36 



CALCAREOUS MANURES— THEORY 



earth be present in a soil thus analyzed, the muriatic acid will take up a 

 small quantity of aluminous earth, which will be precipitated by the car-j 

 bonate of potash, and without further investigation, would be considered 

 as so much calcareous earth. And if any compounds of lime and vegeta- 

 ble acids are present, (which for reasons hereafter to be stated, I believe to 

 be not uncommon in soils,) some portion of them may bfe dissolved, and 

 appear in the result as carbonate of lime, though not an atom of that sub- 

 stance was in the soil. Thus, every soil examined by this method of solu- 

 tion and precipitation will yield some small result of what would appear as 

 carbonate of lime, though actually destitute of such an ingredient. The 

 inaccuracies of this method were no doubt known (though passed over 

 without notice) by Davy, and other men of science who have recommended 

 its use; but as they considered calcareous earth merely as one of the 

 earthy ingredients of soil, operating mechanically, (as do sand and clay,) 

 on the texture of the soil, they would scarcely suppose that a difference of 

 a grain or two could materially affect the practical value of an analysis, or 

 the character of the soil under examination.* 



The pneumatic apparatus proposed by Davy, as another means for 

 showing the proportion of calcareous earth in soils, is liable to none of 

 these objections ; and when some other causes of error peculiar to this 

 method, are known and guarded against, its accuracy is almost perfect, in 

 ascertaining the quantity of calcareous earth— to which substance alone 

 its use is limited. The following representation and description will make 

 the operation quite clear. 



"A, B, C, D, represent the different parts of this apparatus, A represents the bottle 

 for receiving the soil. B the bottle containing the acid, Ininished with a stop-cocli. 

 C the tube connected with a flaccid bladder. D the graduated measure. E tlie bottle 

 for containing the bladder. When this instrument is used, a given quantity of soil is 

 introduced into A. B is filled with muriatic acid diluted with an equal quantity of water ; 

 and the stop-cock being closed, is connected with the upper orifice of A, which is 



* " Chalks, calcareous marls, or powdered limestone, act. merely by forming a xisefiil 

 earthy ingredient in the soil, and their efficacy is proportioned to the deficiency of calca- 

 reous matter, which in larger or smaller quantities seems to be an essential ingredient of 

 all fertile soils; necessary perhaps to their proper texture, and as an ingredient in the 

 organs of plants." [Davy's Agr. Chem. page 21— and further on he says] " Chalk and 

 marl or carbonate of lime only improve the texture of a soily or its relation to absorption ; 

 it acts merely as one of its earthy ingredients." 



