INTERNAL FRICTION IN ROCKS 605 



to the middle portion of the column, which is surrounded by the 

 thinner portion of the tube. The pistons being inserted and the 

 whole properly set up in the testing machine, the pressure was 



Fig. 2. — Steel cylinder, inclosing a rock column and with the two extensometers 

 in position, set up in the Wicksteed press. To the right a bulged cylinder is shown 

 as it appears at the close of an experiment. 



applied in successive increments of 1,000 pounds. The exten- 

 someter showed no yielding of the inclosed rock until a load of about 

 12,000 pounds had been reached, when a very slight distension of 



