30 THE ATMOSPHERE. II. 



milligrams of ammonia in 100 cubic metres of air, in winter ; 

 and 2*09 milligrams per 100 cubic metres in summer. The 

 maximum observed was 9 milligrams per 100 cubic metres, 

 while on several occasions no ammonia was present. Accord- 

 ing to Heinrich* air contains the greatest amount of ammonia 

 in June, the least in February. He found three times as 

 much in the summer months as in the winter, while spring 

 and autumn gave intermediate values. 



Ammonia, in common with nitric acid and suspended 

 matter, is found in rain-water. 



" According to Levy rain (unlike air) in summer contains 

 least and in winter most ammonia. This may be due to the 

 solubility of ammonia being greater in cold than in hot water. 

 At Montsourisf the following were the mean amounts of 

 ammonia per litre, rainfall (in m.m.), and quantity of nitrogen 

 (ammoniacal) falling upon each square metre in each of the 

 following years : 



1875-76 



1876-77 



1877-78 



1878-79 



This, being practically town rain, is richer in ammonia than 

 rain falling in country places. As the average of 16 years' 

 observations Levy gives 2-2pts. per million of ammonia = 

 l'82pts. N. per million in the rain at Montsouris. (See also 

 analyses of rain-water p. 31.) 



Bunsen observed that at the commencement of a shower the 

 rain contained 3'7 milligrams of ammonia per litre, while at 

 the end only -64 milligrams were present. 



Nitric Acid, or some compound of nitrogen and oxygen, is 

 also found in air, in which it probably exists in the form of 

 nitrate and nitrite of ammonia, and according to Miintz and 

 Aubinj these in the state of finely-divided solid. The authors 

 quoted state that thunderstorms (and the accompanying for- 

 mation of nitrates) are confined to the lower portion of the 



* J.C.S. 1898, abst. ii. 3, 114. f Compt. Rend. 91, 94. { Compt. Rend. 95, 919. 



