Tije Soil. 
47 
moniacal solution, by evaporation and incineration, is rich in lime, 
that from the precipitated humus contains only a very slight trace 
of it. The ash from both, the ammoniacal solution of humus and 
the humus precipitated from it, is relatively rich in phosphoric acid. 
§ 98. We made an attempt to determine the ash carried into 
solution by the extraction with ammonia. The results were not 
satisfactory. The solutions were all filtered repeatedly, but owing 
to the intense color of the solutions we could not feel assured that 
some of the variations in our results might not have been due to a 
turbidity in the solution. Our results indicated roughly one per 
cent.; this is probably too high, but it suffices to show that a very 
considerable portion of the whole mass of soil is soluble in this 
ammoniacal humus solution. 
§ 99. Authors have insisted upon the value of humus as a 
solvent for the inorganic constituents of plant food in the soil. Free 
ammonia and ammonie salts are probably present in small quanti¬ 
ties, as previously shown, and we have in the humus, dissolved out 
of the soil by a dilute ammonia solution, phosphoric acid, sulfuric 
acid, potash, lime, iron and an abundance of silicic acid, which are 
not only food for the cultivated plants, but also for the micro-organ¬ 
isms which we believe effect the change of the nitrogen in the 
humus into nitric acid, respectively into nitrates, rendering it also 
available food for the plants. This seems an important function to 
attribute to humus, amounting in but few instances to more than 
one and a half per cent, of the soil, and yet it is justified. Our 
method of treatment or extraction does not faithfully represent the 
soil conditions, and therefore exaggerates its importance. This is 
probably less true than it appears to be, for the acids and bases 
forming the salts of the soil are not in the fixed and quiescent con¬ 
dition in which we usually think of them. On the contrary, there 
are certainly as many, and possibly more, changes going on than 
there would be in a mixture of the same salts in simple aqueous 
solution, and we know that there would be many. We have seen 
that there is probably free ammonia and ammoniacal salts in the 
soil, both of which aid the humus in its action by favoring its solu¬ 
tion. The phosphoric acid extracted with the humus was de¬ 
termined at the beginning of the experiment and again after three 
crops had been grown on the plot. The results are shown in the 
following tables of analyses. 
SOME RESULTS OF THREE SEASONS’ WORK. 
§ 100. The plot had received but little cultivation before I 
began my experimentation with it, and was in such bad condition 
that a part of it was so good as useless for any agricultural pur¬ 
pose. That this was not due to any lack of plant food is indicated 
