METALLURGY. 



481 



out fracture. Hadfield has given us manganese 

 steel that will not soften by annealing, while 

 duillaume has studied the properties of certain 

 nickel steels that will not expand by heat, and 

 others that contract when heated and expand 

 when cooled. Nickel, chromium, titanium, and 

 tungsten are freely alloyed with iron, and the 

 use of vanadium, uranium, molybdenum, and 

 even glucinum is suggested. Steel rails are made 

 which will remain in use seventeen years and 

 only lose 5 pounds per yard, though 50,500,000 

 tons of traffic pass over them. Huge ingots are 

 placed in soaking pits and forged direct by 120- 

 ton hammers or pressed into shape by 14,000-ton 

 presses. Steel castings for parts of ships are made 

 that weigh more than 35 tons. We electrically 

 rivet and electrically anneal hardened ship plates 

 that could not otherwise be drilled. Photo-mi- 

 crography enables us to study the pathology of 

 steel and to suggest remedial measures for its 

 treatment. Ewing and Rosenhain have recognized 

 quite recently by its aid that the plasticity of a 

 metal is due to " slip " along the cleavage planes 

 of crystals, and by its aid Osmond has shown 

 that the entire structure of certain alloys can be 

 changed by heating to so IOW T a temperature as 

 225 C. The range of properties possessed by 

 steel is wide, and by its use the efforts of a mul- 

 titude of workers have been, as it were, concen- 

 trated in a few great efforts which have exerted 

 vast influence on the progress of mankind. 



Much information has been obtained regarding 

 the structure of metals by microscopic examina- 

 tion. When a highly polished surface of metal 

 is lightly etched and examined under the micro- 

 scope it reveals a structure which shows that 

 the metal is made up in general of irregularly 

 shaped grains with well-defined bounding surfaces. 

 The exposed face of each grain has been found 

 to consist of a multitude of crystal facets, hav- 

 ing a definite orientation. Seen under oblique 

 illumination, these facets exhibit themselves re- 

 flecting the light in a uniform manner over each 

 single grain, but in very various manners over 

 different grains, and, by changing the angle of 

 incidence of the light, one or another grain is 

 made to flash out comparatively brightly over 

 its whole exposed surface, while others become 

 dark. The grains appear to be produced by crys- 

 tallization, proceeding, more or less simultaneous- 

 ly, from as many centers or nuclei as there are 

 grains, and the irregular, more or less polygonal 

 boundaries which are seen on a polished and 

 etched surface result from the meeting of these 

 crystal growths. In experiments by Prof. Ewing 

 and Walter Rosenhain to witness the behavior 

 of the crystalline grains when the metal is sub- 

 jected to strain a polished surface was watched 

 under the microscope while the metal was grad- 

 ually extended till it broke. When a piece of 

 iron or other metal exhibiting the usual granu- 

 lar structure was stretched beyond its elastic 

 limit sharp, black lines gradually appeared on 

 the faces of the crystalline grains ; of a few grains 

 only at first, but of more as the straining was 

 continued. On each grain they were more or 

 less straight and parallel, but their directions 

 were different on different grains. The appear- 

 ance of each grain is so like that of a crevassed 

 glacier that these dark lines might readily be 

 taken for cracks. They are, however, not cracks, 

 but slips along planes of cleavage or gliding 

 planes. When the metal is much strained a sec- 

 ond system of bands appears on some of the 

 grains, crossing the first system at an angle, 

 and in some cases showing little steps where the 

 lines cross. These bands are considered due to 

 VOL. xxxix. 31 A 



slips occurring in a second set of cleavage or 

 gliding surfaces. Occasionally a third system of 

 bands may be seen. When UK: experiment is 

 made with a polished but unetched specimen the 

 slip bands appear equally well. The boundaries 

 of the grains are invisible before; straining, but 

 they can be distinguished as the strain proceeds, 

 for the slip bands form a cross hatching that 

 serves to mark out the surface of each grain. 

 The slip bands are developed by compression as 

 well as by extension. They appear, when an iron 

 bar is twisted well beyond the elastic limit, for 

 the most part in directions parallel and perpen- 

 dicular to the axis of twist. A strip of sheet 

 metal in the soft state when bent and unbent in 

 the fingers shows them well developed by the 

 extension and compression of the surface. They 

 have been developed by the authors in iron, steel, 

 copper, silver, gold, nickel, bismuth, tin, gun 

 metal, and brass. They are more difficult to ob- 

 serve in carbon steels than in wrought iron. The 

 experiments are believed to throw a new light 

 on the character of plastic strain in metals and 

 other irregular crystalline aggregates, showing 

 that plasticity is due to slip on the part of the 

 crystals along cleavage or gliding surfaces. It 

 is inferred that " flow " or nonelastic deforma- 

 tion in metals occurs through slips within each 

 crystalline grain of portions of the crystal on one 

 another along surfaces of cleavage or gliding 

 surfaces. 



In a paper on the diffusion of elements in iron 

 Prof. J. Oliver Arnold and A. M. William re- 

 marked that Sir J. Lowthian Bell and Sir Fred- 

 erick Abel had shown many years ago that if 

 steel and wrought iron were placed in close con- 

 tact and heated the iron gained and the steel 

 lost carbon. They then referred to a series of 

 experiments made by Prof. Campbell, of Michi- 

 gan, on the diffusion of sulphur through hot iron. 

 This author's results were not concordant, but 

 some of his data and the conclusion he deduced 

 from them were so startling and improbable that 

 his work was hardly deemed worthy of serious 

 discussion by theoretical metallurgists. He had 

 stated that pure sulphide of iron would not dif- 

 fuse through hot iron, but that oxysulphide of 

 iron diffused through it unchanged without con- 

 taminating the metal. He had therefore pointed 

 out that the fact of a triple compound thus rap- 

 idly diffusing deprived of all its cogency the doc- 

 trine that because carbon diffused it must neces- 

 sarily do so in a state of elementary solution. 

 By experiments upon samples furnished by Prof. 

 Campbell, illustrating each stage of his work, 

 the authors had found that, although he seemed 

 in error with reference to the nondiffusive power 

 of pure sulphide of iron, the accuracy of his gen- 

 eral conclusions was confirmed, and that he had 

 made an important discovery in metallurgical 

 physics. Sir W. C. Roberts- Austen had shown in 

 1896 that on fusing gold plates to the bases of 

 bars of lead the gold-lead alloy interpenetrated 

 the lead bars when they were maintained for some 

 time at a temperature of 250 C. a point well 

 below the melting point of lead and he had 

 proved that at the end of a month the gold-lead 

 alloy had actually traveled up to the top of the 

 lead bars, a distance of not less than 2f inches. 

 These results suggested to the authors the prob- 

 ability of similar molecular migrations taking 

 place in the compounds of the elements fixing 

 in that complex metal called steel. It was neces- 

 sary to conduct experiments involving the main- 

 tenance of steel at a full red heat for many hours 

 in a vacuum, so as to avoid oxidation effects 

 an object for which a very simple and efficient 



