MANUAL OF GENEEAL AGEICULTUEE. 17 



Continue the experiment at least six weeks, adding 

 measured quantities of water to the cans as they need it 

 to keep the surfaces in good condition for crop growth. 

 At the end of the required time dig up the cans, wipe the 

 outsides clean and weigh. Add to the original weight of 

 each can of soil, the weight of the water added, and sub- 

 tract from the result the last weight of the can. The dif- 

 ference represents the amount of water evaporated. Tab- 

 ulate the results. 



Questions: How may a farmer obtain an artificial 

 mulch ? A natural mulch ? 



14. EFFECT OF VEGETABLE MATTER ON THE CAP- 



ILLARY RISE OF WATER. 



Materials: Air-dry soil, sawdust, well rotted ma- 

 nure, tubes as indicated in experiment. 



Obtain three glass tubes about an inch in diameter 

 and two feet long. Close the ends of each by means of 

 cheesecloth firmly tied on. Fill one tube with well pulver- 

 ized air-dry soil and compact slightly. Into a second tube 

 place the same kind of soil to the depth of one-half its 

 length, and then place a two-inch layer of sawdust, and 

 finally fill to the top with soil and compact as above. In 

 the third tube use finely divided well-rotted manure in 

 place of sawdust. Place the tubes so that the lower ends 

 stand about an inch deep in water. At the next labora- 

 tory period notice the rise of capillary water. Leave for 

 another laboratory period, at which time write up the ex- 

 periment and put away the apparatus. Assuming that the 

 crop roots go below the straw or manure plowed under, 

 state the effect of plowing under a large amount of straw 

 or poorly rotted manure. 



15. EFFECT OF A MOIST ATMOSPHERE ON DRY 



SOILS. 



Materials: Sand, clay, loam, 3 fruit jars, 3 small 

 receptacles to hold water and small enough to go into the 

 jars, scales. 



Place 100 grams of air-dry sand in an accurately 

 weighed fruit jar. Place in the jar a small receptacle con- 



