STRENGTH OF MATERIALS 



5592 



STRINDBERG 



terials differ greatly in this regard. Several 

 sorts of stress are usually distinguished. There 

 is a tensile, or stretching, stress, and resistance 

 to this direct pull is known as tensile strength. 

 Compressive strength is resistance to such 

 crushing masses as pillars support. Shearing 

 strength is resistance to forces acting trans- 

 versely to the material. In addition to these 

 there is a torsional, or twisting, stress, but this 

 is really a combination of the larger classes first 

 named. Still other stresses are occasionally dis- 

 tinguished. 



Ingenious machines have been devised for 

 testing the strength of materials, the strain ap- 

 plied being that to which the material will be 

 most subjected when in place. Materials are 

 said to have elasticity, and this limit of elas- 

 ticity is not exceeded as long as the material 

 resumes its shape when the stress is removed. 

 When, however, the material becomes "set," it 

 is said to have reached the yield point; and in 

 building, the stress at the yield point, rather 

 than the breaking point, is what concerns the 

 contractor. 



Steel and wrought iron offer the stoutest re- 

 sistance to pulling strains. Wood, which does 

 not suffer a great tensile stress, has what is 

 known as a greater elastic range than steel or 

 iron; that is, it bends more under a given 

 pressure. The strength of wood depends upon 

 its weight, the heavier woods being usually 

 also the stronger. Most materials will with- 

 stand a severer crushing than pulling strain, 

 but this is not true of wood. Cast iron will 

 withstand a very heavy crushing strain, and 

 for that reason it is commonly employed in 

 the spans of bridges and in the foundations of 

 modern buildings. The tenacity of materials 

 is put to a harder test under twisting strains 

 than any other. In order to combine strength 

 with lightness, materials are often cast in hol- 

 low form. 



The strength of materials can be expressed in 

 figures with only a rough approximation to 

 exactness, because the strength varies with dif- 

 ferent specimens. In engineering work, actual 

 tests determine the fitness of any material to 

 withstand the stress to which it will be sub- 

 jected. The tensile strength of such woods 'as 

 white oak and chestnut is about 12,000 pounds 

 to the square inch; that of hemlock, red oak 

 and white pine, about 8,000 pounds. The 

 crushing strength of white oak is about 8,000 

 pounds to the square inch and that of the other 

 woods mentioned between 5,000 and 8,000 

 pounds. Portland cement has a tensile strength 



of about 700 pounds to the square inch, and 

 ordinary structural steel has a tensile strength 

 of from 60,000 to 70,000 pounds per square 

 inch. The table of estimates given below was 

 prepared by William C. Unwin, an English 

 authority on the subject: 



STRENGTH OF MATERIALS, IN POUNDS, PER SQUARE 

 INCH 



Consult Merriman's Strength of Materials; 

 Burr's Elasticity and Resistance of the Materials 

 of Engineering. 



STRIKE, the action of a body of laborers in 

 ceasing work in order to force an employer to 

 grant their labor demands. It has always been 

 the chief weapon of labor organizations. When 

 employees leave their work, not because of dis- 

 satisfaction with their own condition, but to 

 make their employer bring pressure upon an- 

 other employer whose laborers have already 

 struck, their act is known as a sympathetic 

 strike. A general strike, such as occurred in 

 Italy in 1914, is a political protest participated 

 in by all the laborers in a country. A lockout 

 is the reverse of a strike; that is, it usually re- 

 sults from a strike and is the refusal of an 

 employer to permit his employees to work until 

 they have submitted to his terms. 



Consult Sorel's Reflections on Violence; Adams 

 and Sumner's Labor Problems. 



Related Subjects. The reader is referred to 

 the following articles in these volumes : 

 Eight-Hour Day Open Shop 



Labor Organizations Sweatshop System 



STRIND'BERG, AUGUST (1849-1912), one of 

 the foremost Swedish writers of modern times. 

 His literary output is difficult to classify be- 

 cause it represents such a variety of interests 

 and so many schools of thought. A man of ex- 

 traordinary mental energy, he was constantly 

 stimulated by a craving to investigate new in- 



