THE MECHANICAL ANALYSIS OF SOIL. 



By Wallace E. Pbatt. 



{From the Division of Mines, and the Laboratory of General, Inorganic and 

 Physical Chemistry, Bureau of Science, Manila, P. I.) 



A soil survey of the sugar lands of the Island of Negros, Philippine 

 Islands, has been made by Mr. Herbert S. Walker/ formerly of the 

 Chemical Laboratory of this Bureau, necessitating a large number of 

 mechanical soil analyses. Some modifications of the usual methods have 

 been devised and are given in this paper, together with a few analytical 

 results. 



Mechanical analysis consists of separating the "fine earth" portion of 

 soil into its individual grains or particles, and of placing these grains, 

 according to their size, in groups the limits of which are established 

 arbitrarily, with a view to ease of separation and the importance of 

 the grain size of each to the general soil character. The Bureau 

 of Soils of the United States Department of Agriculture have carefully 

 outlined the general method as practical by them.- They divide the 

 soil into seven groups, as follows : 



Group 

 No. 



Separated by- 



Conventional name. 



Diameter of 

 grains. 



Screen ! Fine gravel 



do Coarse sand 



do I Medium sand .. 



do Fine sand 



do Very fine sand . 



Sedimentation 

 Centrifuge 



mm. 

 2.0 -1.0 

 1. -0. 5 

 0. 6 -0. 25 

 0.25-0.10 

 0. 10-0. 05 



Silt ' 0. 05-0. 005 



Clay I <0.005 



Xothing above 2 millimeters in diameter enters into the analysis, 

 because usually the same sample is employed for the mechanical as well 

 as for the chemical analysis. The samples for the mechanical analyses 



'The Sugar Industry in the Island of Negros, Bureau of Science, Manila, 1910, 

 Pub. P. I. Bur. Science (1910) Bulletin. 



-Bull. V. S. Dept. Agric, Bur. Soils (1904), No. 24. 



35 



