REPORT OF THE CHEMIST. 97 
and phosphoric acid were absorbed by all soils to a considerable extent. 
Way also showed that cultivated soils not only absorb free alkalies and 
acids, but have likewise the power of separating ammonia, potash, and 
other bases from preéxisting combinations. He operated on single 
solutions, and it might be objected that no inference could be safely 
drawn as to-what an actual soil might do if the conditions were varied, 
so that, instead of one solution, several, or a mixture of several salts 
dissolved, were to be presented to that soil; and as this is what actually 
occurs, it became unecessary to interrogate nature by experiment on this 
point. Voelcker’s experiments on the action of soils on liquid manure, 
and on sewage percolated through them, showed how very inferior sandy 
soils were to calcareous clay soils in their power of retaining ammonia 
and potash. If the manure added contained any lime, much more of it 
was removed by the sandy soil than by,the clay; and as regards com- 
mon salt, there seemed no special attraction exerted by any soil, how- 
soever different might be its composition, the chloride of sodium 
diffusing itself out from every soil in the rainfall. From these and 
similar experiments, it is rendered evident that there is an inherent 
power in soils which results in storing up mineral food, and that this 
power is not contined to one particular kind of fertilizing matter, but 
applies to them all, and is exhibited in a manner modified by the special 
constitution of the soil. Another very important fact deducible from 
Voelcker’s experiment is, that this absorbing and detaining power of 
soils is not exerted on very weak solutions. Neither the ammonia, 
potash, phosphoric acid, nor other fertilizing matter contained in a 
solution, were ever completely absorbed by any soil, however weak or 
concentrated the solutions were which were filtered through the soil. 
“Indeed,” says Voelcker, “ if the solution of saline matter brought into 
contact with the soil be very dilute, scarcely any absorption of ammonia, 
potash, or phosphoric acid takes place.” This latter statement is very 
important, as it shows that sewage of towns is of no value when very 
dilute, (and it is almost always too dilute,) since the soil, though possess- 
ing highly absorbent powers, has not the power of overcoming the 
affinity of the water of the solution, and hence it withdraws none of 
the fertilizing matter of the sewage. Cne of the uses of calcareors 
marls, therefore, upon sandy or pure clay soils, is to increase the power 
‘of such a soil to absorb ammonia and potash. Carbonate of lime 
absorbs six times as much ammoniacal salt as stiff clay. If it were not 
for this retentive power, carbonate of ammonia, when present in the soil 
aud carried down by the moisture in the wet season, would, wheu the 
season is dry and the solar heat strong, be carried to the surface of the 
soil and evaporated at once. It is in this way that gypsum (sulphate of 
lime) acts, hindering by its presence the dispersion of the greater part 
of the ammonia. These soluble substances are constantly rising and 
falling in the soil, according as it is wet or dry, cold or heated. These 
matters descend during rain or in winter, and rise during the warmth 
of summer, when the evaporation is greatest.and when the plants need 
more moisture and food. The ascension of these matters varies thus 
every month, and thus the analysis of a soil at one period of the year 
does not exactly represent its composition at another; it is variable at 
different times, and, therefore, no exact idea of the chemical or physical 
properties of a soil can be obtained by a single analysis, no matter how 
accurately conducted. 
ye 
