METHODS OF DETERMINING WEIGHT PER UNIT VOLUME 357 



water, it is found that usable results may be had. For instance, let us 

 adopt the following symbols, using Melcher's symbols and Mead's names 

 as far as possible. Mead does not discriminate between the wet and the 

 dried-out ore or the shrinkage in volume. This is small in ores, but may 

 be 15 per cent in clays. 



Let G m = mineral specific gravity (usually 2.6 to 3.0) — that is, that 

 which is obtained by pycnometer on the powder or by noting how many 

 grams of powder it takes to add to a burette of water 1 centimeter in 

 volume. 



Let D = density of dry porous material, tons per cubic meter ; also 

 called W v . 



Let d refer to a dry sample; 

 w refer to a wet sample; 



p refer to a sample coated with paraffin or to the coating ; 

 s refer to a sample Submerged in water. 



For example, W w p s means the weight of a wet (saturated) sample 

 coated with paraffin and submerged in water. 



V w p a refers to the volume occupied by the same. 



G is the weight per unit volume of the material as a whole. 



G d = W d / V d and is > than D of Mead, owing to shrinkage in drying. 



D = G m (l — P w )=W d ./V w . 



P w = porosity of wet rock in place = (W w — W d ) / V w . 



M = moisture of saturation expressed as a percentage of the wet 

 weight = P w / G w = P w / (G m (1 — P w ) + P w ) . 



M is in sediment usually about half of P w . 



Now we measure : Illustrative Example 



(1) W w = weight of freshly taken or satu- 15 . 5 

 rated sample 



(2) W( w p ) = weight coated with paraffin 16.4 



(3) W( w p s ) = weight of paraffin-coated 7.3 

 sample in water 



Let W w p — W w = W p = the weight of . 9 



paraffin 



Assuming specific weight of paraffin to 

 be .9, W p = .9 V p and V p = 1. 



W w p — W w p s = V w p, which is 9.1 



G W = W W /V W 



= W w / V w p — Vp, thus subtracting 1 . 



= W W /W WP — W wps — l.iWp 16.5-1-8.1 = 1.92 



