15G ON THE RATIONALE OF CERTAIN MANURES 



Ly applying- g-ypsiim already formed ; but, then, it is to be 

 considered that sulphuric acid in the very act of producing" 

 this salt disintegrates the soil, releases its component parts 

 from the cohesive attraction which before acted as an anta- 

 gonist force to chemical affinity, and also, above all, converts 

 the minute quantity of phosphate of lime present in most 

 soils into a superphosphate, thus rendering- it more soluble. 



If we put tog-ether all these several advantages, it may be 

 conceived that a dressing- of sulphuric acid will often suc- 

 ceed better than one of g-ypsum would do, the superior cost 

 of the article being- compensated by the benefit accruing- 

 from its power of converting- the dormant principles of the 

 soil into those which are active, or directly available for its 

 purposes. 



Gypmm. — In alluding- to the subject of g-ypsum, I cannot 

 refrain from pointing- out that it affords a striking- illustra- 

 tion of the great uncertainty which still prevails with re- 

 spect to the theoretical principles by which the practice of 

 agriculture is at present g-uided. 



We have here four distinguished authorities in the science 

 of agricultiu'e, namely, Sir Humphry Davy, Baron Liebig, 

 Monsieiu- Boussingault, and Professor Johnston, of Durham, 

 expressing as many distinct views with respect to the opera- 

 tion of this agent as a maniu-e — Sir Humphr}' regarding- it 

 as advantageous by reason of both its constituents, that is, 

 acting as sulphate of lime; Baron Liebig directly by neither 

 one, but indirectly as fixing- the ammonia of the atmosphere; 

 Boussingault attributing its usefulness to the lime it con- 

 tains, and Professor Johnston chiefl}^ to its sulphuric acid. 



I allude to this discrepancy of opinion rather in order to 

 press upon the minds of agriculturists the importance of in- 

 stituting inquiries for the purpose of ascertaining- more pre- 

 cisely the modus openmcVi of this and other measures, than 

 for the sake of obtruding- any views of my own on the ques- 

 tion more immediately before us — views which have not 

 been tested by any specific train of experiment, and which 

 are therefore the less worthy of being- brought into compe- 

 tition with those of such distinguished philosophers. 



Nevertheless, I may remark, that, of the four theories 

 just mentioned, the one proposed by Boussingaiilt seems to 

 me the most destitute of probability. It offers no explana- 

 tion whatsoever of the peculiar adajitation of gypsum for 

 plants of the leguminous order, nor for the preference which 

 practical men assign to its use over that of lime, where the 



