Essay on the Analysis of Soils. 



49 



abound, and which are generally the most fertile, are the 

 lightest. The sandy soils are heavier, and the more so if they 

 contain oxydes of iron or of other metals ; and it is well known 

 that the ferruginous sands are the most barren. The common 

 expression of light, when applied to a sandy soil, has no reference 

 to its specific gravity, but merely to the force required to plough it. 

 No carrier would say that a loose sandy road was a light one. 



The easiest and readiest method of determining the specific 

 gravity of earth, or any substance which is of a loose texture, is 

 that described by Dr. Ure in his Philosophy of Manufactures, 

 (page 97), as employed by him to ascertain the specific gravities 

 of cotton, wool, silk, and flax. It is as follows : — Take a narrow- 

 necked phial capable of holding four or five ounces of water ; 

 mark a line round the middle of the neck with the point of a 

 diamond or a file ; fill the phial up to the mark with river or rain 

 water, and poize it with sand or any other substance in a scale ; 

 then put 1000 grains weight in the same scale with the phial, and 

 pour out water till the equilibrium is restored. In the vacant 

 space, which is evidently equal to the bulk of 1000 grains of 

 water, introduce the soil till the water rises to the mark in the 

 neck. Then put into the opposite scale grain weights sufficient to 

 restore the equilibrium. The number of grains required for this 

 purpose will denote the specific gravity of the soil compared to 

 water as 1000. Suppose, for example, that siliceous sand, which 

 is 2.7 times denser than water, is poured into the vacant space, 

 it will require 2.700 grains to fill the space occupied by the 

 1000 grains of water; and thus we have the specific gravity 

 without any calculation. If instead of 1000 grains, we use only 

 500, or 250, the result will be the same, if we multiply the grains 

 in the other scale by 2 or 4. 



We will give a few examples of soils of which the specific 

 gravity has been carefully determined. 



A rich garden soil, which contained per cent.. 



Clay 52.4 



Siliceous Sand . . . 36.5 



Calcareous Sand ... 1.8 



Carbonate of Lime . . 2.0 



Humus 7.3 



had a specific gravity of 2.332. 



A good loam consisting of 



Clay 51.2 



Siliceous Sand . . . 42.7 

 Calcareous Sand . . . 0.4 

 Carbonate of Lime . . 2 3 



Humus 3.4 



had a specific gravity of 2.401. 



VOL. I. E 



