- 

 ticity. The best car-axles now in use are those made of soft steel 

 by Krupf, in Germany. This steel is manufactured from the spathic 

 ore, or natural steel ore, of the celebrated mines at Muessen in Siegen, 

 Prussia. A correct report on these axles was given to me by one 

 of the Prussian commissioners of railways, in whose district Krupf s 

 works are located. They are safe in cold weather, and seldom known 

 to break. This proves that soft steel with more of a granular texture 

 than fibre possesses a much greater elasticity and strength than the 

 best fibrous iron ; and it also furnishes another strong proof against 

 the granulation theory, so much credited in this country. 



It may be objected that steel is a different metal from iron. But 

 all irons and steels are only so many different alloys of the same 

 metal. There is no essential difference between the two. What 

 constitutes the true chemical and physical difference between the two 

 varieties is not so clear. 



The capacity of irons to resist vibration and tension differs much 

 in different qualities, and still greater is this difference when the irons 

 are exposed to a very cold temperature. The tubular bridge at Mont- 

 real will not last as long as one in Great Britain of the same dimen- 

 sions, material, and workmanship, and rendering the same service ; 

 and still less than the tubes over the Nile, in Egypt. One hard winter 

 in Canada will be as trying to the structure as ten years are in Great 

 Britain. 



In order to examine the fitness of various qualities of iron for the 

 manufacture of wire rope, I undertook, during the hard winter of 1856, 

 at my establishment at Trenton, a series of experiments, when the 

 thermometer was five to ten degrees below zero. The samples for 

 testing, about one foot long, were reduced in the centre to exactly 

 three-quarters of an inch square, and their ends, left larger, were 

 welded to heavy eyes, making in all a bar of three feet long. Thus 

 prepared, they were thrown outside of the mill, covered with snow and 

 ice, and left exposed for several days and nights. Early in the morn- 

 ing, before the air grew warmer, a sample, inclosed in ice, would 

 be put in the testing machine, and at once subjected to a strain of 



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