376 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



dry condition, absorb traces only of carbonic acid, but nota- 

 bly larger quantities in a moist Condition. Exposed to the 

 rays of the sun when moist, they lose the carbonic acid ab- 

 sorbed, but in the shade again take it up gradually. The ab- 

 sorption of carbonic acid by the pure mixture is, neverthe- 

 less, quite inconsiderable compared with that containing hy- 

 drated oxide of iron. 4. The percentage of carbonic acid in 

 hydrated oxide of iron is constantly very considerable, even 

 if variable ; the difference depending upon the density of the 

 deposit, the temperature at which this is dried, and upon its 

 decree of moisture. 5. The amount of carbonic acid in the 

 soils increases in proportion to their percentage of hydrated 

 oxide of iron. 6. The action of the sun's heat upon dry mix- 

 tures of earth is to drive out a large part of all the carbonic 

 acid absorbed. 7. Moist mixtures of earth lose all their car- 

 bonic acid under the action of the sun's rays much easier 

 than dry. 8. The relation of oxygen to the nitrogen is alter- 

 ed by moisture in favor of the latter. 9. By heating to 212 

 Fahrenheit nearly all the carbonic acid is driven out from 

 mixtures of earth. 10. According to all the experiments, 

 mixtures of earth give off carbonic acid under the influence 

 of an elevated diurnal temperature, but the supply is again 

 renewed during the night; the percentage also is greater in 

 the morning than toward evening. 11. Direct experiments 

 upon the action of hydrated oxide of iron and water upon 

 carbonate of lime prove in the most striking manner the sol- 

 vent action under its influence in giving off carbonic acid. 

 19 (7, November 25, 1871, 384. 



ABSOEBENT POWER OF SOILS. 



We hear more or less nowadays of the " absorbing power 

 of the soil ;" this referring to that peculiarity by which the 

 various soluble substances, particularly, however, inorganic, 

 and among them a series of plant nutrients, are so deposited 

 or held that their solution, filtered through the earth, emerges 

 much poorer in these substances, in consequence of this fil- 

 tration, than when entering. . A proof of this property in the 

 soil is shown by a simple experiment, which consists in fill- 

 ing a bottle (having a small hole at the bottom) with fine 

 river sand, or dug and sifted garden earth. If, now, dung- 

 water, quite offensive in smell, be poured into this gradually, 



