ACID SOLUTION OF THE SOIL. 329 



lime, magnesia, and soda, it is difficult or impossible to 

 wash out completely from a soil of good c|.uality. 



Very poor soils may be deficient in soluble forms of 

 any or several of the aoovc ingredients, and therefore 

 readily admit of nearly complete extraction by a small 

 amount of water. 



Certain soils contain soluble salts of iron and alumina 

 (sulphates and humates) in considerable quantity, and 

 are for that reason unproductive. Such are many marsh 

 lands, as well as upland soils containing bisulphide of iron 

 (iron pyrites), of the kind that readily oxidizes to sulphate 

 of protoxide of iron (copperas). 



SOLUTION OF THE SOIL IN STRONG ACIDS. 



The strong acids, hydrochloric (muriatic), nitric, and 

 sulphui-ic, by virtue of their vigorous affinities, readily 

 remove from the soil a considerable quantity of all its 

 mineral ingredients. The quantity thus taken up is 

 greatly more than can be dissolved in water, and is, in 

 general, the gieater, the more fertile the soil. Exceptions 

 are soils consisting largely of carbonate of lime (chalk 

 soils), or compounds of iron (ochreous soils). The differ- 

 ent acids above named exercise very imlike solvent effects 

 according to their concentration, the time of their action, 

 the temperature at which they are applied, and the chemi- 

 cal nature and state of division of the soil. 



The deportment of the minerals which chiefly constitute 

 the soil towards these acids will enable us to under- 

 stand their action ujDon the soil itself Of these minerals 

 quartz, feldspar, mica, hornblende, augite, talc, steatite, 

 kaolinite, chrysolite, and chlorite, when not altered by 

 weathering, nearly or altogether resist the action of even 

 hot and moderately strong hydrochloric and nitric acids. 



