OF THE HYDROSTATIC PRESS. 121 



And the practical rule for the determination of D, may be expressed 

 in words as follows. 



RULE. Multiply the pressure on the piston of the cylinder, 

 by the square of the diameter of the forcing pump, and divide 

 the product by the force with which the plunger descends ; 

 then, the square root of the quotient will be the diameter of 

 the cylinder sought. 



127. EXAMPLE 4. The diameter of the cylinder is 5 inches, and 

 the force with which the plunger descends, is equivalent to 750 Ibs. ; 

 what must be the diameter of the forcing pump, in order to transmit 

 a pressure of 18750 Ibs. to the piston of the cylinder ? 



Here we have given D r= 5 inches ; p 750 Ibs., and P zz 18750 

 Ibs. ; consequently, by substitution, equation (88) becomes 



1 8750 d* = 750 X 5 2 , 

 and by division, we shall have 

 750 X 25 



therefore, by extracting the square root, we get 



d /f zzl inch. 



If both sides of the original equation marked (88), be divided by 

 P, and the square root extracted, the entire pressure on the piston, 

 the general expression for the value of d becomes 



= /l/ "P"' (92). 



And the practical rule which this equation supplies, may be 

 expressed in words in the following manner. 



RULE. Multiply the force with which the plunger descends, 

 by the square of the diameter of the cylinder, and divide the 

 product by the entire pressure on the piston; then, extract 

 the square root of the quotient for the diameter of the forcing 

 pump. 



128. The foregoing is the theory of the Hydrostatic Press, as 

 restricted to the consideration of the diameters of the cylinder and 

 forcing pump, and the respective pressures on the piston and plunger; 

 but since the instrument is generally furnished with an indicator or 



