The Flow of Marble. 429 



turned doT^Ti, so as to be somewhat thinner imme- 

 diately around the marble. Into either end of the 

 tube, containing the column, an accurately fitting steel 

 plug or piston was then inserted, and by means of 

 these the pressure was applied. The high pressure 

 required was obtained by means of a powerful press, 

 especially constructed for the purpose, consisting of 

 a double hydraulic " intensifier," the water pressure 

 being in the first instance obtained from the city 

 mains. By means of this machine, pressures up to 

 13,000 atmospheres could be exerted on the columns 

 having a diameter of 0.8 inch, and the pressures could 

 be readily regulated and maintained at a constant 

 value for months at a time, if required. 



It having been ascertained that the columns of 

 the marble 1 inch in diameter and 1^ inch in height 

 crushed at a pressure of from 11,430 to 12,026 lbs. to 

 the square inch, the column enclosed in its wrought- 

 iron tube, in the manner above described, was placed 

 in the machine and. the pressure applied gradually, 

 the exterior diameter of the tube being accurately 

 measured at frequent intervals. Xo effect was notice- 

 able until a pressure upon the marble, varying of 

 course with the thickness of the enclosing tube, but 

 generally about 18,000 lbs. to the square inch, was 

 reached ; when the tube was found to slowly bulge, 

 the bulge being symmetrical and confined to that 

 portion of the tube surrounding the marble. The 

 distension was allowed to increase until the tube 

 showed signs of rupture, when the pressure was 

 removed and the experiment concluded. The condi- 

 tions under which the marble was submitted to 

 pressure were four in number : — 



1. At the ordinary temperature in the absence of 



moisture. (Cold drv crush.) 

 32 



