182 CAST-IRON BEAMS. 



The measurements of the dimensions of the beam should 

 be made at the actual point of fracture after the specimen 

 has been broken. The nature of the fracture should be 

 referred to in the report, and a statement made as to 

 whether it is "fine-grained" or "coarse-grained," "sound '" 

 or otherwise. 



The deflection of a cast-iron beam of these dimensions 

 will be found to be roughly one-tenth of an inch for each 

 1,000 Ib. of load. 



The equivalent load on a 2 in. by 1 in. section may be more 

 readily obtained by making use of a table of multipliers, 

 calculated for sections of various dimensions ; or by means 

 of the accompanying diagram (Fig. 89.) The use of this 

 diagram can be best explained by showing how it is applied 

 to the above case. 



Here the depth and width were respectively 2 - 03 in. 

 and T04 in., and the actual breaking load 3,125 Ib. 



To use the diagram, first look along the base line and 

 find the vertical ordinate corresponding to 1'04 in. Then 

 follow this ordinate upwards until it meets the one of the 

 sloping lines corresponding to the depth. Then the height 

 of this point, measured along the ordinate to the vertical 

 scale of the diagram, will give a number with which to 

 divide the load, in order to obtain the equivalent load. 



In the present case, this is 1'072. So that the equiva- 

 lent breaking load on a 2 in. by 1 in. section is 



which is the same result as was obtained by the previous 

 method. 



The test which has just been described is of the 

 kind which is carried out for purely commercial pur- 

 poses. A test of a similar cast-iron beam under more 

 complete conditions, so as to provide detailed informa- 

 tion as to the properties of the metal, will now be 

 described. The span is supposed to be the same as before, 

 and the section is again approximately 2 in. by 1 in. In 

 the present instance, however, the increments of load are 

 relatively small, and the deflections are measured at much 

 more frequent intervals in order to determine the modulus 

 of elasticity with accuracy. In a case of this sort the 

 deflections must be measured by means of a deflectometer, 

 of the form indicated on Fig. 86, page 176. The 

 actual process of making this test is as follows : The beam, 



