Oa - aee  e- 
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. -.........ceseuee 0.00087 
Sandy loum, forestseil. ... 0.4. 5. svicc. 2s eee eee 0.00012 
Pofest 500). i... on Te. in de Rees 0.00080 
Meadow soil, red sandy Joam.....3,. «02 sss ae 0.00027 
AVerawte. ¢ sits gh3s cee ee 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 oS. Ge ia 
May <4 0.019 ce 66 “ 
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 
