Agricultur. — Horticultur. — Forstbotanik. 575 



geneous in nature, its mass will not affect the concentration attained 

 by the Solution." 



The paper describes in detail the methods employed and the 

 results obtained in experiments undertaken to ascertain the con- 

 ditions of the Solution of soil phosphats and kindred substances, 

 both in the soil itself and in the laboratory processes for soil ana- 

 lysis. Solls were extracted continuously with 1 per cent. citric acid. 

 The portion was subjected to the action of the solvent and kept in 

 continuous movements in a shaker for twenty hours. The So- 

 lution was withdrawn and a fresh supply of the solvent allowed to 

 act under similar conditions, and so on for as many times as re- 

 quired. 



The general conclusions of the authors are: 



1. The solvent does not at once remove all the phosphoric acid 

 capable of going into Solution in the particular solvent em- 

 ployed; instead an equilibrium is established between the phos- 

 phoric acid in the solvent and in the soil. 



2. The concentration of the Solution in equilibrium with the soil 

 falls with each successive attack on the soil by the same 

 solvent. This indicates the presence in the soil of several 

 Compounds of varying solubility. The mass of the more so- 

 luble being small and of the same order as the amounts 

 going into Solution in the eariier extracts. When these more 

 soluble Compounds have been removed, an approximate con- 

 stant equilibrium is attained between the phosphoric acid re- 

 maining in the soil and that going into Solution at each 

 extraction, indicating that after the more soluble Compounds 

 have been removed there remains a phosphate in each soil 

 of such low solubility that the amount going into Solution 

 at each extraction is independent of the mass present in 

 the soil, 



3. With soils which have been for many years manured with a 

 particular phosphate, the amounts of phosphoric acid going 

 into Solution in successive extractions with 1 per cent. citric 

 acid Solution follow a logarithmic law of decrement, indicating 

 the presence of one particular phosphate which dissolves in 

 Proportion to the mass of it present in the soil. This law 

 does not, however, hold good for ordinary soils which have 

 been recently manured. 



4. In the case of the Rothamsted soils, the sum of the phos- 

 phoric acid dissolved out by the first five extractions with 

 citric acid approximates very closely to the known surplus of 

 phosphoric acid accumulated by the additions of manure to 

 the soil. 



5. Assuming that the solvent actions of the soil water and of 

 the weak acid solvents employed in the laboratory are com- 

 parable, the evidence lends no support to the theory that all 

 soils give rise to a natural soil Solution of approximately con- 

 stant composition, which is not dlstributed by the use of ferti- 

 lisers containing phosphoric acid. 



6. For the practical purposes of soil analysis, the evidence af- 

 forded by a Single extraction of the soil for twenty hours 

 with continual shaking is very similar to that obtained frorn 

 a series of successive extractions by the same solvent and 

 leads to the same conclusions as to the manurial requirements 

 of the soil. W. G. Freeman. 



