66 



No. 9. Not mulched. (Placed in draft). 



No. 10. Not mulched. (Placed in draft). 



Fill the cylinders to the same level Mith distilled water every twenty-four hours 

 for one week and keep a careful record of the amount of water used each day. The 

 "S" glass tube {a, tig. 16) will be used to determine the exact level to which the 

 tubes should be filled. 



The cylinder which evaporated the least water during tlie i)eriod of observation 

 should be the one having the most effective mulch. 



In recording results show the amount of water put in each cylinder daily, and also 

 the total amount for each cylinder for the entin^ run of the experiment. 



- Experiment No. S. 



THE POWER OF AlK-DRY SOIL TO .\BSOKH MOISTl'KE FROM THE AIR. 



Use soils Nos. 1 , 2, 3, and 4 in this experiment. Place 400 grams of air-dry soil from 

 the bin in a shallow zinc tray (fig. 17"), spreading it out as uniformly as possible. 



Fic;. 17.— Dctcriuiuiiig the power of air-dry soils to absorb moisture from tlie air. 



After weighing the tray (lid on) with the soil, place an empty weighed box, together 

 with the others (lids off) , upon a shelf in the pneumatic trough. Place a thermome- 

 ter in the trough and at each weighing read the temperature. Weigh each box (lid 

 on) every twenty-four hours and deduct the increase in weight of the empty box 

 from the increase in weight of each of the other boxes. Repeat the weighings every 

 twenty-four hours until with the same conditions of temperature an approximately 

 constant weight is obtained. The moisture retained is calculated for 100 grams of the 

 soil dried at 110° C. Add to this increased weight per 100 grams of air-dry soil the 

 weight of hygroscopic water contained in 100 grams of the air-dry soil. This will 

 give the total amount of water taken from the air liy 100 grams of water-free soil. 



Determine the hygroscopic moisture of each soil with a special sample at the time 

 of starting the experiment. 



This experiment brings out the fact tiiat dry soils absorb only a very small amount 

 of moisture from the air, even when the air is saturated, thus correcting an opinion- 

 which is prevalent but erroneous. 



