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Poicer of Soils to ahsorh Manure. 



to teacti their true cause, and, as was then explained, it was left 

 for further efforts to carry out this all important branch of the 

 inquiry. I may briefly state here, that in the time that has 

 elapsed since the publication of the above-mentioned paper, I 

 have paid unremitting attention to the prosecution of this 

 investigation, and that the result has been as successful as my 

 most sanguine expectations would have anticipated ; I am now 

 in a position to show, with every certainty, the efficient cause of 

 the singular power which soils, especially those of good quality, 

 possess of retaining the manure that is applied to them, and even 

 of acquiring fertility without the direct addition of such manure ; 

 and although the present account, like the preceding one, does not, 

 by a great deal, close the inquiry or exhaust the subject, a con- 

 fident hope is entertained that the reader will find in it much to 

 interest him, and that he will recognise the very material progress 

 which has been made since the last occasion on which his atten- 

 tion was enlisted in its favour. 



To save the necessity of reference to the previous paper, and 

 to present the subject in as connected a form as possible, I shall 

 briefly recapitulate the principal results which were there 

 recorded. 



In the first place, then, it was found that ordinary soils pos- 

 sessed the power of separating from solution in water the different 

 earthy and alkaline substances presented to them in manure ; 

 thus, when solutions of salts of ammonia, of potash, magnesia, 

 &e., were made to filter slowly through a bed of dry soil, 5 or 

 6 inches deep, arranged in a flower-pot or other suitable vessel, 

 it was observed that the liquid which first ran through no longer 

 contained any of the ammonia or other salt employed. The 

 solution might have been at the commencement of the experi- 

 ment sufficiently strong to make the detection of the ammonia or 

 the potash, by the proper tests, a matter of great ease, but after 

 filtration through the soil it was no longer to be found ; in point 

 of fact the soil had, in some form or other, retained the alkaline 

 substance, whilst the water in which it had previously been dis- 

 solved was passing through. 



But further, this power of the soil was found not to extend to 

 the whole salt of ammonia or potash, but only to the alkali itself. 

 If, for instance, sulphate of ammonia were the compound used in 

 the experiments, the ammonia would be removed from solution, 

 but the filtered liquid would contain sulphuric acid in abundance 

 — not in the free or uncombined form, but united to lime ; 

 instead of sulphate of ammonia we should find, after the experi- 

 ment, sulphate of lime in the solution; and this result was 

 ^ obtained whatever the acid of the salt experimented on might be. 

 When the sulphates of ammonia, potash, magnesia, &c. were 



