WATER-CONTENT 



27 



than I per cent from the dug sample used as a check. As soon as dug, the 

 core is pressed out of the geotome by the plunger directly into an air-tight 

 soil can. Bottles may be used as containers, but tin cans are lighter and 

 more durable. Aluminum cans have been devised for this purpose, but on 

 account of the expense, "Antikamnia" cans have been used instead. These 

 are tested, and those that are not water-tight are rejected, although it has 

 been found that, even in these, ordinary soils do not lose an appreciable 

 amount of water in twenty-four hours. The lid should be screwed on as 

 quickly as possible, and, as an added precaution, the cans are kept in a close 

 case until they have been weighed. The cans are numbered consecutively 

 on both lid and side in such a way that the number may be read at a glance. 

 The numbers are painted, as a label wears off too rapidly, and scratched 

 numbers are not quickly 

 discerned. 



44. Weighing. Al- 

 though soil samples 

 have -been kept in tight 

 cans outside of cases 

 for several days without 

 losing a milligram of 

 moisture, the safest plan 

 is to make it a rule to 

 weigh cans as quickly 

 as possible after bring- 

 ing them in from the 

 field. Moreover, when 

 delicate balances are 

 available, it is a good 

 practice to weigh to the 

 milligram. At remote 

 bases, however, and 

 particularly in the field, 

 and on reconnaissance, where delicate, expensive instruments are out of 

 .place, coarser balances, which weigh accurately to one centigram, give 

 satisfactory results. The study of efficient water-content values has already 

 gone far enough to indicate that differences less than i per cent are neg- 

 ligible. Indeed, the soil variation in a single square meter is often as 

 great as this. The greatest difference possible in the third place, i. e., that 

 of 9 milligrams, does not produce a difference of .1 of i per cent in 

 the water-content value. In consequence, such strong portable balances 

 as Bausch & Lomb 12308 ($2), which can be carried anywhere, give entirely 



Fig. 4. Field balance. 



