196 A. F. GUSTAFSON 



Organic carbon was determined by the Parr bomb-calorimeter method, 

 CO2 was measured and reduced to standard P and T from which C was cal- 

 culated. C X 1.724 (Wolff factor) gives organic matter. This is not claimed 

 to be absolutely accurate nor strictly comparable since the carbon content 

 of soil organic matter varies with its age and the conditions under which de- 

 composition has occurred. The organic matter in white silt loam, for example, 

 is probably more highly carbonized than that in brown silt loam and that in 

 drab clay, a swamp soil, has been affected by a different type of decom- 

 position from bro^\^l silt loam, a well-drained type. However, the figure for 

 organic matter is of value in a comparative way when, as in these soils, the 

 differences between them are marked. 



Procedure 



The soils were air-dried, worked over with a rolling pin, passed through a 2-nun. screen, 

 thoroughly mixed and divided into three portions, a, b, and c. On samples of a the usual de- 

 terminations of total soluble solids and nitrates were made in the original air-dry and in the 

 water-free condition. To b distilled water was added, and worked by hand, until it reached 

 what might be termed "optimum" moisture content when the soil was placed in 2-liter ear- 

 thenware jars. These were weighed on a solution scale the next day and at the end of each 

 succeedmg 7-day period, when distilled water was added to restore that lost by evaporation. 

 To c, in similar jars, distilled water was added to a point of saturation and more water 

 was poured on as needed to keep the soil submerged. Then b and c were kept in the labor- 

 atory for nine weeks, except the Dunkirk sandy loam which was kept only 8 weeks. The 

 regular determinations were made on both moist and water-free samples at the end of this 

 time. 



Results are given in table 6. 



Table 6 has several outstanding features. The increase in total solids ex- 

 tracted from soils 1, 2 and 3, well supplied with organic matter, when the 

 original air-dry soil is dried in the oven at 105°C. is very marked; in soils 4, 5 

 and 6, low in organic matter, the actual increase due to drying is less, but the 

 amount of soluble solids varies from nearly twice to almost three times as 

 much as that in the air-dry soil. In all, except white silt loam, which is very 

 low in organic matter, the moist b samples kept 9 weeks at optimum moisture- 

 content had a higher quantity of soluble material than did the air-dry soil, 

 and the dry b soil exceeded that water-freed directly from the original air-dry 

 condition. This increase may be accounted for by the increase in nitrates, 

 calculated as Ca(N03)2- 



The saturated c samples in the wet condition showed more total soluble 

 salts than either of the others, even though the nitrates had disappeared. 

 When oven-dried, this soil showed the highest soluble salt content in five of 

 the six soils, and the sixth was but 0.8 mgm. below the next higher soil, the 

 water-freed, moist Dunkirk sandy loam. This may be accounted for in part 

 by the very large amount of water in these soils shown in table 6 to be 75.7 

 per cent in drab clay down to 37.8 per cent in Dunkirk sandy loam. Here 

 the soil solution is much more dilute and more solids tend to dissolve, as the 



