in the rock. The other factor, surface area, is directly related to grain size and 

 grain angularity. The ratio of porosity to surface area is of critical importance. 

 The advantages of determining these factors are that on the basis of rock com- 

 position, a suitable detergent may be selected without time-consuming trial-and- 

 error methods. From textural analysis, the most efficient rate of withdrawal or 

 displacement of fluid may be estimated. 



Universal Stage Techniques 



The universal stage greatly extends petrographic investigations in that it 

 permits study of pertinent features that are beyond the capacity of the normal 



Figure 4-5. Setup for universal stage work. 



69 



