694 



Subsurface Geologic Methods 



in which a is the areal extent assigned to a sample 

 / is the fractional porosity of a sample 

 t is the thickness of the interval assigned to a sample, and 

 n is the total number of samples 



Permeability 



The permeability of a porous rock is a measure of its ability to 

 permit the penetration, movement, and passage-through of fluids. Quan- 



Graduated Copillory »■ 



Expansion Chamber — »! 



Sample Chamber 

 Clamp 



Counterbalance- - 



Chambe for Weight 



-Pulley 



Leveling Bulb 



Mercury 



— Track Clamp 



— Track 



— Rubber Hose 



Splash Pan for Hg. 



Floor Line 



Figure 373. Washburn-Bunting type porosimeter used 

 at University of Texas. 



titatively the definition of permeability is based upon the empirical re- 

 lation between pertinent variables which is known as Darcy's law.^^ 

 Darcy's law, based upon experimentation, states that the velocity of a 

 homogeneous fluid through a porous medium is directly proportional 



^' Darcy, Henri, Les Fountains publiques de la ville de Dijon, Victor Dalmont, Paris, 1856. 



