96 Dilute Acids mid PJwsjjhorus Compounds in the Soil 



This is the equation of a straight line. If, therefore, log y is plotted 

 against log (7 all the points ought to lie on a line. The figures show 

 that they do so. 



2. Sodium phosphate was added but the soil was not subjected to 

 any preliminary treatment ; instead the amount of extractable PgOg was 

 determined. This value flus the amount of added PgOg gives the total 

 y + C. C being determined by analysis, y is known by simple sub- 

 traction. 



Table VI. ^2^5 contained in successive 24 hour periods of diffusion 

 in N/10 HCl. The results are calculated as a percentage of the soil. 



Soils 



Hoos 10 



Hoos2C 



AgdeU 



Teynham 



Saxmundhara* 



t 

 Woburn 



10-13 



•004 



■0128 



•0048 



•0087 



•003 



•0043 



•0067 



* Plot 6 (unmanured). 



t Plot 4 (superphosphate). 



In determining the total extractable P2O5 it is obviously necessary 

 to eliminate the reverse reaction. This is done by a diffusion process. 

 The ordinary diffusion thimble is not satisfactory for soil, and no 

 muslin is fine enough to hold it together and keep it out of the diffusion 

 liquid. The soil was therefore shaken with 2 % agar solution, and 

 then cast into solid sticks by pouring into a glass tube of 10 mm. 

 diameter and 100mm. in length; these sticks can be placed in dilute 

 acids, and they allow of rapid diffusion without disintegration. In 

 carrying out the experiment 5 to 10 gms. of soil and 30 c.c. of agar 



