486 University of California Publications in Agricultural Sciences [Vol.3 



The residue constituted the main portion of the 0.25 mm. hydraulic value sep- 

 arate. The residue from the 6 to 8 minute decantation was placed in the elutri- 

 ator, and separated by the usual method into the various sizes. Since, however, 

 the sample was not prepared by boiling previous to the separation of the clay, the 

 clay was never as thoroughly removed from the coarser particles and the finer 

 aggregate particles were not completely broken down. Hence when the sample 

 was placed in the elutriator and subjected to the violent agitation of the stirrer 

 an appreciable amount of clay passed off with the finest separate. Therefore, 

 instead of allowing the water to return to the carboy from the settling bottle, 

 during the running off of the finest separate, the following procedure was em- 

 ployed: The water was run into precipitating jars and allowed to stand for 24 

 hours, and the clay water was then decanted off and boiled down with the other 

 clay water. 



A further modification of the Hilgard method was found advisable after the 

 change from the large elutriator tube to the small one, preparatory to running off 

 the coarser separates. The mechanical defects in the elutriator always allowed 

 for the collection of a portion of the sample in crevices where the stream of Avater 

 could not reach to carry off the particles. Hence, when the large tube was 

 removed, and cleaned, there was found an appreciable amount of the finer sedi- 

 ments that had not passed over. These were all added to the small tube of the 

 elutriator, and the additional material of the smaller sizes run off, using an hour 

 or so for each size. This seemed a better method than the separation of such 

 sediments by the beaker method, as was done by Dr. Loughridge. 



The separates, after decanting most of the water, were dried first on the water 

 bath and later in the drying oven at 100°C-110°C and weighed. All of the deter- 

 minations were made on the water free basis. 49 



Additional Physical Determinations 



Upon the surface or A horizon samples of the 24 soils considered in this study 

 additional physical determinations were made by the Division of Soil Technology, 

 through the courtesy of Professor Charles F. Shaw. These determinations were 

 of the mechanical analysis by the Bureau of Soils method, 50 of the moisture equiva- 

 lent by the Briggs and McLane method, 51 and of the hygroscopic coefficient accord- 

 ing to Hilgard 's method. 52 



Chemical Methods 



At first the chemical w T ork was based upon the "strong acid extraction" 

 method, so well known through the work of Dr. Hilgard."' 3 There are some very 

 pertinent objections, as well as advantages, to the method of acid extraction for 

 the purpose of comparing soils among themselves. 51 



In the analysis 2.5 gram samples, air dry, were used throughout. The acid 

 extraction results are not included in this paper. 



49 The writer wishes to emphasize the tedium of the elutriator process, and to advise 

 strongly against the use of the apparatus for the comparison of the soils as to texture. The 

 elutriator is excellent from a theoretical point of view, but the results do not at all warrant 

 the extravagant use of time in the laboratory that the apparatus requires. 



r,0 U. S. Bur. Soils, Bull. 84, 1912. 



51 Ibid., Bull. 45, 1907; Proc. Amer. Soc. Agron., vol. 2 (1910), pp. 133-47. 



52 Calif. Agr. Exp. Sta., Circ. 6 (1903), p. 17; Soils, pp. 197-99. 

 "Calif. Agr. Exp. Sta., Circ. 6 (1903), pp. 16ff; Soils, pp. 340ff. 

 54 See Hissink, Intern. Mitt, fur Bodenkunde, vol. 5 (1915), no. 1. 



