HIGH-PRESSURE PHYSICS — BRIDGMAN 



207 



below the discontinuity the lattice arrangement is the same face- 

 centered, close-packed arrangement. The presumption is therefore 

 again that there must be an inner electronic change, although the theo- 

 retical details have not yet been worked out. 



In figure 4 the volume changes of some of the ordinary solid elements 

 are shown as a function of pressure in the range up to 100,000 atmos- 

 pheres. There is a great variability in compressibility. The most 



20 40 60 80 100 



Figure 4.- — The change of relative volume of a number of substances shown as a function 

 of pressure up to 100,000 kg./cm.^ (metric atmospheres). 



compressible element shown in the diagram is cesium, which at 

 100,000 atmospheres is compressed to 37 percent of its initial volume. 

 The least compressible substance is probably carbon in the form of 

 diamond, which under the same pressure is compressed only to 98.2 

 percent of its initial volume. The diagram indicates that for most 

 substances the loss of volume is far from being linearly related to 

 the pressure; the lines are strongly curved, showing that the com- 

 pressibility drops off with increasing pressure. This is the same effect 

 as we noted for liquids, but it is on a different and much more exten- 



