Report of the Committee on Physical Analyses, 1954–55, Soil Science Society of America

nnnE Standing Committee on Physical Analyses re-L ported several years ago (SSSA Proc. 13:575-576, 1949) that the hydrometer method of particle size analysis was a popular procedure in soil laboratories, despite certain well-known limitations. Hydrometer methods are less accurate than the pipette method, but are sufficiently accurate for many purposes. Their chief advantages are speed and convenience. The discovery and early development was due to G. J. Bouyoucos, who has done much towards making the hydrometer a practical laboratory device for particle size analysis (see (2) and (3) for recent recommendations of Bouyoucos). Hydrometer methods have received wide acceptance by engineering testing laboratories as a result of the physical theory developed by Arthur Casagrande of Harvard University (4). Casagrande's method has received theoretical and experimental support from the work of several investigators (5, 6, 7, 8, 11), and has been recommended by the American Society for Testin Materials (1). The procedure described herein follows Casagrande's theory and is similar to, but not identical with, the ASTM procedure (1). It has been reviewed by the committee and accepted as a basis for further study. The committee wishes to give further consideration to the type of dispersion and to the precision of the method. Comments and results of tests made by others will be gladly received by the committee.