82 METHODS OF DETERMINING ALKALI 



trading the solutions with oil or by pressure or centrif- 

 ugal force, which are not in general use as yet, the great 

 drawback being that little more than the free water can 

 be obtained. 



King and his associates in their studies of soil nitrates 

 used a method which, with a number of amendments, has 

 been used extensively by later investigators. Schreiner 

 and Failyer (9) describe a modification of this method 

 which has probably been used more widely than any other. 

 They discuss it as follows : 



"If comparable results are to be obtained, it is essential 

 in preparing the soil extract to follow as nearly as practical 

 a uniform procedure. The volume of water used and the 

 time of its action are necessarily conventional. The ratio 

 of five parts of water to one part of soil has been adopted 

 in procuring solutions of the readily water-soluble salts 

 in many of the soil studies. The mixture is agitated three 

 minutes and allowed to stand twenty minutes before 

 filtering. The exact procedure when the soil to be ex- 

 amined is still in the moist state as collected in the field 

 varies slightly from that when it is air-dried or oven- 

 dried. All results, however, are stated on a uniform basis, 

 preferably on the dry soil. The results from a moist soil 

 are not comparable with those obtained from a dried soil, 

 although both be stated in terms of dry soil, owing to the 

 fact that dried soils give a somewhat greater concentra- 

 tion of soluble salts in the soil extract. 



"From Moist Soil. The moist samples taken from 

 typical and comparable portions of the field are well broken 

 up and mixed in a granite-ware basin or porcelain dish. 

 Two 100-gram portions of this composite are then weighed 

 out on a balance capable of weighing accurately to within 

 0.1 gram. One of these portions is for the moisture de- 



