256 HOW CROPS FEED. 
further researches must decide. The quantities that ac- 
cumulated in this experiment are seen to be very consider- 
able, when we remember that experience has shown that 
200 Ibs. per acre of the nitrates of potash or soda isa 
large dressing upon grain or grass. Had the earth been 
exposed to occasional rain, its analysis would have indi- 
cated a much less percentage of nitrates, because the salt 
would have been washed down far into, and, perhaps, 
out of, the soil but no less, probably even somewhat 
more, would have been actually formed. In August, 1856, 
Boussingault examined earth from the same garden after 14 
days of hot, dry weather. He found the nitrates equal to 
911 Ibs. of nitrate of potash per acre taken to the depth of 
one foot. From the 9th to the 29th of August it rained 
daily at Liebfrauenberg, more than two inches of water 
falling during this time. When the rain ceased, the soil 
contained but 38 lbs. per acre. In September, rain fell 15 
times, and to the amount of four inches. On the 10th of 
October, after a fortnight of hot, windy weather, the gar- 
den had become so dry as to need watering. On being 
then analyzed, the soil was found to contain nitrates equiv- 
alent to no less than 1,290 Ibs. of nitrate of potash per 
acre to the depth of one foot. This soil, be it remembered, 
was porous and sandy, and had been very heavily manur- 
ed with well-rotted compost for several centuries, 
Boussingault has examined more than sixty soils of ev- 
ery variety, and in every case but one found an apprecia- 
ble quantity of nitrates. Knop has also estimated nitric 
acid in several soils ( Versuchs St., V, 148). Nitrates are 
almost invariably found in all well and river waters, and 
in quantities larger than exist in rain. We may hence as- 
sume that nitrification is a process universal to all soils, 
and that nitrates are normal, though, for the reasons stat- 
ed, very variable ingredients of cultivated earth. 
The Sources of the Nitric Acid which is formed within 
the Soil.—Nitric acid is produced—a, from ammonia, 
