METHODS OF DETERMINING WEIGHT PER UNIT VOLUME 359 



wards admitted, and the specimens left standing for several hours in the water 

 at atmospheric pressure. When the pores are very small, it is advisable to 

 leave standing 24 hours, as they fill very slowly.'" 



A -full discussion of refinements is given bv Melcher. 9 



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Figure 1. — Diagram showing by Ordinate* the Weight in Tons per cubic Meters and Per 

 < ent of Moisture absorbable of Sediments of Porosity indicated by Abscissas 



In this the customary range of porosity is assumed to be between 25.05 per cent and 

 47.64 per cent, as shown, and the specific gravity of the minerals is supposed to average 

 2.<S. The average results for fresh taken glacial brick clay and the same dried are indi- 

 cated by dots. 



Work of Charles C. Moore 



The address of Moore above cited 2 gives the theoretical packing of 

 spheres based on the well known work of Schlichter, in the Nineteenth 

 Annual Eeport of the United States Geological Survey, and others, and 

 he also gives 129 tests of the mineral specific gravity G m and porosity, 

 from which the volume weight can be figured. He discusses the increas- 

 ing density of sandstone near a fault, of slate near a contact, of a sill 

 near its center, and various iron ores, a subject which Mead has fully 

 treated, bringing out points of interest to geologists. 



The theoretical w T ork may be condensed as follows (it being a com- 

 posite of the results of Schlichter, Moore, Harker, and Reade) : 



A. Spheres all equal Size (a) 



Porosity, 

 per cent. 



1. Spheres arranged at corners of cubes 47 . 64 



2. Closest hexagonal packing on horizontal, radius of sphere (a), ver- 



tical tiers directly over each other 39 . 54 



.°». Closest packing in two planes. . . .*. 30.18 



