466 



METALLURGY. 



temperature employed in the conversion of the 

 malleable metal from its primitive form. When 

 we speak of structural steel, in contradistinction to 

 structural wrought iron, it should be understood 

 that the distinction lies in the mode of manufacture 

 (the former being prepared by fusion and the latter 

 by agglutination), and not necessarily in any essen- 

 tial difference in the composition of the metals. Dur- 

 ing the puddling process iron will not agglutinate 

 until the extraneous elements, principally carbon 

 and silicon, are almost entirely removed. Broadly 

 speaking, there is little variation in the physical 

 properties of iron properly worked. Its tensile 

 strength will not vary much from 50,000 pounds per 

 square inch of sectional area, and it remains nearly 

 uniform in hardness. On the contrary, by the 

 fusion process the finished metal may retain carbon 

 varying from nothing to 1-J per cent, or more ; it 

 may also contain, by choice or necessity, a consid- 

 erable quantity of manganese or silicon. Its tensile 

 strength may vary from 50,000 pounds to 150,000 

 pounds per square inch of section. It may be 

 softer than ordinary iron produced by agglutina- 

 tion or it may be the hardest tool steel; yet in all 

 its gradations, which insensibly merge together, it 

 possesses certain characteristics which are common 

 to all, so that we can not discern any dividing 

 line and assert that all metal on one side is steel, 

 and all on the other side is not steel. While it 

 may be true to a limited extent that the composi- 

 tion of steel is not an index of its physical proper- 

 ties, it is the tendency of the modern open-hearth 

 practice to produce metal of more uniform compo- 

 sition than formerly, varying the carbon content 

 according to the tensile strength or hardness de- 

 sired, with the result that the physical properties are 

 also more uniform than before. It is probable that 

 each element modifies to some extent the influence 

 of others, so that the interplay of the whole, due to 

 varying proportions, becomes a matter of great 

 complexity. The great impetus given to the pro- 

 duction of structural steel in recent years is due, 

 not to its superiority over good wrought iron, but 

 to the fact that it can be produced more cheaply. 

 Besides the source of weakness from the formation 

 of cavities in the interior of the mass, another 

 liability arises from the tendency of the extraneous 

 materials in the metal to separate from the mass 

 just before solidification, and accumulate, generally 

 near the middle, making there a hard, possibly a 

 worthless, part of the metal. If the ingot is forged 

 into a shaft, the segregated mass will probably be 

 drawn out to a slender core along the central axis. 

 There is, therefore, a practical advantage in boring 

 a hole through the center of important shafts, as it 

 probably removes a segregated core. Welding of 

 structural steel has been abandoned for all work of 

 vital importance. Structural steel for buildings, 

 bridges, etc., of excellent quality, will analyze as 

 follows : Carbon, O'lO to 0'25 percent. ; manganese, 

 below 0'60 per cent. : silicon, below O'lO per cent. ; 

 phosphorus and sulphur, each below O'OG per cent. 

 Steel, whether of high or low tensile strength, has a 

 uniform modulus of elasticity that is, all grades 

 extend or compress or deflect alike under similar 

 loads below the elastic limit of the material. 

 Therefore high tensile strength is not always avail- 

 able, as the engineer hits to consider stiffness and 

 rigidity as prime factors in the satisfactory use and 

 endurance of structures. The production and 

 manipulation of steel require a higher degree of 

 skill and intelligence to obtain satisfactory results 

 than were formerly devoted to wrought iron. 



A method of making chains of steel, iron, and 

 other metals without welding has been invented by 

 Mr. W. Walkington, of Leeds, England. The weld- 

 less link is made by slitting each end of the bar, 



and then so manipulating the holes that they are 

 large enough to allow the bar forming the next 

 link to pass through them. It is contended that 

 the weldless chain can be produced at less than 

 half the cost of the ordinary welded article. Prof. 

 Goodman, of Yorkshire College, has subjected a 

 sample of the new steel chain to a test, along with 

 a straight bar of the steel of which the links were 

 made, and specimens of chains of the same size 

 made from the best Yorkshire and best Stafford- 

 shire iron. The straight steel bar broke at 6'72 

 tons, but the weldless steel chain only gave way with 

 a pressure of 10'21 tons. A welded chain of York- 

 shire iron said to be the best procurable in the 

 market broke with a pressure of 10'03 tons. Sub- 

 sequently, experiments made were even more favor- 

 able to the new chain, a specimen of which stood 

 10'20 tons, while a Yorkshire iron chain broke at 

 9'70 tons, and one made of best Staffordshire iron at 

 9'57 tons. 



Recalling the observations of Prof. Ramsay on 

 the reduction of the vapor pressure of mercury by 

 dissolved metals, from which the conclusion was 

 drawn that at the boiling point of mercury the 

 molecular weight of the metal in solution is in gen- 

 eral equal to its atomic weight, M. Guntz puts for- 

 ward the idea that in the case of metals extracted 

 from their amalgams at a low temperature the resi- 

 due consists, for the most part, of the element in 

 its atomic state. This, and not merely the fine 

 state of division, he regards as the explanation of 

 the energetic properties exhibited by such metallic 

 solutions. In support of this view thermo-chemical 

 data are given for ordinary fused manganese and 

 manganese from its amalgam, the heats of combi- 

 nation with oxygen showing that the conversion of 

 the latter into the former is accompanied with the 

 evolution of heat. Chromium and molybdenum 

 also, which after being fused are unchanged in air, 

 are pyrophoric when extracted from their amalgams 

 at low temperatures. M. Guntz purposes to study 

 the heats of polymerization of several metals, more 

 especially of iron. 



Investigations have been carried on by Prof. A. 

 J. Fleming and' Prof. Dewar to determine, by the 

 use of the cold of liquid air, the effect of tempera- 

 tures more than 200 below the freezing point of 

 water upon the principal magnetic and electric 

 properties of metals. It is found that the conduc- 

 tivity of pure iron wire, which at ordinary tempera- 

 tures is only about one sixth that of copper wire of 

 the same size, is increased nine or ten times under 

 the influence of the cold of liquid air. But while 

 pure metals thus have their conductivity immensely 

 increased by intense cold, alloys, such as brass or 

 German silver, experience under the same circum- 

 stances a comparatively small increase in conduct- 

 ing power, or not more than 10 per cent. By care- 

 fully examining the variations in the electrical 

 resistance of a large number of chemically pure 

 metals, the authors have established that every pure 

 metal would probably have no electrical resistance 

 at the zero of absolute temperature, or, in other 

 words, would become a perfect conductor of elec- 

 tricity. In this condition the passage of an electric 

 current would generate no heat in it. Another con- 

 sequence would be that a pure metal at the absolute 

 zero would form an absolutely opaque screen to 

 electro-magnetic radiation. The experiments fur- 

 nish an additional proof that the process by which 

 an electric current is conveyed from place to place 

 is primarily dependent upon actions going on out- 

 side that which we usually speak of as the conduct- 

 or. At the absolute zero any electrical power, 

 however large, can be transmitted along metallic 

 wires, however small, without loss of energy, the 

 wire becoming then a mere boundary and the en- 



