440 3 E. W. Hilgard—Soil Analyses and their Utility. 
tity varies continually in the soil, as it does in the atmosphere; 
its chief absorbers in the soil are “humus” and clay. Where 
these prevail largely, ammonia can scarcely be deficient as a 
nutritive ingredient to an injurious extent; albeit, more might 
doubtless be beneficially added. Moreover, the characteristic 
effects of ammonia on vegetation are sufficiently obvious (in 
“running to weed”) to render its determination in virgin soils, 
laborious and even uncertain as it is, a matter of comparatively 
little practical consequence, however great might be its theo- 
retical interest. ‘ 
s for the determination of the degree of oxidation of iron, 
I confess I fail to see its practical bearing. When ferric oxide 
is present, plants surely can have no difficulty in reducing the 
modicum they need to a soluble condition. When ferrous oxide 
exists to any great extent, it indicates a want of drainage, and 
manifests itself both in the color of the soil and in the poison- 
ous effect on vegetation. But farmers surely do not need the 
aid of chemical analysis to tell them that their soil needs 
drainage and aération! A determination made to-day would 
be of no value to-morrow, if the soil had been plowed in the 
interval. 
Finally, Dr. Peter does determine chlorine, in the treatment of 
i n int 
shows, so little likely to be deficient in the soil, that 1 
omission would not be a serious practical objection. 
A much graver defect is the failure to determine separately 
the organic matter (“humus”) and the chemically combined 
minations in question can be effected even approxima” 
That they should form part of every soil analysis, 1s obvious, 
I have attempted to obtain a reliable scale of the different 
d s of “heaviness” of soils, from the determination of 2 
maximum absorption of h pic moisture at ordinary to 
peratures. about - a 
+21°, the amount of aqueous vapor absorbed by a thin layet 
of soil exposed to yh 
