AGRICULTURAL CHEMISTRY. 147 



If into a limited volume of several gases be placed a body in the 

 solid or liquid form, which is capable of uniting with chemically, or 

 otherwise destroying the gaseous condition of one of the gases, it will 

 at once absorb those particles of this gas which lie in its immediate 

 vicinity and thus disturb the osmotic equilibrium of the remaining 

 mixture. This equilibrium is at once restored by diffusion of a por- 

 tion of the unabsorbed gas into the space that has been deprived of 

 it and thus the absorption and the diffusion keep pace with each other 

 until all the absorbable air is removed from the gaseous mixture and 

 condensed or fixed in the absorbent. 



In this manner a portion of the atmosphere enclosed in a large 

 glass vessel may be perfectly freed from watery vapor and carbonic 

 acid by a small fragment of caustic potash. A piece of phosphorus 

 will in a few hours absorb all its oxygen, and an ignited mass of the 

 rare metal titanium will remove its nitrogen. 



A few words will now suffice to apply these facts to the absorption 

 of the nutritive gases by vegetation. 



The cells of plants are permeable to gases, as is especially manifest 

 from what has been stated regarding the separation or evaporation of 

 gaseous water from leaves. They too, or some portions of their con- 

 tents, absorb or condense carbonic acid and ammonia in a similar way, 

 or at least with the same effect as potash absorbs carbonic acid. As 

 fast as these bodies are removed from the atmosphere surrounding or 

 occupying the cells, so fast they are re-supplied by diffusion from 

 without ; so that although the quantities of gaseous plant-food con- 

 tained in the air are, relatively considered, very small, they are by 

 this grand natural law made to flow in continuous streams toward 

 every growing vegetable cell. 



LECTURE III. 



THE SOIL AS RELATED TO AGRICULTURAL PRODUCTION. 



No agricultural plant flourishes naturally except its roots are sit- 

 uated in a soil. The soil is that upon which the farmer spends his 

 labor; the atmosphere, the weather, he cannot control. His art 

 enables him, however, so to modify and adapt the soil that all the 

 deficiencies of the atmosphere or the vicissitudes of climate cannot 

 deprive him of a reward for his exertions. 



The soil has a two-fold function. In the first instance, it forms the 

 appropriate support and home of the plant, is its birthplace, the 

 station where it runs through all the stages of i£s development, and 

 the protection beneath which its roots or seeds survive the desolation 

 of winter to gladden every spring-time with renewed growth. In the 

 second place, it is the exclusive source of an indispensable part of the 

 food of all agricultural plants, and the medium through which another 

 larger share of their nutriment is accumulated and presented to them. 



In nature we observe a vast variety of soils, which often differ as 

 much in their fertility as they do in their appearance. We find large 



