November 4, 1921] 



SCIENCE 



439 



soil in a cylinder provided with an outlet at 

 the bottom. The ethyl alcohol is then poured 

 on top of the soil column and as it penetrates 

 the soil it displaces some of the soil solution 

 which forms a zone of saturation below the 

 alcohol. This zone increases in depth as it is 

 continually forced downward by the alcohol. 

 When the saturated zone reaches the bottom 

 of the soil column the soil solution, free of 

 alcohol, drops from the soil as gravitational 

 water. 



The only apparatus required is a cylinder 

 in which to pack the soil. Brass soil tubes or 

 glass percolators were used for this purpose. 

 The diameter of the tube and the height of 

 the soil column determine the rate and time 

 required for displacement. 



The soil was packed in the cylinders by 

 means of a short wooden rod. No difficulty 

 was experienced in obtaining uniform pack- 

 ing. The degree of packing required for the 

 best results is determined by the kind of soil 

 and its moisture content. Sands and peats 

 can be packed very firmly, but witli heavier 

 soils care must be taken that they are not 

 puddled in packing, in which 'case displace- 

 ment is exceedingly slow or entirely pre- 

 vented. To prevent puddling it is best to use 

 the heavier soils at moisture contents slightly 

 below their optimum for plant growth. After 

 a little experience one can readily determine 

 tJie proper degree of packing for any soil at 

 a given moisture content. 



The time required for displacement varies 

 widely depending on the moisture content of 

 the soil, the degree of packing, the soil type, 

 and the height of the soil column. In most 

 cases it is possible to complete the displace- 

 ment in one day, often in a much shorter 

 time, if the soil column is not over twelve to 

 fifteen inches in height. However, in some 

 cases it required several days to complete the 

 displacement. 



It is practicable to obtain 35 to 45 per cent, 

 of the soil solution by this method. However, 

 it is possible to displace a much larger per- 

 centage of the soil solution than this. Using 

 a silt loam soil at a moisture content of 23.3 

 per cent, a 75.6 per cent, displacement has 



been secured. Istcherekov reports that with a 

 soil at saturation it is possible to displace 

 about 95 per cent, of the soil solution before 

 the appearance of alcohol. 



The method has been successfully used on 

 a number of soils including sands, loams, 

 clays and peats. The results obtained indi- 

 cate that the true soil solution is secured. 

 Successive portions of the displaced solution 

 have the same composition as is indicated 

 by total salt and freezing point determina- 

 tions. It is probable that the solution obtain- 

 ed is a true aliquot of the entire soil solution, 

 that is, the displaced solution is of the same 

 composition as the portion remaining in the 

 soil. A comparison was made of the amount 

 of total salts and nitrates obtained by the dis- 

 placement metliod and by a 1:5 water ex- 

 traction of the soil. The results given in 

 Table I. shows that the two methods give ap- 

 proximately the same amount of total salts. 

 The results for nitrate nitrogen are the same 

 within experimental error. 



TABLE I 



Total Salts and Nitrate Nitrogen in the Dry Soil 

 as determined by the Two Methods 



NO, Total 



P.P.M. Nitrogen P.P.M. Salts 

 Water Displace- Water Displace- 

 KindofSoll Extract ment Extract ment 



Clay loam 71.5 75.2 796 747 



Clay 29.4 24.7 370 306 



Sand 18.7 22.4 205 275 



Sand 57.0 61.2 1,400 1,512 



Silt loam 10.8 9.7 223 161 



Silt loam 79.8 71.0 732 648 



Silt loam 48.3 54.5 506 512 



Although the displacement method has re- 

 ceived only slight recognition, the writer be- 

 lieves it has many possibilities. It seems to 

 offer an opportunity for a more careful study 

 of the concentration, composition, and reac- 

 tion of the soil solution. A more complete 

 knowledge of the changes that take place in 

 the soil solution should aid in the solution of 

 many of the problems of the soil fertility, 

 plant nutrition, and related subjects. 



F. W. Parker 



Univebsity of Wisconsin 



