TABLE OF CONTENTS 



IX 



82 Actual weight of a soil, 83 Pore space in soil, 84 

 The number of soil particles, 85 Surface exposed 

 by soil particles, 86 The effective mean diameter of 

 soil particles, 87. 



CHAPTER VIII 



THE ORGANIC MATTER OF THE SOIL 



The source and distribution of organic matter, 88 

 Composition of plants, 89 Decay of organic matter in 

 soils, 90 Composition of soil humus, 91 The work of 

 Oswald Schreiner, 92 Toxic material in the soil, 93 

 End products of humus decay, 94 Carbonized mate- 

 rials of soil, 95 The estimation of soil organic matter, 

 96 The estimation of soil humus, 97 The organic 

 content of representative soils, 98 The humus content 

 of soil, 99 The influence joi the original material on 

 the resultant Tiuinus, 100 Effects of organic matter on 

 Maintenance of soil organic matter, 102. 



126-152 



CHAPTER IX 

 >-THE COLLOIDAL MATTER OF SOILS 153-169 



The colloidal state, 103 The properties of colloids, 

 104 Colloidal phases, 105 Flocculation, 106 Com- 

 mon soil colloids and their generation, 107 Prepara- 

 tion of colloids, 108 Colloids and soil properties, 109 



Factors affecting colloids, 110 Estimation of col- 

 loidal content, 111. 



CHAPTER X 



L STRUCTURE 170-197 



Plasticity, 112 The cause of plasticity, 113 The 

 importance of plasticity, 114 Cohesion, 115 Methods 

 of determining cohesion, 116 Factors affecting cohe- 

 sion, 117 Moisture limits for successful tillage, 118 

 Control of cohesion and plasticity, 119 Soil tilth, 120 



Granulation, 121 Forces facilitating granulation, 

 122 Wetting and drying, 123 Freezing and thawing, 



