Texture of Soils. 117 



of pore space would be occupied to the extent of 7 

 per cent, in the first case and of 52.36 per cent, in the 

 second case. Such a condition would leave only about 

 6.73 per cent, of pore space for the closest packing. 



Such arrangements as this are not likely of course to 

 occur in nature but in the construction of macadam roads 

 and in all concrete work a definite effort is made to reduce 

 the pore space to the smallest possible limit by using 

 crushed rock, gravel, sand and finally cement to fill alJ 

 pores as completely as possible. 



139. Number of Soil Grains per Unit Weight. If soil 

 grains were all spheres and in a given case they were all 

 of the same size the number in a gram could be found by 

 the equation 



Weight of soil 

 ha of grains = a^X Bp.gr. 



6 



where the weight of the soil is in grams and the diameter 

 of the soil grains, d, is in c. m. 



In the table below are given in round numbers the num- 

 ber of grains in one gram and in one pound of soil, sup- 

 posing the grains all spheres and to have a specific gravity 

 of 2.65. 



That is to say, 720 multiplied by 10 used as a factor 3, 

 6, 9 and 12 times gives the number of grains in a gram 

 of soil in round numbers and the number in a pound may 

 be found by using 10 as a factor in the same way and 

 the number 326,903. 



If the soil were made up of some grains of all the sizes 

 8 



