Absorption of Potash by Soils of known Composition. 337 
Accordingly 1000 grains of this pasture land absorbed 6'57 of 
potash. 
Experiment No. 5. — On a Marly Soil. 
The soil employed in this experiment, on analysis, was found 
to contain in 100 parts : 
Moisture 4 - 72 
Organic matter and water of combination .. .. ll - 03 
Oxides of iron 9-98 
Alumina 6 - 06 
Carbonate of lime 12-10 
Sulphate of lime "75 
Magnesia and alkalies 1*43 
Soluble silica (soluble in caustic potash) .. ... .. 17"93 
Insoluble siliceous matter (chiefly clay) 36-00 
100-00 
The experiment was made precisely as before, with the 
following result : — 
Anhydrous Potash. 
Before contact with soil, the solution contained .. 33 - 966 
After 4 days contact 8 - 554 
Potash absorbed by 3500 grains of soil .. 25-412 
1000 grains of this soil accordingly absorbed 7*26 grains of 
anhydrous potash. In this experiment more potash was absorbed 
than by any of the preceding soils, not excepting even the stiff 
clay. It will also be noticed that this marly soil contained a 
large proportion of soluble silica, as well as a considerable 
amount of oxide of iron and alumina. I find that soluble silica 
and the hydrated oxides of iron and alumina possess the power 
of fixing potash in a large proportion, and their presence in a 
well cultivated clay or marly soil affords thus a guarantee for its 
retention of potash. In many stiff clays, however, that have 
never been pxposed to the ameliorating influence of the atmo- 
sphere, the oxides of iron and alumina, as well as silica, occur in 
a state in which they are not readily acted upon even by powerful 
chemical re-agents, and in this condition we have good grounds 
for believing they do not possess the power of absorbing potash 
or ammonia in any marked degree. Good and deep cultivation, 
by facilitating the action both of air and water, not only unlocks 
the mineral treasures already stored in the soil, but also brings 
the land into a mechanical and chemical condition, which enables 
it to retain the fertility imparted to it by natural or artificial 
manures. 
