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 thaf 

 200 lbs. per acre of the nitrates of potash or soda is a 

 large dressing upon grain or grass. Had tlie earth been 

 exposed to occasional rain, its analysis Avould have indi- 

 cated a much less percentage of nitrates, because the salt 

 woidd have been Avashcd 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 lbs, 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 duiing 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 lbs. 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 tiian 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 jSt., V, 143). Nitrates are 

 almost invariably found in all well and river waters, and 

 in quantities larger thaii exist in rain. "We may hence as- 

 sume that nitrification is a process universal to all soils, 

 and that nitrates are normal, thougli, for the reasons stat- 

 ed, very variable ingredients of cultivated earth. 



The Sources of the IVitric Acid which is formed within 

 the Soilf — Nitric acid is produced — a, from ammonia^ 



