20 Liquid Manure. 



The changes which took place in the chemical constitution of 

 the liquid manure in contact with this soil are similar to those 

 noticed in the first and second experiment. It will be seen, 

 however, that the power of this loamy soil to absorb ammonia 

 and potash is not equal to that exhibited by the pasture land and 

 by the calcareous clay from Cirencester. Thus, in the experi- 

 ment before us, 20,000 grains of loamy fertile soil absorbed 9'74 

 grains of ammonia ; or 1000 grains absorbed *487 ; whilst 1000 

 grains of Cirencester soil absorbed *738 of ammonia, and 1000 

 grains of pasture land, -737. 



We also find a smaller proportion of potash retained by the 

 loamy soil than by the Cirencester soil and by the pasture land. 

 Tt thus seems probable that soils which absorb much ammonia 

 also absorb much potash. 



Again, we find that some lime, though sparingly present in 

 the soil, is taken up by the liquid manure ; and that nearly the 

 total amount of chloride of sodium of the original liquid passes 

 unaltered into the liquid which was left in contact with this soil 

 for three days. Other minor changes may be passed over 

 unnoticed, as they agree with previous results on which some 

 observations have been made already. 



It will be noticed that none of the four soils used in these 

 experiments had the power of absorbing completely the whole of 

 the ammonia, potash, or phosphoric acid contained in the liquid 

 manure. A certain amount of these constituents always remained 

 in the liquid which was left in contact with soil. As the liquid 

 manure contained a good deal of ammonia and potash, it may be 

 urged that the quantity of soil employed in the experiments in 

 relation to that of the liquid was insufficient for the purpose of 

 complete absorption. But this argument certainly does not hold 

 good in the case of phosphoric acid, and probably not in the case of 

 ammonia or potash. With respect to phosphoric acid, I can speak 

 positively on the subject, for I have filtered through the same soils 

 a very much larger proportion of phosphoric acid, and found 

 that nearly the whole of it was retained by three of the soils. 

 But whether a solution containing much or little phosphoric acid 

 be filtered through a moderately stiff soil, invariably some phos- 

 phoric acid passes into the filtered liquid. Again, if a dilute 

 solution of a soluble phosphate is passed through a soil, it may be 

 ascertained readily that there is phosphoric acid in the filtered 

 liquid. If now a fresh quantity of a solution containing phosphoric 

 acid be shaken with the soil through which the first solution has 

 passed, it will be found that the soil takes up a fresh quantity of 

 phosphoric acid. This circumstance appears to me to prove 

 decidedly that soils have not the power of rendering soluble phos- 

 phates so completely insoluble that these compounds cannot enter 



