66 TOWERS AND TANKS FOR WATER-WORKS. 



any service where good wearing surfaces are desired. Mild 

 steel has superior welding properties as compared with hard 

 steel, and will endure higher heat without injury. Steel 

 below .10 per cent, carbon should be capable of doubling 

 flat without fracture after being chilled from a red heat in cold 

 water. Steel of . 1 5 per cent, carbon will occasionally submit to 

 the same treatment, but will usually bend around a curve 

 whose radius is equal to the thickness of the specimen ; 

 about 90 per cent, of specimens stand the latter bending- 

 test without fracture. As the steel becomes harder, its 

 ability to endure this bending-test becomes more exceptional, 

 and when the carbon ratio becomes .20 per cent., little over 

 25 per cent, of specimens will stand the last-described bend- 

 ing-test. Steel having about .40 per cent, carbon will usually 

 harden sufficiently to cut soft iron and maintain an edge." 



The classification of steel seems to the average layman a 

 little arbitrary. As shown in the preceding quotation, " For 

 convenient distinguishing terms, it is customary to classify 

 steel in three grades, etc." The classification according to 

 the manufacturers' standard specifications is that " Steel shall 

 be of four grades: ' extra soft,' ' fire-box,' ' flange or boiler,' 

 and ' boiler-rivet ' steel. Commercially, and as nuoted in the 

 trades papers, the classification is as follows: 'tank,' 'shell,' 

 ' flange,' ' ordinary fire-box,' and ' locomotive fire-box.' ' 



In reply to an inquiry as to the average physical and 

 chemical properties of each of the commercial grades, one of 

 the largest testing-laboratories in the United States writes as 

 follows: "While we, of course, keep records of all tests 

 made by us, they are not tabulated nor averaged. We 

 doubtless have on record several hundred thousand tests of 

 all grades of material made from nearly all the different steel 

 works in the country. We can, however, give you approxi- 

 mately what the different grades of steel run, as follows: 





