Fertilizers and Shade-crops 195 



dioxid 1 corresponding to 3812 pounds per acre foot. 

 This action continued through a period of three weeks, 

 gradually diminishing, however, until at the end of that 

 period very little of the gas was evolved. One hundred 

 tons per acre of red clover treated in the same way gave 

 off after twelve days five tons of carbon dioxid per acre 

 foot. This investigator also tested the solvent action 

 of pure carbon dioxid on various materials. Pure ground 

 bone meal was placed in a flask, and carbon dioxid was 

 allowed to pass through it. At the end of one hour 

 2.11 per cent of the insoluble phosphoric acid had been 

 made soluble. At the end of two hours 5.21 per cent 

 was made soluble. Ground phosphate rock treated in 

 the same way gave the following results: after one hour 

 .16 per cent of the insoluble phosphoric acid had been 

 made soluble; in two hours .28 per cent. Magnesium 

 phosphate similarly treated yielded 16.33 per cent in 

 one hour and 22.35 per cent in two hours of soluble 

 phosphoric acid. 



Carbonic acid is, then, an important agent in dissolving 

 rock particles, and with its aid latent fertility is brought 

 into a condition to be used by plants. 



Organic matter is often almost entirely consumed 

 under arid conditions very quickly after it is incorporated 

 with the soil. The heat of the sun in conjunction with 

 insufficient moisture produces conditions which oxidize the 

 material, or, in other words, burn it much as though 

 it had been consumed by fire; hence the " burning out 

 of soil," an expression common among farmers. This 



1 Carbon dioxid and carbonic acid gas are synonymous; when com- 

 bined with water, carbonic acid is formed. 



