ACID SOLUTION OF THE SOIL. 329 
lime, magnesia, and soda, it is difficult or impossible to 
wash out completely from a soil of good quality. 
Very poor soils may be deficient in soluble forms of 
any or several of the above 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). 
oe 
SOLUTION OF THE SOIL IN STRONG ACIDS. 
The strong acids, hydrochloric (muriatic), nitric, and 
sulphuric, 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 greater, 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 unlike 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 upon 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, 
