CAST IROX. 



385 



It is also to be noted that for crushing specimens of 

 equal cross section the shorter pieces may be expected to 

 yield the higher results. 



Hodgkinson gives the following values for the com- 

 pressive strength of cast iron : 



HODGKINSON'S TESTS (From " Rules and Tables," Clark). 



Stirling's iron is cast iron melted with wrought iron. 



205. Cross Breaking Strength of Cast Iron. The 



most common test for cast iron is that under a transverse 

 load. This is so, both because the test can easily be carried 

 out with simple appliances, and also because the results 

 given are more likely to be uniform and reliable than those 

 in pure tension. The sizes specified for this test are either 

 lin. X lin. X 12in. span, or 2in. deep X lin. wide X 36in. 

 span, and for the latter dimensions the central load which 

 the bar is specified to stand varies from 25cwts. to 30cwts. 

 It has already been pointed out that the beam formula 

 for rectangular beams, 



does not hold except in cases where the material is elastic. 

 In the case of cast iron it is found that the maximum 

 stress, as given by the above formula, when calculated 

 from the central breaking load, exceeds to a considerable 

 extent the tensile stress found for the same iron from 

 A3 



