BRIDGMAN. — HIGH PRESSURE EXPERIMENTING. 



633 



^ 



^ 



B 



-C 



^A 



used. The reason is that under high pressure rubber becomes rigid 

 and brittle Hke glass, and under the right conditions may even crack. 

 If the rubber is initially so small that under the high pressure its 

 natural volume compression would make it smaller 

 than the hole, then it would certainly leak if it 

 were not for the excess pressure in the packing 

 over that in the liquid. But the rigidity of the 

 rubber may become so great that the excess pres- 

 sure is not sufficient to force it tightly against the 

 walls of the cylinder, unless the rubber would of 

 itself completely fill the hole at the high pressure. 

 The form of plug to be used during the prelim- 

 inary seasoning of the apparatus is essentially the 

 form described above so modified as to allow it to 

 follow the stretching of the cylinder. It could be 

 used under all circumstances, except that the fric- 

 tion is considerably higher than that of the other 

 form. It is shown in Figure 6. The possibility 

 of distension of the head to follow the stretching 

 of the cylinder is provided by a coned ring of 

 copper, A, backed with solder, B, and the possi- 

 bility of stretching at the upper end is provided by using a washer 

 of soft steel, C, rather deeply cupped, the groove of the cup being 

 filled with a solder. With such a plug, a pressure of 2.5000 kgm/cm.^ 

 may be maintained in a cylinder which has stretched ^ of an inch. 



Figure 6. Piston 

 packing for high 

 pressures for use in 

 seasoning the cylin- 

 ders when provision 

 must be made for 

 stretch of the cylin- 

 der without leak 

 The scale of the 

 diagram is * actual 

 size. 



The Cylinders. 



The cylinders, or "bombs," need to be subjected to a seasoning 

 process, because the pressures at which they are to be used are beyond 

 the natural elastic limit of the steel. It is, therefore, necessary to 

 raise the elastic limit by the application of a stress beyond the original 

 elastic limit. But since the application of a stress great enough to 

 permanently raise the elastic limit produces a permanent distortion 

 of the cylinder, the cylinder must be machined again to the final 

 size after the preliminary stretching. 



The choice of steel for the cylinder is a matter of much importance. 

 A high tensile strength, combined with a moderate elongation before 

 rupture is essential. The Krupp Chrome Nickel steel mentioned for 

 the piston is satisfactory for this purpose, or somewhat better is a 



