PHILIPPINE SOILS. 313 



need both drainage and irrigation for crops of the latter type, such as 

 sugar cane, coconuts or hemp. In general, it would not be f economical to 

 grow sugar cane on a soil that has too little retentive power for moisture, 

 nor on a soil which is so impervious as to require drainage, any more 

 than it would be economical to gi'ow rice on a very sandy soil with a 

 porous subsoil, because of the excessive amount of water necessary. I 

 believe that in the Philippines most soils consisting of a sandy loam to 

 a loamy clay will prodiice almost any crop abundantly if the water sup- 

 ply is carefully controlled, while the light, sandy soils should be res^ 

 tricted for the present to crops which do well with little water, such as 

 peanuts or mulberries and the heavy or clayey soils utilized for the culti- 

 vation of rice. 



For the determination of physical composition of soils the centrifugal method, 

 practically as outlined in. the I'fnited States Department of Agriculture, Biu-eau 

 of Soils, Bulletin Number 24, has been used in this laboratory and gives fairly 

 concordant results." 



Unpublished analyses by this method are given in Table IX. Those by the 

 Schone method in Table XVII. 



METHOD OF PHYSICAL ANALYSIS. 



"V^Tiile fairly satisfactory in the hands of trained men, the centrifugal 

 method allows of a large personal equation. In this country where we 

 have oriental assistants without technical training, any method which 

 may be reduced to an empirical one is most advantageous and permits the 

 saving of much time. Schone's method is superior in this respect. 



Schone's method " depends on the separation of soil into particles of various 

 sizes by the use of a stream of water moving A^ertically and regulated by a piezo- 

 meter so as just to equal the resistance of the largest particles intended to be 

 removed. This resistance depends on the form and also on the specific gravity of 

 the grains and in order to calculate its value normals for these factors must be 

 assumed, namely, the form of a sphere and the specific gravity of quartz (2.65). 

 According to Newton's law of gravity Schone worked out a formula which might 

 serve to solve the problem whether by this or that velocity of the current (v) 

 silt particles of this or that diameter will be removed, that is, that in a given 

 case, the velocity of the current in the apparatus is just sufficient to counteract 

 the tendency of a given particle to sink; all particles of a smaller diameter will be 

 carried on by the current, while all of a greater diameter will settle out. Objection 

 has been raised to this method on the ground that the silt particles vary too much 

 in specific gravity to permit of any one value being taken as the specific gravity of 

 the whole. The results of analysis show that the application is not rigid and in 

 order to have the theoretical formula agree with the analysis it has to be modi- 

 fied empirically to read d=VTiX0-0314 mm, where d is the diameter of the 

 silt particle. I have checked this empirical formula with the aid of a microscope 

 and a stage micrometer and have concluded that it is as accurate as any method 

 yet proposed. 



"Pratt, This Journal, Sec. A (1911), 6, 35. 



"Ueber Schlammanalyse, Bull, de la Soc. imperiale des naturalistes de Moscow 

 (1867), 40, Pt. I, 324; Ztschr. f. analyt. Chem. (1868), 7, 29; Wiley, H. W., 

 Principles and Practice of Agricultural Analysis, Easton, Pa., 2nd ed. (1906), 

 1, 231. In compiling the description of the apparatus all of these have been used. 



