OF THE HYDROSTATIC PRESS. 141 



ing to the fancy of the projector, but in the figure before us the per- 

 foration is in the side. 



The tube thus furnished, is forcibly pressed into its seat by a hollow 

 screw w, called an union screw, which fits into another screw of equal 

 thread made in the cavity of the cylinder ; the joint is made water- 

 tight, by means of a collar of leather, interposed between the end of 

 the tube and the bottom of the cavity. 



A similar mode of connection is employed in fastening the tube to 

 the forcing pump, the description of which, although it constitutes an 

 important portion of the apparatus, does not properly belong to this 

 place ; the principles of its construction and mode of action, must 

 therefore be supposed as known, until we come to treat of the con- 

 struction and operation of pumps in general. 



Admitting therefore, that the action of the forcing pump is under- 

 stood, it only now remains to explain the nature of its operation in 

 connection with the Hydrostatic Press, the construction of which we 

 have so copiously exemplified. 



148. In order to understand the operation of the press, we must 

 conceive the piston D Jig. 1, as being at its lowest possible position in 

 the cylinder, and the body or substance to be pressed, placed upon the 

 crown or pressing table E ; then it is manifest, that if water be forced 

 along the tube b b b by means of the forcing pump, it will enter the 

 chamber of the cylinder F immediately beneath the piston D, and cause 

 it to rise a distance proportioned to the quantity of fluid that has been 

 injected, and with a force, determinable by the ratio between the square 

 of the diameter of the cylinder and that of the forcing pump. The 

 piston thus ascending, carries its crown, and consequently, the load 

 along with it, and by repeating the operation, more water is injected, 

 and the piston continues to ascend, till the body comes into contact 

 with the head of the frame B, when the pressure begins ; thus it is 

 manifest, that by continuing the process, the pressure may be carried 

 to any extent at pleasure ; but we have already stated, in developing 

 the theory, that there are limits, beyond which, with a given bore 

 and a given thickness of metal, it would be unsafe to continue the 

 strain. 



When the press has performed its office, and it becomes necessary 

 to relieve the action, the discharging valve, placed in the furniture 

 of the forcing pump, must be opened, which will admit the water to 

 escape out of the cylinder and return to the cistern, while the table 

 and piston, by means of their own weight, return to their original 

 position. 



