622 FRANK D. ADAMS AND J. AUSTEN BANCROFT 



Such being the case, with the information thus secured it is 

 possible to separate the two components of the load, namely, that 

 necessary to overcome the resistance offered by the tube and that 

 required to effect the deformation of the marble. If at a series of 

 points the load required to produce a certain distension or bulge 

 in the steel tube when filled with the tallow is subtracted from the 

 load required to produce the same bulge in the case of the tube con- 

 taining the marble, values are obtained which represent that por- 

 tion of the load which is expended in affecting the deformation of 

 the marble. This may be termed the true curve, and that obtained 

 for a standard column of Carrara marble deformed in a standard 

 steel tube having a wall thickness of 0.25 centimeter is shown in 

 Fig. 7. In the same manner the true curve for each of the other 

 rocks may be plotted from the data presented in Tables I and II. 

 It will be seen that, in the case of Carrara marble, this curve start- 

 ing from a distension of 0.00 1, which may be considered to be due 

 to elastic deformation, and which is produced by a load of 12,000 

 pounds, shows a rapid deflection to a point representing a distension 

 of 0.052 which is produced by a load of 33,000 pounds, after which 

 it develops into what is practically a straight line until the tube 

 ruptures. 



This shows that after the elastic limit of the marble has been 

 passed, at about 12,000 pounds, and the marble commences to 

 deform, the load which is required to start this movement and 

 produce a unit of diametral expansion is relatively great. As the 

 movement progresses the additional increment of load required to 

 produce a unit of diametral expansion grows progressively less till 

 a bulge of 0.052 is reached, after which there is a definite and con- 

 stant ratio between the increase of load and the expansion which 

 it produces. This ratio is 0.0065 for each increase of 1,000 pounds 

 in load. 



It will be noted that in the case of the slate, just after the rock 

 began to deform, the curve shows a sudden break or sag which is 

 repeated at a second point before the regular movement, indicated 

 by the nearly straight line, is developed. This is due to the fact, 

 above mentioned, that the slate, being a foliated and not a granular 

 rock, is not isotropic in its response to pressure. It consists of little 



