528 



EXPERIMENT STATION RECORD. 



The conclusion was reached from this work that " the use of a 1 

 per cent solution of citric acid does not assist us very materially more 

 than concentrated hydrochloric acid in actually reaching a duplication 

 of the measure of solvent activity proceeding in nature, nor thus in 

 estimating the proportion of the soil elements that are immediately 

 available as plant food." 



It was believed that the use of weaker solvents acting for longer 

 periods would give more satisfactory results. After various prelim- 

 inary tests the following method was adopted: 



"Exactly 200 gin. of soil was put into the ordinary 2-liter acid bottles, having 

 ground-glass stoppers, and 200 cc. of the solvent added. This volume was found to 

 he just enough about to saturate and immerse the soil, without any great excess of 

 the solvent solution being present, which was guarded against. 



"Twenty bottles were taken and charged with 200 gm. of soil and 200 cc. of sol- 

 vent, as already stated. Ten of these bottles were given to observations on upland 

 (mauka) soils, and the remaining 10 bottles to corresponding observations on low- 

 land (makai) soils. 



" Each series of 10 bottles was further divided into 2 groups of 5 bottles each. The 

 one group was to furnish data setting forth the results of the continued action of a 

 tV P er cen * solution of [citric] acid, and the second group of a -,-' - per cent solu- 

 tion of acid upon the same soil. . . . One bottle from each of the 4 groups, con- 

 taining 5 bottles each, was selected for testing and controlling the acidity of the 

 bottles in the 4 groups. . . . 



" The control of the acidity of the solutions was made by the use of a ^ v normal 

 solution of sodic hydrate. Every fourth day 25 cc. of solution was drawn with a 

 pipette from each of the 4 'test bottles' and the remaining acidity of the solution 

 determined, when enough citric acid was added to restore the acidity of the solu- 

 tions in each bottle in all the groups to the original strength." 



The results obtained by this method are given in the following 

 table : 



Solubility of constituents of upland and lowland soils in water and in citric acid of different 



strengths. 



Calcium 

 oxid. 



Potas- 

 sium 

 oxid. 



Phos- 

 phoric 

 acid. 



Ferric 



and 



aluminic 



oxids. 



Silica. 



UPLAND SOILS. 



In jV per cent citric acid : 



12 days 



33 days 



78 days 



103 days 



In E l ff per cent citric acid : 



12 days 



33 days 



78 days 



103 days 



In water : 



2 days 



120 days 



LOWLAND SOILS. 



In T ^j per cent citric acid : 



12 days 



33 days 



78 days 



103 days 



Percent. 



0.0131 

 .0257 

 .0240 

 .0202 



.0097 

 .0136 

 .0129 

 .0125 



.0032 

 . 0097 



.0175 

 .0400 

 . 0221 

 . 0234 



Per cent. 



0.0132 



.0264 



.0181 



.0175 



. 0223 

 .0146 

 .0186 



.0033 



.0149 



.0203 

 .0291 

 . 0306 

 .0207 



Per cent. 



0. 0008 



.0008 



.0019 



.0028 



.0008 

 .0009 

 .0011 

 .0015 



.0001 

 .0007 



. 0007 

 . 0010 

 .0015 

 .0018 



Per cent. 



Per cent. 



0. 1089 

 .0878 



. 0279 

 .0268 



.0527 

 .0288 



0. 0046 



.0041 

 .0046 



.0067 



