ATMOSPHEiaO Aia aS THE T<OOI> OP PLANTS. 80 



brouglit down per acre in {ho form of ammonia was 9.93G 

 lbs.; that in the ibrm of nitric acid Mas 0.9T4 lbs. The 

 total nitrogen contained in the rain, etc., was accordingly 

 10.91, or, in round numbers, 11 lbs. avoirdupois. The rain-, 

 fall amounted to 488.309 imperial gallons, (Wilda's Cen- 

 tmlhlatt, August, 1866.) 



Relation of Nitric Acid to Ammonia in the Atmos- 

 pliere. — The foregoing results demonstrate that there i8 

 in the aggregate an excess of ammonia over the amount 

 required to form nitiate with the nitric acid. (In nitrate 

 of ammonia (XH^ XO3)? ^^'^ acid and base contain the 

 same quantity of nitrogen.) We are hence justified in 

 assuming that the acid in question commonly occurs as ni- 

 trate of ammonia * in the atmosphere. 



At times, however, the nitric acid may preponderate. 

 One instance is on record (Journal de Pharmacie^ Apr., 

 1845) of the presence of free nitric acid in hail, which fell 

 at Nismes, in June, 1842. This hail is said to have been 

 perceptibly sour to the taste. 



Cloez ( Conipt. Mendus, lii, 527) found traces of free 

 nitric acid in air taken 3 feet above the ground, especially 

 at the beginning and end of winter. 



The same must have been true in the cases already giv- 

 en, in which exception;dly large quantities of nitric acid 

 were found, in the examinations made by Boussingault and 

 the Prussian chemists. 



The nitrate of ammonia which exists in the atmosphere 

 - d'Hibtless held there in a state of mechanical suspension. 

 it is dissolved in the falling rains, and when once brought 

 to the surface of the soil, cannot again find its way into 

 the air by volatilization, as carbonate of ammonia does, 

 but is permanently removed from the atmospheie, and 



* In evaporating large quantifies of rain-water to dryness, there are often found 

 In the residue nitrates of lime and 6oda. In these cases the lime and soda come 

 from dust suspended in the air. 



