14 MANUAL OF GENEEAL AGEICULTUEE. 



How to plot the curve. Suppose at 8 o'clock it was 

 found that the temperature of the saturated soil was 61 

 degrees F., a dot should be placed half way between 60 

 degrees and 62 degrees on the 8 o'clock line ; if at 9 o'clock 

 the temperature was 61.5 degrees, the second dot should 

 be placed *4 of a division higher on the 9 o'clock line. 

 Continue to put dots for all your temperatures. Connect 

 the dots by a straight or broken line. 



9. PER CENT OF AIR IN SOILS. 



Materials: Three beakers or bottles, graduate, sand, 

 clay, and loam. 



Put 25 cc. of sand in one beaker, 25 cc. of clay in the 

 second, and 25 cc. of loam in the third. Fill the graduate 

 to the 50 cc. mark with water and pour on to each sample 

 until the water just rises to the surface. The amount of 

 water required is an approximate measure of the air space, 

 since the water displaces the air. Figure out the per cent 

 of air space in each sample. 



Question: What effect does size of particles have on 

 total amount of air space ? 



10. SEPARATION OF SAND, SILT AND CLAY IN 



SOILS. 



Materials: Tall beaker of about 500 cc. capacity, 

 flask with long narrow neck, mortar, rubber pestle made 

 by inserting a glass rod into a one-hole stopper. 



Weigh out exactly 20 grams of air-dry soil and place 

 it in a mortar ; add 12 cc. water and rub with the pestle. 

 Let it settle a minute and pour off the muddy water into 

 the tall beaker. Add more water to the mortar and repeat 

 until the water in the mortar no longer gets muddy. The 

 part remaining is coarse sand. 



With small amounts of water wash the sand from the 

 mortar through a funnel into a long necked flask. 



Add water to the beaker containing muddy water 

 until it is nearly filled. Stir and let stand for an hour, or 



