274 



TKSTIXC OF CHAINS. 



maximum load which this machine is capable of is 

 100,0001bs., and it will test chains up to 5ft. long and 

 lin. diameter. The machine is made by Messrs. Green- 

 wood & Batley. 



In some cases, in addition to the tests which have 

 been mentioned, links are cut from the chain, opened, 

 and straightened under heat, and afterwards tested as 

 bars in the usual way. After the inspection under the 

 proof load any defective links should be taken out of the 

 chain and' replaced by sound ones. 



The following is an example of a complete test of 

 a lin. iron chain intended to be used for lifting pur- 

 poses : * 



TESTS FOR HARDNESS. 



143. The hardness of a metal may be best de- 

 scribed as the resistance which the particular metal 

 offers to permanent strain or plastic deformation, it 

 being understood that brittle metals, such as cast iron, 

 do not come within this definition. Various means 

 have been employed by which to determine the relative 

 hardness of different substances. Of these, some of 

 the earliest methods employed were made to depend, 

 either upon the possibility of one substance being able 

 to produce a scratch upon some other substance, or upon 

 the relative ease with which a standard substance would 

 produce a scratch upon the material in question. Another 

 kind of test for hardness is made to depend upon the 

 volume of a standard body which can be forced into 

 the surface of the given material by the application 

 of a standard load for a given length of time. In 

 the method used by Col. Rodman, of the United States, 

 the quantity of material displaced by the expenditure of 

 a standard quantity of mechanical work in forcing a hard 

 steel diamond point into the material to be tested was 



*Engineer, October, 1898, p. 365. 



