250 HOW CROPS FEED. 
Azotometer. (Chemisches Centralblatt, 1860, pp. 243 and 
534.) 
By this method, which gives accurate results when ap- 
plied to known quantities of ammonia-salts, Knop and 
‘Wolff obtained the following results: 
Ammonia in dry soil. 
Very light sandy soil from birch forest............ 0.00077° |, 
Rich lime soil from beech forest.............0e005 0.00087 
_ Bandy loam, forest sOil....... cee cece cece eee eee «0.00012 
HorestisOil sc va wists casita saad owuiyece oanaiecgee sare aon 0.00080 
Meadow soil, red sandy loam..............00eeeee 0.00027 
AVETAG Gs iiacdis ¢ieisterd syoeiersinctars nie 0.00056 
The rich alluvial soils from tropical America are ten or 
more times richer in ready-formed ammonia than those of 
Saxony. These figures show then that the substance in 
question is very variable as a constituent of the soil, and 
that in the ordinary or poorer classes of unmanured soils 
its percentage is scarcely greater than in the atmospheric 
waters. 
The Quantity of Ammonia fluctuates, — Boussingault 
has further demonstrated by analysis what we have insist- 
ed upon already in this chapter, viz., that the quantity of 
ammonia is liable to fluctuations, He estimated ammonia 
in garden soil on the 4th of March, 1860, and then, moist- 
ening two samples of the same soil with pure water, ex- 
amined them at the termination of one and two months 
respectively. He found, | 
March 4th, 0.009° |, of ammonia. 
April “ 0.014“ “ « 
May (79 0.019 co 66 T5 
The simple standing of the moistened soil for two 
months sufficed in this case to double the content of am- 
monia. 
The quantitative fluctuations of this constituent of the 
soil has been studied further both by Boussingault and 
by Knop and Wolff The latter in seeking to answer the 
