330 HOW CROPS FEED. 
On the other hand, all carbonates, sulphates, and phos- 
phates, are completely dissolved, while the zeolites and. 
serpentine are decomposed, their alkalies, lime, etc., enter- 
ing into solution, and the silica they contain separating, for 
the most part, as gelatinous hydrate. 
According to the nature of the soil, and the concentra- 
tion of the reagent, hydrochloric acid, the solvent usually 
employed, takes up from two to fifteen or more per cent. 
Very dilute acids remove from the soil the bases, lime, 
magnesia, potash, and soda, in scarcely greater quantity 
than they are united with chlorine, and with sulphuric, 
phosphoric, carbonic, and nitric acids. Treatment with 
stronger acids takes up the bases above mentioned, par- 
ticularly lime and magnesia, in greater proportion than 
the acids specified. We find that, by the stronger acids, 
silica is displaced from combination (and may be taken 
up by boiling the soil with solution of soda after treat- 
ment with the acid). It hence follows that silicates, such 
as are decomposable by acids, (zeolites) exist in the soil, 
although we cannot recognize them directly by inspec- 
tion even with the help of the microscope. To this point 
we shall subsequently recur. 
§ 4, 
PORTION OF SOIL INSOLUBLE IN ACIDS. 
When a soil has been boiled with concentrated hydro- 
chloric acid for some time, or until this solvent exerts no 
further action, there may remain quartz, feldspar, mica, 
hornblende, augite, and kaolinite (clay), together with 
other similar silicates, which, in many cases, are ingredients 
of the soil. Treatment with concentrated sulphuric acid ~ 
at very high temperatures (Mitscherlich), or syrupy phos- 
phoric acid (A. Miiller), decomposes all these minerals, 
quartz alone excepted. By making, therefore, in the first 
