28 Journal of Agricultural Research voi. xiii, no. i 



of soils in place. Though definite conclusions from so few correlations 

 are not warranted, it seems that the moisture equivalent represents 

 more nearly the maximum capillary capacity of the soil in place than 

 do the ordinary laboratory determinations upon the disturbed soil, 

 both in point of accuracy and of absolute value. 



PART II.— A NEW METHOD OF DETERMINING THE VOLUME WEIGHTS 



OF SOILS 



RUBBER-TUBE METHOD 



In order to ascertain accurately by means of moisture determina- 

 tions the volume of irrigation water which a given volume of soil absorbs 

 and retains, it is obviously necessary to know with a fair degree of 

 accuracy the volume weight of the soil in place. It was believed early 

 in these studies and has since been verified that the ordinary method 

 of determining volume weight of samples of disturbed soil could not be 

 relied on. The use of an iron cylinder to be driven into the soil for 

 determining its volume weight in place was considered. It was concluded 

 that this method was unsatisfactory because of the tendency of the 

 soil below the cylinder to become compacted and thus be driven ahead 

 of, instead of into, the cylinder, and because of the time and expense 

 involved m taking very many samples to the depths which must be con- 

 sidered in the soils of the arid regions. The first objection applies espe- 

 cially to the use of cylinders of small diameter, such as the King soil tube, 

 and the second to larger tubes, with which the first objection may be 

 measurably overcome. 



The need of devising a new method which would overcome these 

 objections seemed sufficiently urgent to warrant attention. The soil 

 samples used for making moisture determinations were secured by the 

 use of a 2-inch auger of the post-hole type. The diameter of the tip 

 or cutting edge of the bowl of the auger used was slightly greater than 

 that of the base, a fact which suggested that practically no displace- 

 ment of soil by lateral thrust or compacting ahead of the auger would 

 be caused by boring. 



Upon the basis of these assumptions it was necessary only to devise 

 a means of accurately measuring the volume of the hole made by a 

 6-foot boring in order to get a satisfactory measure of the volume weight of 

 the soil, since the total amount of soil taken from the hole 2 inches in 

 diameter and 6 feet deep could very conveniently be taken to the labo- 

 ratory, dried, and weighed. Various methods of measuring the volume 

 of the auger hole were considered. It was attempted to measure the 

 diameter of the hole at different depths by means of calipers and thus 

 compute the volume, but this proved unsatisfactory. Finally it was 

 conceived that an accurate measurement of the volume could be obtained 

 by inserting a very thin-walled elastic rubber tube into the auger hole 



