290 AMMONIA AND NITRIC ACID. 



nitrogen), and 34 Idlogrammes (=751bs.) of nitric acid 

 (=5 kilo. =11 lbs. nitrogen) ; altogether, therefore, 

 27 kilo, or 54 ZoUv. lbs. (=59 lbs. Eng.) of nitrogen. 



For an English acre this makes 21-9 ZoUv. lbs. 

 (=24 lbs. Eng.), and for a Saxon acre 30 Zollv. lbs. 

 These numbers nearly coincide with the observations of 

 Boussinganlt and Knop. 



The yearly average quantity of rain falling in various 

 districts, according to the position and elevation of the 

 locahties, is very unequal ; and investigations have shown 

 that the amount of ammonia and nitric acid contained in 

 rain-water bears an inverse proportion to the quantity of 

 rain. In districts where the rain falls more seldom or 

 less in quantity, the water is richer in these constituents 

 than in more ramy districts. According to Boussinganlt, 

 dew is richest in ammonia ; according to Knop, not 

 richer than rain-water. (See his valuable memoir in the 

 8 hefte der ' Landw. Versuchstat. in Sachsen.') But plants 

 receive ammonia and nitric acid not merely by means of 

 rain-water derived from the ground and in dew, but also 

 du-ectly from the atmosphere. The experiments of 

 Boussinganlt (' Annal. de Chem. et de Phys.,' 3 ser. t. liii.) 

 leave no doubt whatever with regard to the constant 

 presence of ammonia in the air. In a kilogi^amme of 

 the following substances heated to redness, he found 

 these .quantities of ammonia, after three days' exposure 

 to the air upon porcelain plates : — 



In 1 kilo, quartz-sand . .0*60 milligr. ammonia 

 „ 1 ,, bone-ash . . 0-47 „ 



,, 1 „ charcoal . . . 2*9 „ 



Although we can estimate with tolerable certainty the 

 quantity of ammonia and nitric acid which a field 

 annually receives in rain-water, yet the determination 

 of the same in the dew which moistens plants is not 

 practicable. Just as httle can we discover how much 



