88 



SOILS: PROPERTIES AND MANAGEMENT 



f 



quantity of soil is used, the mass is not kept properly 

 agitated ; secondly, convex currents are set up in the 

 conical glass tube, which vitiates the results ; and, thirdly, 

 the separate particles tend to coalesce into granules. It 

 is evident that in any separation of soil particles all 

 granulation must be avoided. This is usually accom- 

 plished by shaking or boiling the 

 ,/jL sample previous to the determi- 



nation. The tendency toward 

 granulation during the process 

 of separation itself is fatal to 

 JL^Y_— j! accuracy, as compound particles 



carrying a large number of small 

 grains would fail to pass over 

 at water-current velocities cor- 

 responding to their component 

 parts. 



66. Hilgard's churn elutriator. 

 — The errors of the Schone ap- 

 paratus are obviated to some 

 extent by Hilgard's, 1 the prin- 

 ciple of operation remaining ex- 

 actly the same. In Hilgard's 

 elutriator the deflocculated soil 

 sample is introduced into the 

 base of a cylindrical tube (see 

 Fig. 12) in which is placed a 

 rapidly revolving stirrer. This 

 is designed to counteract convex 

 currents and to prevent the 



Fig. 12. — Hilgard's churn 

 elutriator for mechanical 

 soil analysis of particles 

 above .01 mm. in diameter, 

 (e), Intake; (p), stirrer; 

 (c), screen; (a), separating 

 chamber ; (o), outlet tube. 



1 Hilgard, E. W. Methods of Physical and Chemical Soil 

 Analysis. Ann. Rept. California Agr. Exp. Sta., pp. 241-257. 

 1891-1892. 



