ATMOSPHERE IN ITS RELATIONS TO VEGETATION. 163 



on land the reverse is the case, esiDecially inthe neighborhood of vegetation, 

 as recently shown by Truchot. Plants continue to produce carbonic acid 

 in the night as in the day, but in daylight the decomposition of carbonic 

 acid is so great that none is evolved, while in the night evolution takes 

 place. According to Truchot the proj)ortion of carbonic acid in the air 

 diminishes with an increase of altitude, and is less on mountains than in the 

 valleys. This is probably the case, as the carbonic acid of the air is sup- 

 plied by exhalations from the earth. 



Truchot has also made some experiments- on the influence of altitude on 

 the amount of ammonia present in the atmosphere. The greatest altitude 

 employed for observation was the summit of the Pic de Sancy, about 6000 

 feet above the sea. There appeared to be a distinct increase in the amount 

 of ammonia at considerable altitudes, and the quantity was apparently 

 greater in foggy than in clear weather. The largest quantity of ammonia 

 found was 1 lb. in about 107,289 cubic yards, and the smallest amount 1 lb. 

 in 640,262 cubic yards of air. 



The ammonia in the' air is probably derived entirely from exhalations 

 from the earth, though Schlesing believes that a portion of it emanates from 

 the ocean. The nitrates washed into the sea in vast quantities by rivers 

 are, in his opinion, converted first into food for marine plants, and on the 

 death of these plants, or of the animals feeding on them, a part of the nitro- 

 gen is returned to the air as ammonia. 



Of nitrous acid the air has undoubtedly an original source in the electric 

 discharges, silent or otherwise, which are continually occurring. It is well 

 known that nitric acid is produced whenever an electric spark passes 

 through the air, and it was supposed that the ozone produced by the spark 

 was capable of oxidizing nitrogen into nitric acid. This property of ozone 

 if established, was clearly of great importance, as ozone is apparently given 

 off in small quantities by plants in sunshine, and vegetation would thus it- 

 self afford a supply of combined nitrogen. But according to Carius, who 

 has thoroughly investigated the subject, ozone is quite incapable of oxidiz- 

 ing free nitrogen ; it will, however, oxidize ammonia into nitrites and 

 nitrates, and doubtless converts into nitric the nitrous acid produced by 

 electric action. 



Another oxidizing substance present in the atmosphere is peroxide of 

 hydrogen. The conditions under which it occurs have been studied to some 

 extent in Germany, but the results as yet obtained are not very definite. 



The total amout of combined nitrogen which is brought to the soil an- 

 nually in the form of rain was determined some years ago at Eothamsted. 

 Bretschneider more recently has given the results of six years' observations 

 at the experimental station of Ida-Marienhutte where the average rainfall 

 is about 22.5 inches. The quantity of combined nitrogen (ammonia and 

 nitric and nitrous acid) contained in the rain, varied during the six years 

 from 6.32 lbs. to 12.61 lbs. per English acre, the average being 9.94 lbs. As 

 we remarked last month, the fertilizing influence of snow is due to the nitro- 



