448 Action of the Atmosphere upon newly -deepened Soil. 



diameter, but arranged so that lines passin<T through their centres 

 are mutually perpendicular or parallel, will present a surface of 

 218,166 square feet, and he considers that the substance called 

 platinum black (platinum in a degree of exceedingly fine separa- 

 tion), may possibly offer a surface of this extent. Tlie cells of 

 charred wood are, on an average, ^^^'tioth of an inch in diameter, 

 according to the same high authority, and its surface for a cube 

 inch would therefore by calculation be equal to 100 square feet, 

 supposing the charcoal itself to occupy no space. He however 

 found, by immersing a piece of charcoal in water, that only ■%- of 

 its entire volume are left available for the entrance of gases, which 

 would give a surface of 73 square feet. Now, as Saussure found 

 that charcoal absorbed 35 times its volume of carbonic acid at 

 53°'6 F., and at a pressure of 26'895, these 35 volumes of car- 

 bonic acid are contained in the space which forms ■% of the total 

 volume of the charcoal, and consequently 56 times less than the 

 space originally occupied by the carbonic acid. 



But, according to the experiments of M. Addami, carbonic acid 

 becomes liquid at a pressure of 36*7 atmospheres, the temperature 

 being 53°*6 F. ; we are therefore led to conclude, says Mitscher- 

 lich, that more than one-third of the carbonic acid condensed in 

 the pores of the charcoal is in a liquid state on the walls of the 

 cells. (Mitscherlich, Ann. de Chim. et de Phys., 1843.) Ammo- 

 niacal gas, which liquefies under much less pressure, is absorbed 

 in far greater degree. 



All porous bodies which offer a considerable surface to gases 

 act like charcoal. The humus of the soil and decayed wood 

 approach very nearly to charcoal in this property — decayed oak- 

 wood, according to Liebig, absorbing 72 times its volume of am- 

 moniacal gas after having been completely dried in the air-pump. 

 Platinum black, prepared by Davy's method, surpasses all other 

 known substances in this property, 10 grains, according to Do- 

 bereiner, condense 0"550 cube inch of oxygen, that is to say, one. 

 cube inch would condense 253,440 cube inches. 



The property which some bodies, such as silica, possess of con- 

 densing the humidity of the air, may authorize us, says Mitscher- 

 lich, to conclude that they are adapted for condensing gases ; for 

 in the same manner that solid bodies attract gases, so are they 

 also capable of exercising this attraction upon liquid bodies. 



It will be seen, therefore, how important a matter, even in this 

 respect alone, it is to work the soil when it is in a suitable state 

 for crumbling down and pulverizing under the action of the plough 

 or other implement used, and not to turn it over in a wet clammy 

 condition, when it sticks together or glazes over in continuous 

 solid lumps. The disintegrating effect of the frost upon it will 

 be also appreciated. 



