111. 



From this t-t.le it appears that one pound of the average agri- 



cultur-<l soil may have from nbout 400 &&& square feet, in the case of 

 coarse sand, to 2000 square feet internal surface area, in the case of 

 the avenge clay. A more rear->onabl* basis of comparison, oecause of di 

 ferences in volume weight, is th^.t of one cubic foot of Uie material, a 

 as shown t>y the fourth column, Iron, which it appears that these soils 

 have from one to three acres of surface area. These -\re otrikin differ- 

 ences, particularly those "bet-ween soils i 9 ^lich represent extre- 

 mes in li.iit and h il3, respectively. l<ombyr 8 is the sand-hill 

 soil of the Cp.rolirrTi, "-na is of ly lo^v agricultural value. 

 Number 9, !-ioh- :t cl~y, occurs in L rn llorih Dakota, -md is derived 

 from shnls rock. The ran^ in surf rea per cubifi foot of these soife 

 <i frorn 1/12 acre, for the s^i'iiH, to almost 5 ^cres f r - il{ - clay. The 

 latter contains ?6;' of clay in the subsoil, the former 2, 



,e surface area of the particles in a given wei'jht of soil may 

 be c^lcul : t.ed froic the formula: 



where 



.. s Surface are in square centimeters 

 v * Vean difirrieter in centimeters 

 .tTT^ber of particles in the c 

 ii - "5 1AiA fPnrfcin 



: 3.1416 



in the clnn or separate. 

 (Farticleff supposed spiieiical) 



h. Hel?=tion of water to soil. 



Water as a substance is v-::ry remarkable. It i., used as a unit 

 of weight, of , -.fid br;in,j; a poor conductor of he--t ia raucli used 

 che.ric-'lly . Other characteristics will readily occur to the reader, as 

 resistance to compression, thirst qusnching, f ire -extinguishing, etc. 



soil 



There ?.rcj three forms in \vhich water may exist in soils; 



1} Gravitational or free water, which free to move thru the 

 under the influence of gravity. 



2) Capillary or film water, v/hich is helfl against gravity by 



surface tension of the films of >/-: -er surrounuing tht 

 3)" Hygroscopic moisture, taken fron the air; it 

 . tamo sphere on the surface of the soil particles, when 

 allowed to become air-dry. 



soil particles 

 condenses frora 

 the soil is 



.e hygroscopic power of taking water from the air is proportion- 

 al to the surface. 



dy lew; trkes 2\% of its weight from the 

 Clay " 8 * w " !t M 

 Fe hydrate " 



From i-.ilgard- 7/e lenrn that hygroscopic water is of great impor- 

 tance in regard to plants and treca. :3ach, in an experiment, showed that 

 he could raise plant.- in dry soil, by the aid of water from humid air. 

 In California people do the same thing with oranges, spruce, etc., on 

 1 nd that W-K formerly desert land, v;ith no irrigation. They did this 

 by utilizing hygroscopic water, which is not only iiapur t: nu, but is 

 often fully sufficient for the purpose. 



Hygroscopic ^ater Day be said to be related to teiaperature of the 

 soil, as it prevents over-heating of the soil. The amount of moisture in 

 the soil nay" be misleauin^, for a Band with only 8/' water may produce 

 better crops than a heavy clay with \y/l water. This is because the sand 



