32 The Philippine Journal of Science i9i6 



ing the relation between the strength of a prism to the strength 

 of a cube, using Bauschinger's data, is 



strength of prism _ ^ ,^^g ^^22 1 



strength of cube h 



in which d equals the least lateral diameter and h equals the 

 height of the prism. The equation shows that the strength of 

 a prism having a height twice as great as its least lateral 

 diameter is only 88.9 per cent of that shown by a cube. Cubes 

 are very generally used in making compressive tests, but their 

 use is not to be recommended. Not only do they give results 

 that are too high in calculating the factor of safety, but since 

 the theoretical angle of rupture approaches 60° and not 45°, as 

 was formerly thought to be the case, it is apparent that the 



/Vix 



ratio between the height and the least lateral dimension y^j 



should have a minimum of not less than 1.5, so that failure 

 may proceed along the normal angle. Bauschinger has made 

 a very careful and detailed study of this problem,^* and the con- 

 clusions cited are inferred from data obtained during the inves- 

 tigation of a uniformly fine-textured sandstone. 



A cylindrical specimen possesses a very desirable feature over 

 a cubical one in that there is an absence of the numerous edges 

 and sharp corners characteristic of the cube. With cylindrical 

 specimens, molding operations are simplified, there is less danger 

 of getting a defective test piece, and, finally, there is less pos- 

 sibility of injury during manipulation. 



CHARACTERISTICS OF MATERIAL 



In this investigation three or four compression specimens 

 were made for each test; the results shown in the table were 

 obtained by taking the average of at least three breaks. In 

 the tensile tests a minimum of eleven briquettes were broken at 

 each test ; in some instances, seventeen. As was to be expected, 

 the compression results were much more uniform than the 



mens with the height twice the least lateral diameter, gave results that 



fitted the equation. The cylindrical shape with r-="p gave strengths 



varying from 60 per cent to 80 per cent of the strengths shown by the 

 cubical specimens. Not enough tests were made to calculate an accurate 

 constant for this tuff, but the results obtained were sufficiently significant 

 to indicate that Bauschinger's equation is applicable. 



^•^ Bauschinger, J., Mitt. a. d. Mech. Tech. Lab. d. k. Tech. Hochschule, 

 Muenchen (1876), 6. 



