NpVEMBEE 27, 1896.] 



SCIENCE. 



783 



they continue in a permanent condition of 

 tension. 



Steel is the only metal that combines elas- 

 ticity and tenacity in such high degree as to 

 warrant its advantageous use in the man- 

 ner just described. For gun metal the ma- 

 terial should be manganese steel, made from 

 the purest wrought iron attainable, with a 

 very small percentage of carbon, indeed not 

 more than one per cent. This should be so 

 uniformly diffused as to secure the closest 

 possible approach to absolute homogeneity* 

 The elastic limit should not be reached for 

 any stress under 50,000 pounds per square 

 inch, nor should the ultimate strength be 

 less than 100,000 pounds per square inch. 

 Such steel withstands a high temperature 

 without softening, resists erosion well, and 

 permits but little set under shock beyond 

 the elastic limit. The preparation of such 

 metal is a severe test of skill for the metal- 

 lurgist. The most conspicuously success- 

 ful gunmaker in the world, Friedrich 

 Krupp, of Essen, Germany, uses crucible 

 steel exclusively for this purpose. This 

 firm, founded by the grandfather of its pres- 

 ent head, has made a specialty of steel and 

 its applications in manufacture during the 

 last eighty-five years. Bessemer, open- 

 hearth, and crucible steel plants are all in- 

 cluded in its outfit. Much the most ex- 

 pensive product among these is crucible 

 steel. In its manufacture the skill of the 

 fathers has been given to their sons ; and 

 doubtless grandsons and great-grandsons 

 will continue to apply the secrets of their 

 special art in the same place. With the 

 staid conservatism of the laboring classes in 

 Germany the development of heredity in 

 artisan skill is not uncommon. In America 

 so restless, impatient and ambitious are our 

 laborers that the son rarely ever lives in 

 the same place or works at the same occu- 

 pation with his father. 



So highly developed is the crucible steel 

 industry at Essen that ingots of this metal 



weighing each as much as seventy tons 

 have been repeatedly cast, and with these 

 the forgings are made from which Krupp 

 constructs his monster guns. Many visi- 

 tors at the Columbian Exposition looked 

 with astonishment at the great gun weigh- 

 ing one hundred and twenty tons, which 

 was only one of several of the same size due 

 to this firm. In other parts of the world 

 crucible steel is abundantly produced for 

 cutlery, and for small articles generally 

 where the finest quality is demanded. 

 But nowhere else than in Essen has the 

 highest grade of crucible steel been made 

 thus far in quantities suflBcient for the 

 largest forgings. In England, in France, 

 and in America gun metal is at present 

 made by the open hearth process. While 

 this product is greatly superior to Bessemer 

 steel the method of production is such as to 

 forbid the attainment of such nearly perfect 

 homogeneity as can be secured by the more 

 expensive crucible method. 



The open hearth steel used for our larg- 

 est American guns is produced for the 

 most part, if not entirely, at Midvale and 

 Bethlehem in Pennsylvania. Before actual 

 use test specimens are required to manifest 

 tensile strengths from 75,000 to 125,000 

 pounds, and elastic limits from 40,000 to 

 70,000 pounds, per square inch, according to 

 the calibre of the gun and the special parts 

 of this for which the metal is intended. 

 For tubes, jackets and hoops the maximum 

 tensile strength demanded is 93,000, and 

 the maximum elastic limit, 53,000 pounds 

 per square inch. 



Up to ten years ago American fortifica- 

 tions were for the most part supplied with 

 nothing superior to the Rodman cast-iron 

 smooth-bore columbiad and Parrott rifle, 

 the latter being made of cast iron but re- 

 enforced with a wrought-iron hoop. Dur- 

 ing this interval Congress has appropriated 

 about $20,000,000 for the modernizing of 

 our navy and our seacoast defences. For 



