ANALYSIS. 



ANALYSIS. 



rate the particles, but not to grind them : any | 2-3 ; silicious sand from 2-5 to 2-7 ; mixed 

 small stones above the size of a pea must be j soils have specific gravities varying accordin 

 taken out. It' these form a considerable part to the proportions of their component nart^ 



part o tne proportions 01 meir component parts, 

 of the soil, their proportion must be ascertained i Those in which clay, chalk, and humus abound, 

 by weight; their nature and quality may be j and which are generally the most fertile, are 

 afterwards examined : this being a very simple the lightest. The sandy soils are heavier, and 



the more so if they contain oxides of iron, or 

 of other metals ; and it is well known that the 

 ferruginous sands are the most barren. The 



operation, and obvious to the sight, need not 

 be described. Where the stones and pebbles 

 are evidently accidental, they may be over- 



looked, as having little influence on the ferti- 

 lity : the dry earth, cleared from stones, should 

 be accurately weighed ; and it is convenient to 

 take some determined quantity of grains, as 

 1000, 500, or 250, according to the accuracy 

 of the instruments at hand. This portion 

 should be put into a shallow earthen or metal 

 vessel, and heated over the fire, or a lamp, for 

 about ten minutes, stirring it with a chip of 

 dry wood; the heat should not be so great as 

 to discolour the wood. It may then be allowed 

 to cool, and be weighed again ; the loss of 

 weight indicates the water which remained 

 uncombined after the soil appeared quite dry. 

 Thi.s is the first thing to be noted. The power 

 of retaining water without any external appear- 

 ance of moisture is greatest in humus (a mo- 

 dern term for very finely divided organic 

 matter), next in clay, both of which readily 

 absorb it from the atmosphere; carbonate of 

 lime does so in a less degree, and silicious 

 sand least of all. This moi.-turi; occupies the 

 pores of the soil, and is very different from the 

 water, which is combined with clay as a part 

 of its substance, and to which it owes its 

 ductility; for when this last is expelled by a 

 great heat, the clay loses its quality, and ap- 

 proaches to the nature of sand. Pounded brick 

 will not bind with water, and porcelain reduced 

 to fine powder has all the properties of silicious 

 sand in the soil. The finer the division of the 

 particles of the soil, the greater will be its 

 of absorbing and retaining water ; but 

 in a soil where clay greatly predominates, the 

 lumps sometimes become so hard and baked 

 by tne sun that the moisture cannot penetrate ; 

 and in this case the power of absorption is 

 much diminished. Hence loams in which 

 there is a good proportion of humus have a 

 greater power of absorption than the pure 

 earths. Taking all circumstances into consi- 

 deration, it will be found that the soils which 

 most readily absorb moisture are also the most 

 fertile, and therefore it is important to ascer- 

 tain their power of absorption. This can be 

 found by comparison. Equal portions of dif- 

 ferent soils, dried as before, are placed in the 

 opposite scales of a good balance, and left ex- 

 posed for some time to a moist atmosphere ; 

 that which preponderates has the greatest 

 power of absorption ; the degree is measured 

 by the difference of the acquired weights. 

 Another important circumstance is the specific 

 gravity of a soil. The different earths have 

 very different specific gravities; and humus 

 being lighter than any mineral earth, the 

 lightness of the soil is a sure indication of its 

 richness, excepting where this lightness is 

 occasioned by an excess of undecomposed 

 vegetable matter, or peat. Humus, when 

 nearly pure, has specific gravity varying from 

 1-2 to 1-5; fine porcelain clay, 2; chalk, about 



common expression of light, when applied to a 

 sandy soil, has no reference to its specific gra- 

 vity, 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 (p. 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 hold- 

 ing 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 poise 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 

 silicious 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 .... 



Silicious sand 



Calcareous sand - 



Carbonate of lime 



Humus - 



had a specific gravity of 2-332. 

 A good loam, consisting of 

 Clay - --- 

 Silicious sand 

 Calcareous sand - 

 Carbonate of lime - 

 Humus - - - 



had a specific gravity of 2-401. 

 A poorer soil, of which the component rarte 



were, 



Silicious sand - 64-0 



Clay 32-3 



Calcareous sand - - *'* 



Carbonate of lime - - - 1'* 

 Humus _.-- 



had a specific gravity of 2-526. 



These examples suffice to show that the spe- 

 cific gravity of a soil is some tolerable ind^a- 



87 



52-4 

 36-5 

 1-8 

 2-0 

 7-3 



51-S 



427 



0-4 



2-3 



3-4 



