190 E. W. Hilgard— Objects and Interpretation of Soil Analyses. 
investigation of its relation to the productiveness of soils, to a 
definite conclusion. There can be no reasonable doubt that 
what 7s extracted by Grandeau’s ammonia water is at the com- 
mand of the solvents employed by plants; the only question is, 
to what extent plants can readily go beyond. This of course 
requires extended culture experiments, on a great variety of 
soils. 
The determination of the phosphoric acid and silica in the 
residues from the ignition of Grandeau’s extracts have already 
furnished most important data concerning the cause of the pro- 
ductiveness of some soils having comparatively a low percent- 
age of phosphates. 
As regards the determinations of nitrogen and its compounds 
in the virgin soils thus far analyzed, I have omitted them in part 
from want of time and proper appliances for these delicate de- 
terminations, and partly from a doubt of their usefulness. The 
constant variation and inter-convertibility of nitrates and am- 
monia-compounds renders their determination at any given 
soil. A full investigation of this subject is, of course, also 
e first question arising in this connection, is naturally, 
whether all soils, having what experience proves to be high 
percentages of plant-food when analyzed by the processes 
above given, show a high degree of productiveness ? on 
ras my experience goes, this question can, for virgin 
soils, be unqualifiedly answered in the affirmative ; provided 
only, that improper physical conditions do not interfere with 
the welfare of the plant. 
ut it does not therefore follow, as was at first supposed, 
that the converse is true, and that low percentages necessarily 
indicate low production. This will be apparent from a simple 
consideration. 
, or even more, of 
coarse sand, thereby reducing the percentages to one-half, or 
