THE CHEMISTRY OF THE FARM. 409 



constituents to plants, but we must know the state in which they exist. 

 Hence a complete analysis of a soil should inform us as to the proportion 

 of substances voluble in water, soluble in adds, and insol 9. A 



soil, from which all pebbles and considerable fragments have been sifted, 

 should be insoluble in acids, and therefore unavailable for present use, 

 is itself a striking fact. Equally strange does it appear that '1 to '3 per 

 cent, should represent the amount we may suppose to be readily available 

 for solution. But although the percentage is small relatively, it is very 

 considerable positively, amounting to from one to three tons per acre of 

 ten inches in depth. 



The insoluble portion of soils must not be looked upon as useless. Not 

 only is it the medium by which nourishment finds its way to the roots of 

 plants, but owing to the continued action of the forces already noticed, a 

 further disintegration is constantly taking place a weathering action 

 whereby fresh portions or particles of insoluble matter pass over into a 

 soluble and available condition. The entire mass of soil may then be 

 divided into ACTIVE and DORMANT constituents, the former class being 

 constantly, although slowly, recruited from the latter. A soil which has 

 borne successive crops of grain becomes exhausted of the active or imme- 

 diately available ash constituents. A field exhausted in this sense, if 

 allowed a period of rest, will be found to have regained its fertility, simply 

 because fresh portions of mineral matter have been digested and reduced 

 to a soluble condition. These considerations, therefore, show clearly that 

 the large proportion of material in a soil, insoluble in acids, may be re- 

 garded as a m/igazine of mineral plant food, which will become available 

 in tin- distant futuiv. 



Tin- actual percentage composition of the soil is shown in the following 

 analyses made by various eminent chemists. It is but seldom that a 

 thorough analysis is made of all the divisions, soluble in water, solul-le 

 in acids, ami insnluhlf in acids. In the following examples the insoluble 

 matter is lumprd t..^, tli. r as insoluble silicious matter. The table shows 



composition <!' a I'-i-tilr alluvial soil from near the /uidri /re. in 1 ! 

 land, analysed l,y Daumhauer. 



