180 HOW CROPS FEED. 
circulation of water in it, no continuous upward movement 
can take place without evaporation. The ease and rapid- 
ity of evaporation, while mainly depending on the condi- 
tion of the atmosphere and on the sun’s heat, are to a cer- 
tain degree influenced by the soil itself. We have already 
seen that the soil possesses a power of absorbing watery 
vapor from the atmosphere, a power which is related both 
to the kind of material that forms the soil and to its state 
of division. This absorptive power opposes evaporation. 
Again, different soils manifest widely different capacities 
for imbibing liquid water—capacities mainly connected 
with their porosity. Obviously, too, the quantity of liquid 
in a given volume of soil affects not only the rapidity, 
but also the duration of evaporation. 
The following tables by Schiibler illustrate the peculi- 
arities of different soils in these respects. The first col- 
umn gives the percentages of liguid water absorbed by 
the completely dry soil. In these experiments the soils 
were thoroughly wet with water, the excess allowed to 
drip off, and the increase.of weight determined. In the 
second column are given the percentages of water that 
evaporated during the space of four hours from the satu- 
rated soil spread over a given surface: 
Quvarizisands: 2.6 6. . oes. diGis . ease ee eee 25 88.4 
GV RUINS 2 oa obijare n-a.r sy 08 * synced bosca’s ak oe aaah 27 Aw 
Dame SA... . 0 Fa fad 6:08 = hte < god A ep oa 29 75.9 
SLY WAT. oe reece cee ek bak on ele ee 34 68.0 
Clay soil, (sixty: per cent clay,):d iss. 0... deus eee 40 52.0 
MIB a8 once boo bo eters done wa aa a ee 51 45.7 
Plo ge Ww NG. o.oo wc ss x vis «0's mein oy ts eee ee 52 32.0 
Heavy clay, (eighty per cent clay,)..:.<.......%. 61 34.9 
Pate craycliyss. Hoc. 6 isis ks Bee 70 319 
Fine, earbenate, of m6 ccs «miss buss an 85 28.0 
arden WO Ae 4.655 2 aco ois Vent oes on pe eee 89 24.5 
TAMING. 35 cone set dads a6 coe mesic wo ses ate een 181 25.5 
Fine carbonate of magnesia. ........1..<dssaene 256 10.8 
It is obvious that these two columns express nearly the 
same thing in different ways. The amount of water re- 
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