OF THE HYDROSTATIC PRESS. 139 



with so much precision, as to prevent the escape of water between 

 their surfaces, without increasing the friction to such a degree, that it 

 would require a very great force to counterbalance it. 



In order, therefore, to render the piston water-tight, and to prevent 

 as much as possible the increase of friction, recourse must be had to 

 other principles, which we now proceed to explain. 



The piston D is surrounded by a collar of pump leather oo, repre- 

 sented in Jig. 5, which collar being doubled up, so Fig. 5. 

 as in some measure to resemble a lesser cup placed 

 within a greater, it is fitted into a cell made for its 

 reception in the interior of the cylinder ; and when 



there, the two parts are prevented from coming toge- ^^m^ 

 ther, by means of the copper ring pp, represented in Ft S- 6 - 



Jig. 6, being inserted between the folds, and retained in its place, by a 

 lodgement made for that purpose on the interior of the cylinder. 



The leather collar is kept down by means of a brass or bell-metal 

 ring mm, Jig. 7, which ring is received into a Fig. 7. 



recess formed round the interior of the cylinder, 

 and the circular aperture is fitted to admit the 

 piston D to pass through it, without materially 

 increasing the effects of friction, which ought to be 

 avoided as much as possible. 



The leather is thus confined in a cell, with the edge of the inner 

 fold applied to the piston D, while the edge of the outer fold is in 

 contact with the cylinder all around its interior circumference ; in 

 this situation, the pressure of the water acting between the folds of 

 the leather, forces the edges into close contact with both the cylinder 

 and piston, and renders the whole water-tight ; for if the leather be 

 properly constructed and rightly fitted into its place, it is almost 

 impossible that any of the fluid can escape; for the greater the 

 pressure, the closer will the leather be applied to both the piston and 

 the cylinder. 



The metal ring mm is truly turned in a lathe, and the cavity in 

 which it is placed is formed with the same geometrical accuracy ; but 

 in order to fix it in its cell, it is cut into five pieces by a very fine 

 saw, as represented by the lines in the diagram, which are drawn 

 across the surface of the ring. The four segments which radiate to 

 the centre are put in first, then the segment formed by the parallel 

 kerfs, (the copper ring pp and the leather collar oo being previously 

 introduced), and lastly, the piston which carries the pressing table. 



That part of the cylinder above the ring mm, where the inner 



