THE ATMOSPHERE. 193 



and its influence on the growth of plants is maintained by 

 Liebig. Future analysis may determine the presence and 

 influence of other matters, which at present elude our analytic 

 methods, or whose presence is only suspected. 



Marchand found, as the mean of 150 experiments, that 

 10,000 volumes of air contain 3.1 of carbonic acid. Kemp 

 found that 24,840 cubic inches of air yielded 1.8 milligrammes 

 of ammonia. Grseger and Horsford have also found ammonia. 



The discrepancies in the experiments of Graeger, Avhich gave 

 0.323 grm. ammonia = 0.988 carbonate, and those of Dr. 

 Kemp, determining 3.68 caustic = 10.37 carbonate of ammonia 

 in 1,000,000 grm. of the atmosphere, induced Fresenius to 

 make some essays with a view to the correct decision of the 

 matter. His apparatus consisted of two gasometers, of nearly 

 2 galls, capacity each, with a collecting apparatus of two 

 flasks, containing 1 pt. muriatic acid of 1.12 and 20 pts. water. 

 The passage of the air was continued, day and night without 

 intermission, for six weeks. The results obtained were .089 

 ammonia = .283 carbonate during the day, and .169 ammonia 

 = .474 carbonate during the night, in every 1,000,000 grm. 



3. 3Iineral Manures. — That mineral matters in the soil 

 exert an important influence on plants is generally admitted, 

 but which substances are most influential and how far they are 

 beneficial have not been determined. On this head, we call 

 attention to the investigations of G. Magnus, of Berlin. 



Magnus made a series of careful experiments, during 1849, 

 on the growth of plants (barley having been selected), from 

 which he drew the following conclusions : 



1. When mineral matters are not present, the barley attains 

 only the height of 5 inches, and then dies. 



2. When a small quantity of mineral matter (difierent saltsj 

 is present, perfect development takes place. 



3. If somewhat more mineral matter is present, the plant 

 either grows in a stunted form or is not developed at all. 



4. In feldspar alone, barley attains complete development 

 and produces seeds. 



R 13 



