space or grain-volume measurements. Calipering is the most rapid method of 

 bulk-volume determination. It is readily adapted to any type of rock that can 

 be drilled or cut to definite size and is the only method available for vuggy 

 material in which the larger vugs on the exterior surface of the specimen are 

 an integral part of the pore space. 



Determination of Pore Volume 



(1) Measurement of Pore Volume By the Washburn-Bunting Porosimeter 



This instrument (fig. 12-1) is very popular in many laboratories in which 

 a large number of samples are handled daily. It is the most widely used of 

 that class of porosimeters in which the sample is evacuated and the air trapped 

 and measured. The sample is placed on the surface of the mercury in the 

 enlarged portion of the instrument; the upper half is firmly seated with a ground- 

 glass joint; and the mercury is raised to completely surround the sample and 

 fill the graduated portion to and just slightly above the stopcock, which is then 

 closed. The mercury column is lowered 3 or 4 feet below the sample chamber 

 for a definite period of time, then raised to trap the air in the graduated neck. 

 The mercury columns are balanced and the volume of trapped air, minus a pre- 

 determined correction factor, is the pore volume of the sample. 



(2) Measurement of Pore Volume By Mercury Injection 



This is another rapid and popular method of pore-volume determination 

 used by several laboratories when a large number of samples are to be processed. 

 The mercury porometer (fig. 12-2) is an expensive instrument but combines 

 both bulk-volume and pore-volume measurements in one operation. In principle 

 the instrument is a high-pressure mercury pump calibrated in cubic centimeters 

 per turn and fitted with a sample chamber that can be vented to the atmosphere. 

 The bulk volume of the sample is measured by the difference between the volume 

 of mercury required to fill the empty chamber and the volume required to fill 

 the chamber and sample at atmopheric pressure. The vent is then closed, and 

 the chamber and sample are pressured to a predetermined arbitrary reading. 

 The volume of mercury forced into the sample, suitably corrected for compres- 

 sibility, is the pore volume. 



Determination of Grain Volume 



(1) Measurement of Grain Volume By Determination of the Grain Density 



The extracted and dried sample is weighed and saturated with a liquid, 

 and the weight of the saturated sample while immersed in the same liquid is 

 determined. The grain volume is equal to the difference between the dry weight 

 and the saturated submerged weight divided by the density of the saturant. 

 An alternative method, used primarily to estimate or check on the measured 



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