126 A TREATISE ON METAMORPHISM. 



size, and arranged "so that the lines joining their centers form cubes,'" 1 this 

 will be the most open possible arrangement. In this case the pore, space 

 will be 47.64 per cent. 6 



King has made a number of experimental determinations of the pore 

 space of unconsolidated sands, of broken rocks, and soils, the material being- 

 packed as closely as he was able to pack it. Where quartz sand com- 

 prising materials varying greatly in coarseness was used, a pore space as 

 low as 25.43 per cent was obtained/ But ," well-rounded grains of nearly 

 uniform diameter tend to give a pore space which lies between 32 and 40 

 per cent. * * * For simple sands with angular grains the pore space is 

 much larger than it is for the rounded sands of the same size of grains, and 

 in the case of the crushed glass, whose grains are more angular than those 

 of the crushed limestone, which have a tendency to be cuboidal in form, 

 the pore space is the largest of all." e 



Seelheim found that clays when allowed to settle in water have a pore 

 space of 50 to 79 per cent, and that there is no sensible reduction of this 

 space under a pressure of 30 meters of water/ 



In clay loams and clays pore spaces as high as 48 to 52 per cent were 

 obtained by King." He suggests that the high pore space of clays may 

 oossibly be partly explained by the angularity of the grains, it being well 

 known that the very fine mechanical sediments are largely composed of 

 angular particles.'' 



It is evident from these experimental results of King's that the grains 

 of sands and soil are not packed by nature in the most compact manner 

 possible; otherwise the pore spaces would run lower, rather than higher, 

 than Slichter's minimum pore space (25.95 per cent); for the natural grains 



"Slichter, cit, , p. 308. 



&Slichter, cit., p. 309. 



<-' In order to get the closest packing, the material was added "in small lots at a time and gently 

 tamped with a broad, flat-faced pestle until the vessel was filled. . . . The vessel, after being filled 

 by tamping, was ' struck off ' with a piece of plate glass, then held firmly while with light blows the 

 walls of the tubes were struck gently, but repeatedly, as long as any reduction in volume could be 

 produced."— King, F. H., Principles and conditions of the movements of ground water: Nineteenth 

 Ann. Kept. U. S. Geol. Survey, pt. 2, 1899, p. 208. 



<*King, cit,, p. 211. 



«King, cit., p. 215. 



/Seelheim, Zeitsc.hr. fiir anal. Chemie, vol. 19, p. 387; cited in King, F. H., Principles and con- 

 ditions of the movements of ground water: Nineteenth Ann. Rept. U. S. Geol. Survey, pt. 2, 1899, p. 78. 



ffKing, cit., pp. 213-215. 



''King, cit, pp. 217-218. 



