948 HOW CROPS FEED. 
acids, whereby bodies result which are no longer soluble 
in water, and which, as such, are probably innutritious to 
plants. These substances are quite slowly decomposed 
when put in contact, especially when heated with alkalies 
or caustic lime in the presence of water. In this decom- 
position ammonia is reproduced. These indifferent nitrog- 
enous matters appear to be analogous to a class of sub- 
stances known to chemists as amides, of which asparagin, 
acrystallizable body obtained from asparagus, young peas, 
etc., and urea and uric acid, the characteristic ingredients 
of urine, are examples. Further account of these matters 
will be given subsequently, p. 276. 
Quantity of Ammonia in Soils,—Formerly the amount 
of ammonia in soils was greatly overestimated, as the re- 
sult of imperfect methods of analysis. In 1846, Krocker, 
at Liebig’s instigation, estimated the nitrogen of 22 soils, 
and Liebig published some ingenious speculations in which 
all this nitrogen was incorrectly assumed to be in the form 
of ammonia. Later, various experimenters have attempt- 
ed to estimate the ammonia of soils. In 1855, the writer 
examined several soils in Liebig’s laboratory. The soils 
were boiled for some hours with water and caustic lime, 
or caustic potash. The ammonia that was set free, distill- 
ed off, and its amount was determined by alkalimetry. 
It was found that however long the distillation was kept 
up, ammonia continued to come over in minute quantity, 
and it was probable that this substance was not simply 
expelled from the soil, but was slowly formed by the ac- 
tion of lime on organic matters, it being well known to 
chemists that many nitrogenous bodies are thus decom- 
posed. The results were as follows: 
Ammonia. 
White sandy loam distilled with caustic lime gave in two Eyp's. | 9.0186 a 
ae “ cs “c 6 ‘ 0.0047 ‘ 
Yellow clay os “os Fe | 0.0051 ** 
66 ‘6 ‘“ sc sc potash 6 ‘“ one “ 0.00% ** 
Black garden soil ¥ 2s * . lime.<*.' * ee | o.09s3 
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